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Question: 423
For the following two-way table, compute the value of Ï2.
A. 1.45
B. 4.167
C. 5.2
D. 5.55
E. None of the above
|
(B) The expected two-way table is given by the matrix http://img.apstudy.net/ap/statistics/a500/Ans_Eq_239.jpg http://img.apstudy.net/ap/statistics/a500/Ans_Eq_240.jpg
|
Math/201
|
Math
| null |
Question: 424
A toy company published an advertisement in the local newspaper of a major city and in a children's magazine to see which medium generated more advertising viewership. A random sample of families was taken, and each family was asked to indicate where they had seen the product's advertisement. The results are summarized below.
The advertiser decided to use a chi-square test to see whether there was a relationship between the newspaper and the magazine scores. What would be the degrees of freedom for this test?
A. 3
B. 4
C. 7
D. 8
E. None of the above
|
(A) Degrees of freedom = (rows - 1)(columns - 1) = (4 - 1)(2 - 1) = 3.
|
Math/202
|
Math
| null |
Question: 425
A physical education teacher at a middle school wanted to observe whether there was any association between the weight of a male student and how much weight he could lift. The following data were collected, and a chi-square test was performed. The output indicated a test statistic of 1.745 and a p-value of 0.1865.
Based on the table above, which of the following is a correct statement?
A. Since the value of the test statistic is so small, there is a significant relationship between the weight of an individual and the weight he can lift.
B. The correlation coefficient from a linear regression analysis for these data would be less than 0.20.
C. It is not possible to run a chi-square test on these data since the conditions for conducting this test are not met.
D. The p-value of this test is large, which indicates that no significant relationship exists between the weight of an individual and the weight he can lift.
E. The p-value of this test is small, which indicates that a significant relationship exists between the weight of an individual and the weight he can lift.
|
(D) The p-value for the Ï2 statistic is 0.1865, which is more than any reasonable alpha value. We would fail to reject the null hypothesis. There is insufficient evidence to conclude that an association or relationship exists between the weight of the individual and the weight he can lift.
|
Math/203
|
Math
| null |
Question: 426
A small college is expecting that the ratio of students that will pass compared to those that will fail will be 3 to 1. The college has 880 students. Despite these expectations, 639 students passed, while 241 failed. What is the correct chi-square statistic?
A. 0.669
B. 1.52
C. 2.67
D. 3.152
E. 4.237
|
(C) Once the data is placed in table form for clarity, it is clearly possible to see the difference between the actual and expected range and to calculate each step. The first step is determining the expected value. If the ratio of students expected to fail was meant to be 3 to 1, this means that 660 students were expected to pass, while 220 were expected to fail. The first step is to calculate the difference between the actual and the expected results. After squaring that value, it is necessary to divide this value with the expected value. By dividing this value with the expected results and then summing these two values, the chi-square statistic can be determined to be 2.67.
|
Math/204
|
Math
| null |
Question: 431
A recent study of accident records at a large engineering company in Europe reported the following number of injuries in each shift for one year.
Is there sufficient evidence to say that the number of accidents during the three shifts are not the same? Test at the 0.05, 0.01, and 0.001 levels.
A. There is sufficient evidence at all three levels to say that the number of accidents during each shift are not the same.
B. There is sufficient evidence at both 0.05 and 0.01 levels but not at the 0.001 level.
C. There is sufficient evidence at the 0.05 level but not at the 0.01 and 0.001 levels.
D. There is sufficient evidence at the 0.001 level but not at the 0.05 and 0.01 levels.
E. None of the above
|
(A) http://img.apstudy.net/ap/statistics/a500/Ans_Eq_244.jpg http://img.apstudy.net/ap/statistics/a500/Ans_Eq_245.jpg With df = 3, the critical Ï2-values for 0.05, 0.01, and 0.001 are 5.99, 9.21, and 13.82, respectively. Since 3.18 is less than each of those, there is sufficient evidence at all of these levels to say that the number of accidents on each shift is not the same.
|
Math/205
|
Math
| null |
Question: 432
A farm is expecting to have chickens hatched, where there will be an equal number of yellow, white, and mixed-color chickens. Despite these expectations, of the 900 chickens that were hatched, 276 of them were yellow, 294 of them were white, and 330 were mixed color. Which of the following is the correct chi-square statistic?
A. 1.47
B. 2.85
C. 3.92
D. 5.04
E. 6.18
|
(D) As a first step, it is important to identify the expected values. The farm was expecting an equal number of chickens of each type, which means that the expected value was 300 for each category. This is shown in the table below. The final result is gained from the sum of the individual statistics, which is 5.04.
|
Math/206
|
Math
| null |
Question: 433
A teacher at a community college is expecting that 10% of her class will get an A on their exam, 15% will get a B, 35% will get a C, 25% will get a D, while 15% will get an F. All of the students participated in the exam. The actual values were that 22 students got an A, 18 got a B, 25 got a C, 15 got a D, and 20 failed the test and got an F. Which of the following is the correct chi-square statistic?
A. 1.92
B. 5.47
C. 17.25
D. 21.24
E. 23.52
|
(E) The first step is determining the expected values. The total value can be gained by summing all of the students, since all students participated in the exam. The total is 22 + 18 + 25 + 15 + 20, which is equal to 100. The corresponding expected values and the calculations are shown in the table below. http://img.apstudy.net/ap/statistics/a500/f0288-02.jpg Based on calculating all of the steps required, the sum is therefore 23.52.
|
Math/207
|
Math
| null |
Question: 434
A building inspector inspects four major construction sites every day. In a sample of 100 days, the number of times each site passed inspection is shown in this chart.
Test the hypothesis that Sites C and D pass inspection twice as often as Sites A and B; that is, that the frequency of passing inspection has the ratio 1:1:2:2.
A. There is sufficient evidence at both the 10% and 5% significance levels that there is not a good fit with the indicated ratio.
B. There is sufficient evidence at the 10% level, but not at the 5% level, that there is not a good fit with the indicated ratio.
C. There is sufficient evidence at the 5% level, but not at the 10% level, that there is not a good fit with the indicated ratio.
D. There is not sufficient evidence at either the 10% or 5% significance levels that there is not a good fit with the indicated ratio.
E. There is not sufficient information to answer the question.
|
(D) We have H0: good fit with a 1:1:2:2 ratio. Noting that 45 + 33 + 74 + 76 = 228, http://img.apstudy.net/ap/statistics/a500/Ans_Eq_249.jpg and http://img.apstudy.net/ap/statistics/a500/Ans_Eq_250.jpg
|
Math/208
|
Math
| null |
Question: 437
A school class is going on a class trip, and a vote is being taken of where the class wants to go. The school expects that half of the students would want to go to Disney World, while the other half would want to go to visit Washington, DC Despite these expectations, only 42 students wanted to go to Washington, DC, while twice as many wanted to go to Disney World. Which of the following correctly identifies the chi-square statistic?
A. 4.1
B. 7
C. 14
D. 17.4
E. 22
|
(C) If the number of students who want to go to Washington, DC, is 42, this means that 84 want to go to Disney World. This means that the school expected that 126/2 = 63 students would want to go on each trip. The final calculation is shown in the table below. This shows us that the final value of the chi-square statistic is 14.
|
Math/209
|
Math
| null |
Question: 441
A company decides to finance a trip as part of a team-building activity for its employees. All 135 employees could decide on whichever location they would visit, and the company expected that the same number of people would go to each of these locations. Despite this expectation, 43 people went to Paris, 59 to London, and 33 to Athens. Which of the following identifies the correct chi-square statistic between the expected and actual number of people?
A. 3.62
B. 5.18
C. 7.64
D. 9.18
E. 11.31
|
(C) Because the company expected each country to be visited by the same number of its employees, this means that it anticipated 135/3 = 45 employees would go to each city. From this information, it is easy to calculate the chi-square statistic as shown in the table below. http://img.apstudy.net/ap/statistics/a500/f0289-02.jpg When we round the result, it indicates that the correct chi-square statistic is 7.64.
|
Math/210
|
Math
| null |
Question: 447
Using the given contingency table, determine whether there is evidence that the type of vote is dependent on gender at the 5% level.
A. The null hypothesis is rejected, which implies there is evidence that the type of vote is dependent on gender.
B. The null hypothesis is not rejected, which implies there is evidence that the type of vote is dependent on gender.
C. The null hypothesis is rejected, which implies that there is no evidence that the type of vote is dependent on gender.
D. The null hypothesis is not rejected, which implies that there is no evidence that the type of vote is dependent on gender.
E. There is not enough information to determine whether the null hypothesis would be rejected.
|
(D) To determine whether the two variables are related, we will use a chi-squared test of independence and get a test statistic of 2.78, which leads us to fail to reject the null hypothesis that the two variables are independent.
|
Math/211
|
Math
| null |
Question: 449
Given the contingency table below, determine the expected frequency of cell 1, 3.
A. 83.7
B. 85
C. 115
D. 116.7
E. 899
|
(D) Cell 1,3 represents the value in the first row and third column. The expected frequency of this cell is http://img.apstudy.net/ap/statistics/a500/Ans_Eq_252.jpg
|
Math/212
|
Math
| null |
Based on the strength of the intermolecular forces in each substance, estimate from greatest to smallest the vapor pressures of each substance in liquid state at the same temperature.
A. propane > ethanal > ethene > methanol
B. ethene > propane > ethanal > methanol
C. ethanal > methanol > ethene > propane
D. methanol > ethanal > propane > ethene
|
B Vapor pressure is dependent on intermolecular forces. The weaker the IMFs are, the easier it is for molecules to escape from the surface of the liquid. To begin, polar molecules have stronger IMFs than nonpolar molecules. Methanol and ethanal are both polar, but methanol has hydrogen bonding meaning it has stronger IMFs (and thus a lower vapor pressure) than ethanal. Ethene and propane are both nonpolar, but propane is larger meaning it is more polarizable than ethene and thus has stronger IMFs and lower vapor pressure.
|
Chemistry/1
|
Chemistry
| null |
When in liquid state, which two substances are most likely to be miscible with water?
A. propane and ethene
B. methanol and propane
C. ethene and ethanal
D. methanol and ethanal
|
D Water is polar, and using "like dissolves like," we know that only polar solvents will be able to fully mix with it to create a homogenous solution.
|
Chemistry/2
|
Chemistry
| null |
Between propane and ethene, which will likely have the higher boiling point and why?
A. propane, because it has a greater molar mass
B. propane, because it has a more polarizable electron cloud
C. ethene, because of the double bond
D. ethene, because it is smaller in size
|
B Both are nonpolar, but propane has a lot more electrons and thus is more polarizable than ethene.
|
Chemistry/3
|
Chemistry
| null |
The graph below shows the amount of potential energy between two hydrogen atoms as the distance between them changes. At which point in the graph would a molecule of $H_2$ be the most stable?
A. Point A
B. Point B
C. Point C
D. Point D
|
C The molecule would be the most stable when it has the largest attractive potential energy, which is represented by a negative sign. While the magnitude of the potential energy may be larger at (A), it is repulsive at that point because the nuclei are too close together.
|
Chemistry/4
|
Chemistry
| null |
Two alloys are shown in the diagrams below—bronze, and steel. Which of the following correctly describes the malleability of both alloys compared to their primary metals?
A. Bronze's malleability would be comparable to that of copper, but steel's malleability would be significantly lower than that of iron.
B. Bronze's malleability would be significantly higher than that of copper, but steel's malleability would be comparable to that of iron.
C. Both bronze and steel would have malleability values similar to those of their primary metals.
D. Both bronze and steel would have malleability values greater than those of their primary metals.
|
C Alloys of any type generally have malleability that is very similar to the metals from which they are created.
|
Chemistry/5
|
Chemistry
| null |
The following diagram shows the relative atomic sizes of three different elements from the same period. Which of the following statements must be true?
A. The effective nuclear charge would be the greatest in element X.
B. The first ionization energy will be greatest in element X.
C. The electron shielding effect will be greatest in element Z.
D. The electronegativity value will be greatest in element Z.
|
D Moving across a period, atomic size decreases. Therefore, atom Z will be farthest to the right (have the most protons), and thus will have the highest electronegativity value.
|
Chemistry/6
|
Chemistry
| null |
Two half-cells are set up as follows:
Half-Cell A: Strip of Cu(s) in $CuNO_3(aq)$
Half-Cell B: Strip of Zn(s) in $Zn(NO_3)_2(aq)$
When the cells are connected according to the following diagram, the following reaction occurs. Correctly identify the anode and cathode in this reaction as well as where oxidation and reduction are taking place.
A. Cu is the anode where oxidation occurs, and Zn is the cathode where reduction occurs.
B. Cu is the anode where reduction occurs, and Zn is the cathode where oxidation occurs. C. Zn is the anode where oxidation occurs, and Cu is the cathode where reduction occurs.
D. Zn is the anode where reduction occurs, and Cu is the cathode where oxidation occurs.
|
C The oxidation state of copper changes from +1 to 0, meaning it has gained electrons and is being reduced, and reduction occurs at the cathode. Zinc's oxidation state changes from 0 to +2, meaning it has lost electrons and is being oxidized, which occurs at the anode.
|
Chemistry/7
|
Chemistry
| null |
Two half-cells are set up as follows:
Half-Cell A: Strip of Cu(s) in $CuNO_3(aq)$
Half-Cell B: Strip of Zn(s) in $Zn(NO_3)_2(aq)$
When the cells are connected according to the following diagram, the following reaction occurs. How many moles of electrons must be transferred to create 127 g of copper?
A. 1 mole of electrons
B. 2 moles of electrons
C. 3 moles of electrons
D. 4 moles of electrons
|
B 127 g is equal to 2 moles of copper, which is what appears on the balanced equation. To change one mole of copper from +1 to 0, 1 mole of electrons is required. Twice as many moles being created means twice as many electrons are needed.
|
Chemistry/8
|
Chemistry
| null |
Two half-cells are set up as follows:
Half-Cell A: Strip of Cu(s) in $CuNO_3(aq)$
Half-Cell B: Strip of Zn(s) in $Zn(NO_3)_2(aq)$
When the cells are connected according to the following diagram, the following reaction occurs. If the $Cu^+ + e^- → Cu(s)$ half reaction has a standard reduction potential of +0.52 V, what is the standard reduction potential for the $Zn^{2+} + 2e^- → Zn(s)$ half reaction?
A. +0.76 V
B. -0.76 V
C. +0.24 V
D. -0.24 V
|
B $ E_{\text{cell}} = E_{\text{red}} + E_{\text{ox}} $
$ 1.28 \, V = 0.52 \, V + E_{\text{ox}} $
$ E_{\text{ox}} = 0.76 \, V $
$ -E_{\text{ox}} = E_{\text{red}} $
$ E_{\text{red}} = -0.76 \, V $
|
Chemistry/9
|
Chemistry
| null |
Two half-cells are set up as follows:
Half-Cell A: Strip of Cu(s) in $CuNO_3(aq)$
Half-Cell B: Strip of Zn(s) in $Zn(NO_3)_2(aq)$
When the cells are connected according to the following diagram, the following reaction occurs. As the reaction progresses, what will happen to the overall voltage of the cell?
A. It will increase as [$Zn^{2+}$] increases.
B. It will increase as [$Cu^{+}$] increases.
C. It will decrease as [$Zn^{2+}$] increases.
D. The voltage will remain constant.
|
C As the reaction progresses, [Cu+] will decrease and [Zn2+] will increase. With a lower concentration on the reactants side and a higher concentration on the products side, the reaction will shift left, decreasing the overall potential of the reaction.
|
Chemistry/10
|
Chemistry
| null |
Two half-cells are set up as follows:
Half-Cell A: Strip of Cu(s) in $CuNO_3(aq)$
Half-Cell B: Strip of Zn(s) in $Zn(NO_3)_2(aq)$
When the cells are connected according to the following diagram, the following reaction occurs. What will happen in the salt bridge as the reaction progresses?
A. The Na+ ions will flow to the Cu/Cu+ half-cell.
B. The Br- ions will flow to the Cu/Cu+ half-cell.
C. Electrons will transfer from the Cu/Cu+ half-cell to the Zn/Zn2+ half-cell.
D. Electrons will transfer from the Zn/Zn2+ half-cell to the Cu/Cu+ half-cell.
|
A The electron transfer does not happen across the salt bridge, eliminating options (C) and (D). As the reaction progresses and [Cu+] decreases in the copper half-cell, positively charged sodium ions are transferred in to keep the charge balanced within the half-cell.
|
Chemistry/11
|
Chemistry
| null |
A solution of carbonic acid, $H_2CO_3$, is titrated with sodium hydroxide, NaOH. The following graph is produced. In addition to $OH^-$, what species are present in the solution during section III of the graph?
A. $H_2CO_3$, $HCO_3^-$, and $CO_3^{2-}$
B. $H_2CO_3$ and $HCO_3^-$
C. $HCO_3^-$ and $CO_3^{2-}$
D. $H_2CO_3$ and $CO_3^{2-}$
|
C During sections I and II, the following reaction occurs: $H_2CO_3(aq) + OH^-(aq) \leftrightarrow HCO_3^-(aq) + H_2O(l)$. The endpoint of that is reached when all $H_2CO_3$ has reacted, meaning that in sections III and IV the following occurs: $HCO_3^-(aq) + OH^-(aq) \leftrightarrow CO_3^{2-}(aq) + H_2O(l)$.
|
Chemistry/12
|
Chemistry
| null |
A solution of carbonic acid, H2CO3, is titrated with sodium hydroxide, NaOH. The following graph is produced. What is the magnitude of the first dissociation constant?
A. 10e-2
B. 10e-4
C. 10e-6
D. 10e-8
|
C During sections I and II, the following reaction occurs: $H_2CO_3(aq) + OH^-(aq) \leftrightarrow HCO_3^-(aq) + H_2O(l)$. The endpoint of that is reached when all $H_2CO_3$ has reacted, meaning that in sections III and IV the following occurs: $HCO_3^-(aq) + OH^-(aq) \leftrightarrow CO_3^{2-}(aq) + H_2O(l)$.
|
Chemistry/13
|
Chemistry
| null |
A solution of carbonic acid, H2CO3, is titrated with sodium hydroxide, NaOH. The following graph is produced. If the concentration of the sodium hydroxide is increased prior to repeating the titration, what effect, if any, would that have on the graph?
A. The graph would not change at all.
B. The pH values at the equivalence points would increase.
C. The equivalence points would be reached with less volume of NaOH added.
D. The slope of the equivalence points would decrease.
|
C A more concentrated NaOH solution means more moles of NaOH are added per drop, so a lower volume of NaOH would be needed to add enough moles to reach the equivalence point.
|
Chemistry/14
|
Chemistry
| null |
Two solutions of potassium carbonate and sodium chloride are mixed together, and the particulate representation below shows what is present after the reaction has gone to completion. Which of the two original solutions is the limiting reagent and why?
A. The potassium carbonate, because of the polyatomic anion
B. The potassium carbonate, because there is no carbonate left after the reaction
C. The calcium chloride, because there is an excess of calcium ions post-reaction
D. The calcium chloride, because the component ions are smaller than those in potassium carbonate
|
B If extra $Ca^{2+}$ ions are in solution, that means there were not enough $CO3^{2-}$ ions present for the $Ca^{2+}$ ions to fully react.
|
Chemistry/15
|
Chemistry
| null |
The structure of two oxoacids is shown below. Which would be a stronger acid, and why?
A. HOCl, because the H–O bond is weaker than in HOF as chlorine is larger than fluorine
B. HOCl, because the H–O bond is stronger than in HOF as chlorine has a higher electronegativity than fluorine
C. HOF, because the H–O bond is stronger than in HOCl as fluorine has a higher electronegativity than chlorine
D. HOF, because the H–O bond is weaker than in HOCl as fluorine is smaller than chlorine
|
D The weaker the O-H bond is in an oxoacid, the stronger the acid will be because the H+ ions are more likely to dissociate. The O-F bond in HOF is stronger than the O-Cl bond in HOCl because fluorine is smaller (and thus more electronegative) than chlorine. If the O-F bond is stronger, the O-H bond is correspondingly weaker, making HOF the stronger acid.
|
Chemistry/16
|
Chemistry
| null |
The following diagrams show the Lewis structures of four different molecules. Which molecule would travel the farthest in a paper chromatography experiment using a polar solvent?
A. Methanol
B. Pentane
C. Acetone
D. Ether
|
A In a polar solvent, polar molecules will be the most soluble (like dissolves like). Of the four options, methanol and acetone would both have dipoles, but those of methanol would be significantly stronger due to the H-bonding.
|
Chemistry/17
|
Chemistry
| null |
Four different acids are added to beakers of water, and the following diagrams represent the species present in each solution at equilibrium. Which acid has the highest pH?
A. Acid 1
B. Acid 2
C. Acid 3
D. Acid 4
|
C The strength of an acid is dependent on the amount it dissociates in solution. A low dissociation is signified by a low presence of hydrogen ions. The weakest acid is choice (C).
|
Chemistry/18
|
Chemistry
| null |
Lewis diagrams for the nitrate and nitrite ions are shown below. Choose the statement that correctly describes the relationship between the two ions in terms of bond length and bond energy.
A. Nitrite has longer and stronger bonds than nitrate.
B. Nitrite has longer and weaker bonds than nitrate.
C. Nitrite has shorter and stronger bonds than nitrate.
D. Nitrite has shorter and weaker bonds than nitrate.
|
C Nitrate has a bond order of 1.33. Nitite has a bond order of 1.5. A higher bond order means shorter and stronger bonds.
|
Chemistry/19
|
Chemistry
| null |
$NO_2$ gas is placed in a sealed, evacuated container and allowed to decompose via the following equation:
$2NO_2(g) ↔ 2NO(g) + O_2(g)$
The graph below indicates the change in concentration for each species over time. What is happening to the rate of the forward reaction at t = 60 s?
A. It is increasing.
B. It is decreasing.
C. It is remaining constant.
D. It is zero.
|
C At equilibrium, the concentrations of all species in the reaction are remaining constant, which shows up as a flat line on the graph. The rate of both the forward and reverse reactions are constant at equilibrium.
|
Chemistry/20
|
Chemistry
| null |
$NO_2$ gas is placed in a sealed, evacuated container and allowed to decompose via the following equation:
$2NO_2(g) ↔ 2NO(g) + O_2(g)$
The graph below indicates the change in concentration for each species over time. As the reaction progresses, what happens to the value of the equilibrium constant Kp if the temperature remains constant?
A. It stays constant.
B. It increases exponentially.
C. It increases linearly.
D. It decreases exponentially.
|
A The only factor that can affect the value of the equilibrium constant is temperature. If the temperature does not change, neither does the equilibrium constant.
|
Chemistry/21
|
Chemistry
| null |
$NO_2$ gas is placed in a sealed, evacuated container and allowed to decompose via the following equation:
$2NO_2(g) ↔ 2NO(g) + O_2(g)$
The graph below indicates the change in concentration for each species over time. What would happen to the slope of the $NO_2$ line if additional $O_2$ were injected into the container?
A. It would increase, then level off.
B. It would decrease, then level off.
C. It would remain constant.
D. It would increase, then decrease.
|
A If additional $O_2$ were injected into the container, the reaction would shift left, increasing the amount of $NO_2$ present. Eventually, the reaction would reach equilibrium again, meaning the lines would level out.
|
Chemistry/22
|
Chemistry
| null |
$NO_2$ gas is placed in a sealed, evacuated container and allowed to decompose via the following equation:
$2NO_2(g) ↔ 2NO(g) + O_2(g)$
The graph below indicates the change in concentration for each species over time. Using the graph, how could you determine the instantaneous rate of disappearance of $NO_2$ at t = 30 s?
A. By determining the area under the graph at t = 30 s
B. By taking the slope of a line tangent to the $NO_2$curve at t = 30 s
C. By using the values at t = 30 s and plugging them into the Kp expression
D. By measuring the overall gas pressure in the container at t = 30 s.
|
B To determine the change in concentration at a specific time, we would need the slope of the line at that point. As the line is curved, the only way to do that (without calculus) is to draw a line tangent to the curve at that point and measure its slope.
|
Chemistry/23
|
Chemistry
| null |
The reaction shown in the following diagram is accompanied by a large increase in temperature. If all molecules shown are in their gaseous state, which statement accurately describes the reaction?
A. It is an exothermic reaction in which entropy increases.
B. It is an exothermic reaction in which entropy decreases.
C. It is an endothermic reaction in which entropy increases.
D. It is an endothermic reaction in which entropy decreases.
|
A The temperature increase is indicative of energy being released, meaning the reaction is exothermic. The entropy (disorder) of the system is increasing as it moves from three gas molecules to five.
|
Chemistry/24
|
Chemistry
| null |
The contents in the three containers on the left in the diagram above are transferred to the container on the right. The volumes of the original containers are exactly the values indicated. The pressure in the first three containers is 1.0 atm. What is the pressure in the container on the right?
A. 3.0 atm
B. 4.0 atm
C. 1.1 atm
D. 0.50 atm
|
C: There are several ways of solving this problem. One way is to determine the moles present in the original containers, which must be the same as in the final container. In each case, moles = n = PV/RT. Numbering the containers from left to right as 1, 2, 3, and 4 gives: https://img.crackap.com/ap/chemistry/a5/Image00498.jpg
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Chemistry/25
|
Chemistry
| null |
The diagram above shows the structure of molecules of CS2 and COS. The boiling point of COS is 223 K, and the boiling point of CS2 is 319 K. Which of the following is the best explanation of why the boiling point of CS2 is higher?
A. The molar mass of CS2 is greater.
B. COS has weaker covalent bonds than CS2.
C. Only CS2 can form intermolecular dipole-dipole forces.
D. COS has stronger intermolecular forces because it is polar and CS2 is not.
|
A: Stronger intermolecular forces lead to higher boiling points. Even though COS has dipole-dipole forces, which are usually stronger than the London dispersion forces present in CS2, the greater molar mass of CS2 leads to a London dispersion force contribution that is sufficient to compensate for the general trend of dipole-dipole forces being stronger than London dispersion forces. This is why comparisons should only be made between molecules of similar molecular masses.
|
Chemistry/26
|
Chemistry
| null |
Which of the following best explains why the boiling point of 2-propanol is lower than the other two compounds in the diagram and table above?
A. Larger molecules get tangled and cannot escape each other.
B. It has weaker hydrogen bonds.
C. It is the lightest of the three.
D. It is a more symmetrical molecule.
|
C: All three compounds are capable of hydrogen bonding; therefore, this cannot be the cause of difference. In general, all other things being equal, it takes less energy to move a lighter molecule from the liquid state to the gaseous state.w
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Chemistry/27
|
Chemistry
| null |
The Dumas method is a procedure for determining the molar mass of a gas. In this procedure the mass of a gas is divided by the moles of gas determined from the ideal gas equation (n = PV/RT). The molar masses of some compounds, such as acetic acid, illustrated above, show significant deviations from the “correct” values. Why does the presence of dimers as illustrated make it unlikely to obtain an accurate molar mass of acids, such as acetic acid?
A. Acetic acid, like all acids, will lose a hydrogen ion, so the molar mass is that of the acetate ion, which is less than that of acetic acid.
B. Acetic acid is a liquid at room temperature, and its boiling point is too high to get accurate results.
C. Acids are too reactive to give accurate results.
D. The presence of strong intermolecular forces (hydrogen bonding) makes the gas nonideal; therefore the ideal gas law is not applicable.
|
D: Strong hydrogen bonds hold two molecules of acetic acid together. Ideal gases have no intermolecular forces. Therefore, the ideal gas law used in experiment is invalid.
|
Chemistry/27
|
Chemistry
| null |
Which of the labeled arrows in the diagram above represents the strongest intermolecular force?
A. A
B. B
C. C
D. D
|
B-This is a dipole-dipole force, which is stronger than a dipole-induced dipole (A and C) or a London dispersion force (D).
|
Chemistry/28
|
Chemistry
| null |
pH versus volume of titrant added
The diagram above represents the idealized titration curve for the reaction of pure sodium carbonate, Na2CO3, with a strong acid such as hydrochloric acid, HCl. E and F represent the pH at the endpoints corresponding to the formation of HCO3- and H2CO3, respectively. G and H correspond to the quantity of acid required to reach the endpoints.
A trial run used a sample of pure sodium carbonate. How does the volume of acid necessary to reach G from 0 compare to the volume of acid necessary to get from G to H?
A. They are the same.
B. It takes more to reach point G.
C. It takes more to get from G to H.
D. It is impossible to determine
|
A: At point G, all the $CO3^{2-}$ has been converted to $HCO^{3-}$ and the moles of $ HCO^{3-}$ will equal the moles of $CO3^{2-}$ originally present plus the quantity of $HCO^{3-}$ originally present. It will require a greater volume of acid to titrate a greater number of moles of $HCO^{3-}$ as required for the $CO3^{2-}$.
|
Chemistry/29
|
Chemistry
| null |
pH versus volume of titrant added
The diagram above represents the idealized titration curve for the reaction of pure sodium carbonate, Na2CO3, with a strong acid such as hydrochloric acid, HCl. E and F represent the pH at the endpoints corresponding to the formation of HCO3- and H2CO3, respectively. G and H correspond to the quantity of acid required to reach the endpoints.
The analysis of a sample contaminated with NaHCO3 gave slightly different results. How does the volume of acid necessary to reach G from 0 compare to the volume of acid necessary to get from G to H for the second sample?
A. It takes more to get from G to H.
B. It takes more to reach point G.
C. They are the same.
D. It is impossible to determine.
|
C: It would be necessary to titrate the strong base and the $CO3^{2-}$ to reach G. However, it is only necessary to titrate the $HCO_{3-}$ to reach H, which means less acid is necessary.
|
Chemistry/30
|
Chemistry
| null |
pH versus volume of titrant added
The diagram above represents the idealized titration curve for the reaction of pure sodium carbonate, Na2CO3, with a strong acid such as hydrochloric acid, HCl. E and F represent the pH at the endpoints corresponding to the formation of HCO3- and H2CO3, respectively. G and H correspond to the quantity of acid required to reach the endpoints.
How could a student determine if there was a strong acid or a strong base contaminant in the original sample?
A. The presence of an acid contaminant would require less acid to reach H from G than to reach G from 0.
B. The presence of a base contaminant would require less acid to reach G from 0 than to reach F from G.
C. The presence of a base contaminant would require more acid to reach G from 0 than to reach F from G.
D. It is impossible to determine.
|
C-It would be necessary to titrate the strong base and the $CO3^{2-}$ to reach G. However, it is only necessary to titrate the $HCO3^{-}$ to reach H, which means less acid is necessary.
|
Chemistry/31
|
Chemistry
| null |
pH versus volume of titrant added
The diagram above represents the idealized titration curve for the reaction of pure sodium carbonate, Na2CO3, with a strong acid such as hydrochloric acid, HCl. E and F represent the pH at the endpoints corresponding to the formation of HCO3- and H2CO3, respectively. G and H correspond to the quantity of acid required to reach the endpoints.
In addition to water, what are the predominant species in solution at F?
A. $\ch{Na2CO3}$ and $\ch{HCl}$
B. $\ch{Na+}$, $\ch{Cl-}$, and $\ch{H2CO3}$
C. $\ch{HCO3-}$ and $\ch{H+}$
D.$ \ch{Na+}$, $\ch{Cl-}$, $\ch{H+}$, and $\ch{CO3^{2-}}$
|
B: At G the $\ch{CO3^{2-}}$ is now $\ch{HCO3-},$ so no $\ch{CO3^{2-}}$ remains. The $\ch{Na+}$ did not react, so it is still present as ions. The $\ch{Cl-}$ is from the HCl and remains as separate ions in solution. After G, the $\ch{H+}$ from the acid begins to convert $\ch{HCO3-}$ to form $\ch{H2CO3}$, which is complete at point F leaving no $\ch{HCO3-}$ in the solution. Other than water, all species are strong electrolytes and exist as ions in solution. The $\ch{H2CO3}$ will be decomposing to $\ch{H2O}$ and $\ch{CO2(g)}$.
|
Chemistry/32
|
Chemistry
| null |
pH versus volume of titrant added
The diagram above represents the idealized titration curve for the reaction of pure sodium carbonate, Na2CO3, with a strong acid such as hydrochloric acid, HCl. E and F represent the pH at the endpoints corresponding to the formation of HCO3- and H2CO3, respectively. G and H correspond to the quantity of acid required to reach the endpoints.
In addition to water, what are the predominant species in solution at F?
At what point on the graph for the titration of pure sodium carbonate is the pH =\ch{ pK_{a2}} for carbonic acid?
A. At point G
B. Halfway between the start and point G
C. At point H
D. Halfway between points G and H
|
D: The pH will equal the pKa2 when the concentration of $HCO_{3-}$ equals the concentration of H2CO3. This occurs when one-half of the $HCO_{3-}$ has been converted to H2CO3.
|
Chemistry/33
|
Chemistry
| null |
What is the reason that the lightest member of Group 15 does not follow the trend of the other members, which show that the boiling point decreases with decreasing atomic mass of the Group 15 element?
The graph shows the variation of boiling point with Group number for the hydrogen compounds of the four lightest members of Group 15 on the periodic table (NH3, PH3, AsH3 and SbH3).
A. Ionic bonds
B. Hybrid orbitals
C. Resonance structures
D. Hydrogen bonding
|
D: Hydrogen bonding may occur when hydrogen is attached directly to N, O, or F.
|
Chemistry/34
|
Chemistry
| null |
A dimer consists of two closely associated molecules. In the gas phase, acetic acid tends to form dimers as illustrated on the left in the above diagram. Acetyl chloride, on the right in the above diagram, is not very efficient in forming dimers. Why is acetic acid better able to form dimers than acetyl chloride?
A. The molecular mass of acetyl chloride is higher than that of acetic acid making it harder for the acetyl chloride to form dimers.
B. It is easier to form a covalent bond between acetic acid molecules than between acetyl chloride molecules.
C. Acetic acid can form strong hydrogen bonds but acetyl chloride can only form weaker dipole-dipole attractions.
D. Acetic acid is an acidic compound but acetyl chloride is a neutral compound.
|
C: The two molecules are hydrogen bonded together. Hydrogen bonding is a relatively strong intermolecular force. Acetyl chloride cannot exhibit anything stronger than dipole-dipole forces, which are, in general, weaker than hydrogen bonds.
|
Chemistry/35
|
Chemistry
| null |
Two compounds with the formula C2H2Cl2 appear in the above diagram. These two compounds are isomers. The molecules are planar and have the approximate structures shown in the diagram. The boiling point of trans-1, 2-dichloroethene is 47.5°C and the boiling point of cis-1,2-dichloroethene is 60.3°C. Which of the following best explains why cis-1,2-dichloroethene has a higher boiling point than its isomer, trans-1, 2-dichloroethene?
A. The higher boiling isomer is more polar than the other isomer.
B. The higher boiling isomer is better able to form hydrogen bonds than the other isomer.
C. The higher boiling isomer has a greater molar mass.
D. The higher boiling isomer has greater London dispersion forces than the other isomer.
|
A: The higher boiling isomer is more polar than the other isomer because the two very electronegative chlorine atoms are on one side, which leads to their polar bonds working together. When the chlorine atoms are on opposite sides, their polar bonds work against each other.
|
Chemistry/36
|
Chemistry
| null |
Use the following information on the bases in the following diagram to answer questions.
https://img.crackap.com/ap/chemistry/a5/Image00543.jpg
Ammonia is only present as a reference. Questions only refer to the other three bases.
https://img.crackap.com/ap/chemistry/a5/Image00544.jpg
All the bases in the diagram behave as Brønsted-Lowry bases in the same way; in each case, they accept a hydrogen ion to the same atom. How is this acceptance of a hydrogen ion accomplished?
A. A hydrogen ion attaches to the lone pair on the nitrogen atom.
B. The hydroxide ion reacts with the hydrogen ion to form water.
C. The hydrogen ion forms a hydrogen bond to the base.
D. The hydrogen ion combines with a hydrogen atom from the base to form H2 gas
|
A: As in ammonia, all these compounds behave as Brønsted-Lowry bases by accepting a hydrogen ion. The reaction involves the hydrogen ion attaching to the lone pair on the nitrogen atoms.
|
Chemistry/37
|
Chemistry
| null |
Use the following information on the bases in the following diagram to answer questions.
https://img.crackap.com/ap/chemistry/a5/Image00543.jpg
Ammonia is only present as a reference. Questions only refer to the other three bases.
https://img.crackap.com/ap/chemistry/a5/Image00544.jpg
Which of the following explains why the pH of a hydroxylamine solution is lower than any of the other solutions?
A. The $-OH$ is capable of donating a hydrogen ion, which will lower the pH.
B. The presence of carbon makes the bases less stable.
C. The presence of the very electronegative oxygen inhibits the nitrogen atom from donating its electron pair.
D. There is insufficient information to explain this observation.
|
C: These are all bases because the nitrogen atom is capable of reacting with a hydrogen ion by donating its lone pair to the hydrogen ion. The oxygen atom pulls electron density away from the nitrogen atom causing the nitrogen atom to attract the lone pair more strongly making it less able to donate the pair to a hydrogen ion.
|
Chemistry/37
|
Chemistry
| null |
Which of the compounds in the above diagram is capable of participating in hydrogen bonding?
A. $C_3H_9N$
B. $CH_3F$
C. $C_2H_6O$
D. $C_4H_11$
|
D: Hydrogen bonding is possible when hydrogen is attached to N, O, and F. D is the only compound in the diagram where this is true. The simple presence of hydrogen and N, O, or F is insufficient.
|
Chemistry/37
|
Chemistry
| null |
Ammonia is the best-known nitrogen-hydrogen compound; however, there are a number of other nitrogen-hydrogen compounds, three of which are in the above diagram. Which of these has the longest average N-N bond length?
A. $N_2H_2$
B. $N_3H_3$
C. $N_4H_4$
D. They are all the same.
|
C: The higher the average number of bonds between the nitrogen atoms, the shorter the bond is. For diazene there are two bonds, for triazene the average is 1.5 bonds, and for tetrazene the average is 1.33 bonds. The length of the average bond length increases in the order 2 < 1.5 < 1.33.
|
Chemistry/38
|
Chemistry
| null |
Use the information on the acids in the following diagram to answer questions.
Sample solutions of each of the three acids were titrated with 0.10 M sodium hydroxide, NaOH. Each of the acid solutions had a concentration of 0.10 M. Which of the acid titrations had the highest pH at the endpoint?
A. Formic acid
B. Benzoic acid
C. Chloroacetic acid
D. They all had a pH of 7 at the endpoint.
|
B: The weakest acid (smallest Ka) will have the highest pH at the endpoint.
|
Chemistry/39
|
Chemistry
| null |
Use the information on the acids in the following diagram to answer questions.
A student prepares three buffer solutions. Each solution is 1.0 M in one of the acids in the table and 1.0 M in its corresponding sodium salt. Which of the solutions has the greatest buffer capacity with respect to added NaOH and why?
A. The benzoic acid buffer because it is the strongest acid.
B. The chloroacetic acid buffer because it is the strongest acid.
C. The formic acid buffer because it donate both of its hydrogen atoms.
D. All are the same.
|
D: The buffer capacity only depends on the number of moles present. All three solutions have the same number of moles.
|
Chemistry/40
|
Chemistry
| null |
Cyclopropane, pictured above, is a relatively unstable compound. As seen in the diagram, the carbon atoms form the corners of an equilateral triangle and each carbon atom has two hydrogen atoms attached to complete an octet of electrons around the carbon atoms. Based upon this structure, why is cyclopropane a relatively unstable compound?
A. Hydrocarbon compounds are relatively unstable in general.
B. Compounds that have identical atoms bonded to each other are relatively unstable.
C. The bonds do not match the angles.
D. There is no resonance to stabilize the compound.
|
C: A carbon atom with four single bonds should be tetrahedral. Tetrahedral atoms have an ideal bond angle of 109.5°C. However, the carbon atoms in cyclopropane are at the corners of an equilateral triangle, where the ideal angle is 60°C. The discrepancy between the two ideal bond angles leads to the relative instability of cyclopropane.
|
Chemistry/41
|
Chemistry
| null |
Refer to the following information.
$N_2O_4(g)\rightleftarrows 2NO_2(g)$
$N_2O_4(g)$ decomposes into $NO_2(g)$ according to the equation above. A pure sample of $N_2O_4(g)$ is placed into a rigid, evacuated, 0.500 L container. The initial pressure of the $N_2O_4(g)$ is 760 atm. The temperature is held constant until the $N_2O_4(g)$ reaches equilibrium with its decomposition products. The figure below shows how the pressure of the system changes while reaching equilibrium. Why does the pressure rise in this experiment?
A. The intermolecular attractions inside the container decrease, so the molecules strike the walls more frequently.
B. The intermolecular attractions inside the container increase, which increases the force as molecules collide with the walls of the container.
C. The average kinetic energy increases as the reaction continues.
D. The number of particles striking the container walls per unit time increases.
|
D: As $N_2O_4(g)$ reacts, we get twice as many molecules, thus increasing the pressure.
|
Chemistry/42
|
Chemistry
| null |
Refer to the following information.
$N_2O_4(g)\rightleftarrows 2NO_2(g)$
$N_2O_4(g)$ decomposes into $NO_2(g)$ according to the equation above. A pure sample of $N_2O_4(g)$ is placed into a rigid, evacuated, 0.500 L container. The initial pressure of the $N_2O_4(g)$ is 760 atm. The temperature is held constant until the $N_2O_4(g)$ reaches equilibrium with its decomposition products. The figure below shows how the pressure of the system changes while reaching equilibrium. The figure above gives us information about all the following except
A. the activation energy
B. the reaction rate
C. the position of equilibrium
D. the order of reaction
|
A: The only way we know of to determine the activation energy is to measure reaction rates at different temperatures. However, no temperatures are mentioned.
|
Chemistry/43
|
Chemistry
| null |
Refer to the following information.
$N_2O_4(g)\rightleftarrows 2NO_2(g)$
$N_2O_4(g)$ decomposes into $NO_2(g)$ according to the equation above. A pure sample of $N_2O_4(g)$ is placed into a rigid, evacuated, 0.500 L container. The initial pressure of the $N_2O_4(g)$ is 760 atm. The temperature is held constant until the $N_2O_4(g)$ reaches equilibrium with its decomposition products. The figure below shows how the pressure of the system changes while reaching equilibrium. By how much will the equilibrium pressure increase if this reaction goes to completion?
A. 760 torr
B. 900 torr
C. 634 torr
D. 886 torr
|
C: The pressure will increase to 1520 torr, which is 634 torr greater than 886 torr.
|
Chemistry/44
|
Chemistry
| null |
Refer to the following information.
$N_2O_4(g)\rightleftarrows 2NO_2(g)$
$N_2O_4(g)$ decomposes into $NO_2(g)$ according to the equation above. A pure sample of $N_2O_4(g)$ is placed into a rigid, evacuated, 0.500 L container. The initial pressure of the $N_2O_4(g)$ is 760 atm. The temperature is held constant until the $N_2O_4(g)$ reaches equilibrium with its decomposition products. The figure below shows how the pressure of the system changes while reaching equilibrium. What can be said about the equilibrium constant, Kp, for this reaction?
A. $K_p$ > 1
B. $K_p$< 1
C. $K_p$= 1
D. The data do not allow us to estimate the value of $K_p$.
|
B: If the pressure rises to 886 torr, which means that 126 × 2 torr of $NO_2$ is produced and 634 torr of $N_2O_4$ remain. Dividing both by 760 torr gives 0.332 atm $NO_2$ and 0.834 atm $N_2O_4$. Since $K_P = (0.332)^2/(0.834)$, we can see that the result must be less than 1.
|
Chemistry/45
|
Chemistry
| null |
Refer to the following information.
This formation equation for the reaction synthesizing RbBr(s) can be separated into a series of steps. Which of the steps in the table above are endothermic?
A. ΔH°(1) and ΔH°(2) only
B. ΔH°(1), ΔH°(2), and ΔH°(3) only
C. ΔH°(3) only
D. ΔH°(3) and ΔH°(4) only
|
B: All processes that separate molecules or break bonds are endothermic.
|
Chemistry/46
|
Chemistry
| null |
Refer to the following information.
This formation equation for the reaction synthesizing RbBr(s) can be separated into a series of steps. If this reaction goes to completion, producing RbBr from the reactants, and if you use the overall chemical equation to estimate the entropy change for this process, which of the following statements is correct?
A. The reaction is favorable and driven by the enthalpy change since the entropy decreases in this process.
B. The reaction is unfavorable since the entropy change is a large negative value.
C. The reaction is favorable and driven by both enthalpy and entropy changes.
D. The reaction is unfavorable because of the enthalpy and entropy changes.
|
A: Using general rules, we have a solid and a liquid combining to make one formula unit of solid. A small change in entropy is expected. The enthalpy is very large compared with the entropy values, especially for binary compounds. So this answer is reasonable.
|
Chemistry/47
|
Chemistry
| null |
n-pentane ($C_5H_{12}$ or $CH_3CH_2CH_2CH_2CH_3$) and 2,2-dimethylpropane ($C_5H_{12}$ or $(CH_3)_4C$), shown above as space-filling models, each have the same number of carbon and hydrogen atoms but the atoms are arranged differently. n-pentane boils at 36.1 °C, and 2,2-dimethylpropane boils at 9.5 °C. Which statement best explains these data?
A. The long chains of n-pentane make it more difficult for them to reach the liquid surface and vaporize.
B. The long chains of n-pentane provide more sites for London attractive forces for neighboring molecules to have an effect on each other.
C. The compact structure of the 2,2-dimethylpropane directs the attractive forces internally in the molecule.
D. The bonds in the n-pentane are weaker, allowing small parts of the molecule to vaporize easily.
|
B: Although London forces tend to be small, molecules that allow many sites for interaction experience stronger attractions
|
Chemistry/48
|
Chemistry
| null |
Refer to the following information.
Four different acid solutions of 0.0100 M are prepared, and their pH values are recorded on a laptop computer. One of the solutions contains more than just an acid. At the point designated as "add," all four solutions are diluted with an equal volume of water. The bottom line represents solution 1, and the top line represents solution 4. Which of the four acids is best described as a strong acid?
A. Solution 1
B. Solution 2
C. Solution 3
D. Solution 4
|
A: A 0.010 M solution of a strong acid should have a pH = 2.00.
|
Chemistry/49
|
Chemistry
| null |
Refer to the following information.
Four different acid solutions of 0.0100 M are prepared, and their pH values are recorded on a laptop computer. One of the solutions contains more than just an acid. At the point designated as "add," all four solutions are diluted with an equal volume of water. The bottom line represents solution 1, and the top line represents solution 4. Which acid(s) will require the most 0.0050 M NaOH to neutralize 25.0 mL of a 0.010 M solution of the acid?
A. Solution 1
B. Solution 2
C. Solution 3
D. They will all require the same volume of NaOH.
|
D: All of the acid solutions, 1, 2, and 3, will require the same amount of base to reach the end point.
|
Chemistry/50
|
Chemistry
| null |
Refer to the following information.
Four different acid solutions are prepared, and their pH values are determined and tabulated below. Using the data in the table above, which is the weakest acid?
A. Acid 1
B. Acid 2
C. Acid 3
D. Acid 4
|
D: The weakest acid has the lowest $[H^+]$ and the highest pH.
|
Chemistry/51
|
Chemistry
| null |
Refer to the following information.
Four different acid solutions are prepared, and their pH values are determined and tabulated below. Which of the four acids is best described as a strong acid?
A. Acid 1
B. Acid 2
C. Acid 3
D. Acid 4
|
B: A strong acid is completely ionized and the molar concentration is equal to the $[H^+]$.
|
Chemistry/52
|
Chemistry
| null |
Refer to the following information.
Four different acid solutions are prepared, and their pH values are determined and tabulated below. Which of the following operations will produce an effective buffer solution?
A. 50.0 mL of 0.010 M acid 3 mixed with 50.0 mL of 0.010 M acid 2
B. 50.0 mL of 0.010 M acid 2 mixed with 25.0 mL of 0.010 M NaOH
C. 50.0 mL of 0.0050 M acid 4 mixed with 0.25 mL of 0.0050 M NaOH
D. 50.0 mL of 0.0010 M acid 2 mixed with 55.0 mL of 0.0010 M NaOH
|
B: This is the only way to have a significant concentration of both the conjugate acid and conjugate base.
|
Chemistry/53
|
Chemistry
| null |
Refer to the following information.
Four different acid solutions are prepared, and their pH values are determined and tabulated below. Each of the acids were titrated with NaOH to the end point. The end point pH values are shown on the last line of the table. The end point pH values
A. suggest that acid 3 is strong and all the rest are weak
B. suggest that all the acids are weak
C. suggest that acid 1 is most likely polyprotic
D. suggest serious problems with the pH meter
|
C: An end point lower than pH 7 is indicative of a polyprotic acid.
|
Chemistry/54
|
Chemistry
| null |
The graph above shows the distribution of kinetic energies of a system containing a large number of SO2 molecules at 300 K. Which letter shows the average kinetic energy of this system?
A. A
B. B
C. C
D. D
|
C: The average kinetic energy is a little above the maximum for this type of distribution curve.
|
Chemistry/55
|
Chemistry
| null |
Three 1-liter flasks are connected to a 3-liter flask by valves. The 3-liter flask is evacuated to start and the entire system is at 585 K. The first flask contains oxygen, the second hydrogen, and the third nitrogen. The pressure of hydrogen is 1.65 atm. The amounts of gas molecules are proportional to their representations in the flasks. If valve 2 is opened first and then the rest of the valves are opened, what will the pressure be after the first valve is opened and after they all are opened? Assume the connections have negligible volume.
Valve 2 Opened All Valves Opened
A. 1.0 atm 0.5 atm
B. 0.41 atm 0.82 atm
C. 0.81 atm 1.65 atm
D. 2.0 atm 1.0 atm
|
B: Opening valve 2 will increase the volume by 4 times, so the pressure will be 1/4 of the starting pressure. The amount of particles is doubled by opening the second two valves, so the pressure doubles.
|
Chemistry/56
|
Chemistry
| null |
A mass spectrum of a naturally occurring sample of an element is shown above. What is the element?
A. Ca
B. Ne
C. K
D. Not enough information is provided.
|
B: This element is 90 percent of an isotope with a mass of almost 20 and 10 percent of an isotope with a mass close to 22. We calculate 0.90 × 20 + 0.10 × 22 = 20.2, which is closest to the average mass of Ne.
|
Chemistry/57
|
Chemistry
| null |
Refer to the titration curve below, which is of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.125 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the above graph. Which of the following describes the base that is being titrated?
A. The base is dibasic since two end points are observed.
B. The concentration of the base is exactly 0.125 M.
C. The concentration of the base is slightly more than 0.125 M.
D. The concentration of the base is slightly less than 0.125 M.
|
D: The end point is at about 22.5 mL, so (25.0 mL)($M_b$) = (22.5 mL)(0.125 M). Inspection of this equation reveals that the concentration is less than 0.125 M.
|
Chemistry/58
|
Chemistry
| null |
Refer to the titration curve below, which is of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.125 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the above graph. Between which two points on the titration curve can the solution be described as a buffer?
A. None, it is impossible for a titration solution to also be a buffer solution.
B. A to F
C. A to D
D. D to F
|
C: Between these two points, there is a significant amount of both the conjugate acid and the conjugate base.
|
Chemistry/59
|
Chemistry
| null |
Refer to the titration curve below, which is of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.125 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the above graph. For the best results with a visual indicator (one that changes color), what will optimize the results?
A. Add the indicator two drops before the end point.
B. Choose an indicator that has a pK that is close to the end point pH.
C. Choose an indicator that has complementary colors.
D. Choose a polyprotic indicator.
|
B: Choosing an indicator with the same $pK_a$ as the end point pH assures the sharpest color change and closest agreement of the end point (experimental) with the equivalence point (theoretical or calculated point).
|
Chemistry/60
|
Chemistry
| null |
Refer to the titration curve below, which is of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.125 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the above graph. If the student uses a pH indicator that changes color from pH 6 to 8, which statement best characterizes the expected observations?
A. The observed color change will be distinct, and the calculated molarity of the base will be accurate.
B. The color will change slowly, and the end point volume will be low.
C. The color will change slowly, and the calculated molarity of the base will be low.
D. The observed color change will be distinct, but the calculated molarity of the base will be high.
|
B: Most of the indicator color change is outside the inflection part of the curve.
|
Chemistry/61
|
Chemistry
| null |
Refer to the titration curve below, which is of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.125 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the above graph. Which arrow points to the place on the curve where pH = pKaof the conjugate acid of the base?
A. A
B. E
C. C
D. F
|
C: The $pH = pK_a$ when the concentration of the conjugate acid and of the conjugate base are equal. This occurs at point C on the curve. The conjugate acid of the base we are titrating in this case is $HB^+$ in the weak base equilibrium $B + H_2O → HB^+ + OH^-$.
|
Chemistry/62
|
Chemistry
| null |
In the diagram above, which labeled arrow is pointing toward a covalent bond and which is pointing toward a hydrogen bond?
Covalent Bond Hydrogen Bond
A. 1 2
B. 2 1
C. 3 4
D. 4 3
|
D: Covalent bonds are shown as solid lines and hydrogen bonds are shown as dashed lines when aligned with the correct atoms.
|
Chemistry/63
|
Chemistry
| null |
Morphine, $C_{17}H_{19}NO_3$ (shown above), has a $K_b = 8.0 × 10^{-7}$. If a 0.00100 M solution of morphine is prepared, the expected pH will be in which one of the following pH ranges?
A. 2 to 4
B. 4 to 6
C. 8 to 10
D. 10 to 12
|
C: The $[OH^-]$ will be the square root of the $K_b$ × concentration. We can calculate $(8.0 × 10^{-7})(0.0010) = 8.0 × 10^{-10}$, and the square root is approximately $3 × 10^{-5}$. Our answer is between $10^{-5}$ and $10^{-4}, so the pOH is between 4 and 5. The pH will be between 9 and 10.
|
Chemistry/64
|
Chemistry
| null |
The volume of a gas is charted over time, giving the above results. Which of the following options provides a possibel explinatin of what was happening to the gas during each phase of the graph?
A. During phase I, the temperature decreased while the pressure increased. During phase II, the temperature was held constant as the pressure decreased.
B. During phase I, the temperature increased while the pressure was held constant. During phase II, the temperature and pressure both decreased.
C. During phase I, the temperature was held constant while the pressure increased. During phase II, the temperature and pressure both decreased.
D. During phase I, the temperature and pressure both increased. During phase II, the temperature was held constant while the pressure decreased.
|
B In phase I, an increased temperature means the molecules are moving faster and will spread out more, leading to an increased volume. For the volume to remain constant in phase II, either both pressure and volume have to remain constant, or they both have to increase or decrease together, as they are inversely proportional.
|
Chemistry/65
|
Chemistry
| null |
The above experiment was performed several times, and the data was gathered as shown in the figure. What is the rate law for this reaction?
A. rate = k[NO][Br$_2$]$^2$
B. rate = k[NO]$^2$[Br$_2$]$^2$
C. rate = k[NO][Br$_2$]
D. rate = k[NO]$^2$[Br$_2$]
|
D Between trial 1 and 3, the concentration of NO doubled while the concentration of Br$_2$ held constant, and the rate went up by a factor of four. So, the reaction is second order with respect to NO. Between trial 1 and 2, the concentration of NO was held constant while the concentration of Br2 doubled, and the rate went up by a factor of two. Thus, the reaction is first order with respect to Br$_2$.
|
Chemistry/66
|
Chemistry
| null |
Regarding reaction II, to achieve the products present in the above diagram how many moles of each reactant must be present prior to the reaction?
A. 1.0 mol of CH$_4$ and 2.0 mol of H$_2$O
B. 2.0 mol of CH$_4$ and 2.0 mol of H$_2$O
C. 2.0 mol of CH$_4$ and 3.0 mol of H$_2$O
D. 3.0 mol of CH$_4$ and 2.0 mol of H$_2$O
|
C 2.0 moles of CH$_4$ would react with 2.0 moles of H$_2$O, leaving 1.0 mole left. It would also create 6.0 moles of H$_2$ and 2.0 moles of CO.
|
Chemistry/67
|
Chemistry
| null |
Identify the three gases represented on the Maxwell-Boltzmann diagram above. Assume all gases are at the same temperature.
A. I \( \mathrm{H_2} \) II \( \mathrm{N_2} \) III \( \mathrm{F_2} \)
B. I \( \mathrm{H_2} \) II \( \mathrm{F_2} \) III \( \mathrm{N_2} \)
C. I \( \mathrm{F_2} \) II \( \mathrm{N_2} \) III \( \mathrm{H_2} \)
D. I \( \mathrm{N_2} \) II \( \mathrm{F_2} \) III \( \mathrm{H_2} \)
|
C At identical temperatures, the gases would all have identical amounts of kinetic energy. In order for that to happen, the gas with the lowest mass (H$_2$) would have to have the highest average velocity, and the gas with the highest mass (F$_2$) would have to have the lowest average velocity
|
Chemistry/68
|
Chemistry
| null |
The above diagrams shows the decomposition of hydrogen peroxide in a sealed container in the presence of a catalyst. What is the overall order for the reaction?
A. Zero order
B. First order
C. Second order
D. Third order
|
B In 200 seconds, half of the original sample decayed. In another 200 seconds, half of the remaining sample decayed. This demonstrates a first order reaction
|
Chemistry/69
|
Chemistry
| null |
One of the resonance structures for the nitrite ion is shown above. What is the formal charge on each atom?
A. O$_x$ -1; N +2; O$_y$ -1
B. O$_x$ +1; N -1; O$_y$ 0
C. O$_x$ 0; N 0 ; O$_y$ -1
D.O$_x$ -1; N 0 ; O$_y$ 0
|
D O$_x$ has 6 valence electrons and 7 assigned electrons: 6 - 7 = -1. Both O$_y$ and the N atoms have the same number of valence and assigned electrons, making their formal charges zero.
|
Chemistry/70
|
Chemistry
| null |
The following diagram supports which of the following conclusions about the reaction shown below?
A. There is an increase in entropy.
B. Mass is conserved in all chemical reactions.
C. The pressure increases after the reaction goes to completion.
D. The enthalpy value is positive.
|
B The amount of matter is equal on both sides of the reaction. None of the other options are supported by the diagram. --------------------- Source Url:https:// /ap/chemistry/question-118-answer-and-explanation.html
|
Chemistry/71
|
Chemistry
| null |
The concentrations of the reactants and products in the reaction represented by the above graph are found to be changing very slowly. Which of the following statements best describes the reaction given that the reaction is exergonic? (ΔG < 0)
A. The reaction is under kinetic control.
B. The reaction has reached a state of equilibrium.
C. The reaction is highly exothermic in nature.
D. The addition of heat will increase the rate of reaction significantly.
|
A Reactions with high activation energies that do not proceed at a measurable rate are considered to be under kinetic control-that is, their rate of progress is based on kinetics instead of thermodynamics.
|
Chemistry/72
|
Chemistry
| null |
What is the equilibrium expression for the reaction
A. \( K = \frac{[CO_2]^3}{[O_2]^5} \)
B. \( K = \frac{[C_3H_8][O_2]^5}{[CO_2]^3[H_2O]^4} \)
C. \( K = \frac{[C_3H_8]}{[H_2O]^4} \)
D. \( K = \frac{[O_2]^5}{[CO_2]^3} \)
|
A By convention, liquids are not written as part of the equilibrium law. Liquids always have the same number of molecules per liter, which is a constant, combined into the value of the K. The only nonsolid substances in this reaction are O$_2$(g) and CO$_2$(g). In this reaction, CO$_2$ to the third power appears in the numerator because it is a product, and O$_2$ to the fifth power is in the denominator.
|
Chemistry/73
|
Chemistry
| null |
Given the two standard reduction equations and their potentials below, write the thermodynamically favored chemical reaction and its standard cell potential.
A. $\text{Ag}^+ (\text{aq}) + \text{Mg}^{2+} (\text{aq}) \rightarrow \text{Ag}(\text{s}) + \text{Mg}(\text{s}) & -1.57\ V $
B. $\text{Ag}^+ (\text{aq}) + \text{Mg}(\text{s}) \rightarrow \text{Ag}(\text{s}) + \text{Mg}^{2+} (\text{aq}) & +3.17\ V$
C. $2\text{Ag}^+ (\text{aq}) + \text{Mg}(\text{s}) \rightarrow 2\text{Ag}(\text{s}) + \text{Mg}^{2+} (\text{aq}) & +3.17\ V$
D. $2\text{Ag}^+ (\text{aq}) + \text{Mg}(\text{s}) \rightarrow 2\text{Ag}(\text{s}) + \text{Mg}^{2+} (\text{aq}) & +3.97\ V$
|
C Only reactions (C) and (D) are balanced. Only reaction (C) simply subtracts -2.37 from +0.80 to get the correct +3.17 V.
|
Chemistry/74
|
Chemistry
| null |
In the diagram above, which labeled arrow is pointing toward a hydrogen bond?
A. 1
B. 2
C. 3
D. 4
|
C Dashed lines traditionally represent attractions that are NOT covalent bonds. In this case, they represent hydrogen bonds.
|
Chemistry/75
|
Chemistry
| null |
The graph above shows the distribution of kinetic energies of a large number of Ne atoms at 500 K. Which letter shows the average kinetic energy of this system?
A. A
B. B
C. C
D. D
|
C Slightly to the right of the maximum of the distribution curve is the average kinetic energy.
|
Chemistry/76
|
Chemistry
| null |
Consider the following possible mechanism for the reaction above: \[ \text{2SO}_2(g) + \text{O}_2(g) \rightarrow \text{2SO}_3(g) \] Consider the possible mechanism in the figure for the reaction above. Which of the following statements is true?
A. This mechanism has no free radicals.
B. \(\text{O}_2(g)\) is an intermediate.
C. \(\text{SO}(g)\) is a catalyst for this reaction.
D. The mechanism does not add up to the overall reaction.
|
A None of the structures has an odd number of electrons, which is necessary for a free radical.
|
Chemistry/77
|
Chemistry
| null |
Three 1-liter flasks are connected to a 3-liter flask by valves. The 3-liter flask is evacuated to start and the entire system is at 298K. The first flask contains helium, the second argon, and the third krypton. The pressure of the argon is 633 torr. The amounts of gas are proportional to their representations in the flasks. If all the valves to the center flask are opened, what will the pressure of the system be? Assume the connections have negligible volume.
A. 633 torr
B. 316 torr
C. 1266 torr
D. 211 torr
|
B The number of particles adds up to 18, and they are distributed in 6 liters of volume, giving 3 particles per liter. Since 6 particles per liter represents 633 torr, the pressure should be half of that, or 316 torr.
|
Chemistry/78
|
Chemistry
| null |
A portion of a mass spectrum of neon is presented above. Estimate the average mass of naturally occurring atoms of neon, assuming that the height of each line represents the relative amount of each mass.
A. 20.3
B. 20.0
C. 21.0
D. Not enough information is provided
|
A In this mass spectrum, we see about 90 percent of the atoms with a mass of 20, about 1 percent with a mass of 21, and 10 percent with a mass of 22. Calculate: (0.9)(20) + (0.01)(21) + (0.1)(22) = 18 + 0.2 + 2.2 = 20.4 for the average mass Since each mass was a little less than an integer value, 20.3 is reasonable.
|
Chemistry/79
|
Chemistry
| null |
The above graph shows a titration curve of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.075 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the graph. Which arrow points to the end point of this titration?
A. A
B. E
C. C
D. F
|
B Point E is the inflection point that represents the end point.
|
Chemistry/80
|
Chemistry
| null |
The above graph shows a titration curve of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.075 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the graph. Which arrow points to the place on the curve where the pH is equal to 14 - pK$_b$?
A. A
B. E
C. C
D. F
|
C Point C is the midpoint of the titration. At this point, the pOH = pK$_b$. The pOH = 14 - pH. So 14 - pH = pK$_b$, and this rearranges to the equation shown in the question.
|
Chemistry/81
|
Chemistry
| null |
The above graph shows a titration curve of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.075 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the graph. Find the two points on the curve that indicate the region where the solution can be described as a buffer. What is the change in pH from the first point to the second?
A. 0.5 pH unit
B. 1 pH unit
C. 2 pH units
D. 3 pH units.
|
C Points A and D represent the buffer region. Their pH difference is approximately 2 pH units.
|
Chemistry/82
|
Chemistry
| null |
The above graph shows a titration curve of a weak base titrated with a strong acid. The pH was measured with a pH meter after small volumes of 0.075 M HCl were added to 25.0 mL of a weak base. Data from that experiment are shown in the graph. Which of the following describes the base that is being titrated?
A. The base is dibasic since two end points are observed.
B. The concentration of the base is 0.075 $M$.
C. The concentration of the base is slightly more than 0.075 $M$.
D. The concentration of the base is slightly less than 0.075 $M$.
|
D The equation is M$_b$(25.0 mL) = (0.075 $M$)(22.5 mL). When solving for M$_b$, we see that 22.5/25.0 is less than 1. So the molarity of the base must be less than 0.075.
|
Chemistry/83
|
Chemistry
| null |
Refer to the figure. The Lewis electron-dot structures for sulfur trioxide and for the sulfite ion are given above. Which statement best describes the geometry of these two substances?
A. The sulfite ion has a triangular pyramid shape, and the sulfur trioxide is a planar triangle.
B. Both substances are flat, triangular, planar shapes.
C. Both substances are triangular pyramids.
D. SO$_3$ is a triangular pyramid, and SO$_3^{2-}$ is a planar triangle.
|
A Use the VSEPR theory and the fact that SO$_3$ has three domains (triangular planar) and that SO$_3^{2-}$ has four domains (tetrahedral domain structure and triangular pyramid molecular shape).
|
Chemistry/84
|
Chemistry
| null |
Refer to the figure. Which statement below describes the charge, polarity, and resonance characteristics of the sulfite ion and of the sulfur trioxide species shown above?
A. The sulfite ion has two negative charges along with a shape that makes it a dipole. Sulfur trioxide is symmetrical and nonpolar. In addition, as written, both have three resonance structures.
B. The sulfite ion and sulfur trioxide are both polar with the only difference being that one is an ion and the other is not.
C. Sulfur trioxide has three resonance structures, and the sulfite ion has no resonance structures.
D. Sulfite ions have a nonbonding electron pair domain, while sulfur trioxide has all electron domains as bonding domains.
|
B Both of the statements are true.
|
Chemistry/85
|
Chemistry
| null |
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