impossible. However, we are going to see that chemists could use another tool the percent composition of – to determine molar masses. compounds Part 2: Relative Mass From Compound Data Many substances combine with oxygen to form a type of compound called an oxide. In the previous unit we saw that such combinations often occur in multiple proportions. John Dalton made the assumption that the lowest ratio was a 1:1 combination of elements. For now, we will make a similar assumption. We may have to re-examine this assumption later. Based on % composition data, the mass of each of the following elements that combines with 100 grams of oxygen was determined: Element Assumed Mass of element that relative Actual Dalton’s Compound combines with 100g mass (Question 4) relative mass Formula of oxygen (Question 5) Hydrogen HO 12.5 g 1.0 Carbon CO 75.0 Nitrogen NO 87.5 Oxygen O2 100 g Iron FeO 349 g Mercury HgO 1250 g Silver AgO 1349 g 3. If these elements combine in a 1:1 ratio, then the values in the 2nd column could be used to compare the masses of these elements. As you did in the relative mass lab, divide these values by the mass of hydrogen to obtain relative masses of the elements. Record these values in the 3rd column. These are the values Dalton reported for the masses of these elements. 4. a) Compare the value for the relative mass of oxygen and nitrogen you obtained this way to the value you calculated in Part 1: b) Why is assumption that H and O combined in a 1:1 ratio in water not justified? Dalton’s 5. Use the correct ratio of H and O atoms in water to determine the actual relative masses of these elements. How do these values compare to the molar masses in the Periodic Table? Are there any other elements in the table that do not combine in a 1:1 ratio? Explain.
impossible. However, we are going to see that chemists could use another tool – the percent composition of compounds to determine molar masses. Part 2: Relative Mass From Compound Data Many substances combine with oxygen to form a type of compound called an oxide. In the previous unit we saw that such combinations often occur in multiple proportions. John Dalton made the assumption that the lowest ratio was a 1:1 combination of elements. For now, we will make a similar assumption. We may have to re-examine this assumption later. Based on % composition data, the mass of each of the following elements that combines with 100 grams of oxygen was determined: Element Assumed Compound Formula Mass of element that combines with 100g of oxygen Dalton’s relative mass (Question 4) Actual relative mass (Question 5) Hydrogen HO 12.5 g 1.0 Carbon CO 75.0 Nitrogen NO 87.5 Oxygen O2 100 g Iron FeO 349 g Mercury HgO 1250 g Silver AgO 1349 g 3. If these elements combine in a 1:1 ratio, then the values in the 2nd column could be used to compare the masses of these elements. As you did in the relative mass lab, divide these values by the mass of hydrogen to obtain relative masses of the elements. Record these values in the 3rd column. These are the values Dalton reported for the masses of these elements. 4. a) Compare the value for the relative mass of oxygen and nitrogen you obtained this way to the value you calculated in Part 1: b) Why is Dalton’s assumption that H and O combined in a 1:1 ratio in water not justified? 5. Use the correct ratio of H and O atoms in water to determine the actual relative masses of these elements. How do these values compare to the molar masses in the Periodic Table? Are there any other elements in the table that do not combine in a 1:1 ratio? Explain.
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