b the excess reactant is vanished? Discuss removed nature of a solution. c the solution remaining is Ask students how they only salt and water could prove the salt was still there. How could C3.17 Investigate the preparation they get the salt back? of pure, dry, hydrated copper Demonstrate by sulfate crystals starting from evaporating water to copper oxide leave the salt. CC9d Alkalis and C3.10 Recall that alkalis are soluble 1) Ask the students to Students add successive Show the students a balancing bases predict the salts formed weighed portions of calcium simple balanced equations in the reaction between hydroxide powder to a fixed equation, e.g. NaOH + C3.11 …c) Explain the general some named metal amount of dilute hydrochloric HCl NaCl + H2O. reactions of aqueous oxides and common acid, and estimate the pH of Discuss why this is solutions of acids with metal acids. the reaction mixture using balanced, then show a hydroxides to produce salts. universal indicator paper. They more complex balanced 2) Demonstrate the then plot a graph of pH against equation, e.g. Mg(OH)2 C3.6 Investigate the change in pH addition of aluminium mass of calcium hydroxide + 2HCl MgCl2 + 2H2O. on adding powdered calcium oxide and calcium oxide added. Discuss why this is hydroxide or calcium oxide to powders to water. The pH will increase as more balanced, including the a fixed volume of dilute Aluminium oxide is calcium hydroxide is added, use of OH and H to hydrochloric acid insoluble so the mixture with the end-point at produce water when will remain green. approximately 1.85 g of calcium balancing; and keeping Calcium oxide reacts with oxide. Calcium hydroxide is NO3, SO4 and PO4 as water to produce calcium sparingly soluble (about 0.17 units when balancing hydroxide, which g/100 cm3 H2O) so beyond this (rather than counting dissolves to form an excess calcium hydroxide will their atoms separately). alkaline solution so the be seen. Show unbalanced mixture turns purple. alkali/acid equations Equipment: eye protection; and work through Equipment: eye 100 cm3 beaker; 50 cm3 balancing with the protection; test tube measuring cylinder; ±0.1 g students.
C3.17 b the excess reactant is removed c the solution remaining is only salt and water Investigate the preparation of pure, dry, hydrated copper sulfate crystals starting from copper oxide vanished? Discuss nature of a solution. Ask students how they could prove the salt was still there. How could they get the salt back? Demonstrate by evaporating water to leave the salt. CC9d Alkalis and balancing equations C3.10 C3.11 C3.6 Recall that alkalis are soluble bases …c) Explain the general reactions of aqueous solutions of acids with metal hydroxides to produce salts. Investigate the change in pH on adding powdered calcium hydroxide or calcium oxide to a fixed volume of dilute hydrochloric acid 1) Ask the students to predict the salts formed in the reaction between some named metal oxides and common acids. 2) Demonstrate the addition of aluminium oxide and calcium oxide powders to water. Aluminium oxide is insoluble so the mixture will remain green. Calcium oxide reacts with water to produce calcium hydroxide, which dissolves to form an alkaline solution so the mixture turns purple. Equipment: eye protection; test tube Students add successive weighed portions of calcium hydroxide powder to a fixed amount of dilute hydrochloric acid, and estimate the pH of the reaction mixture using universal indicator paper. They then plot a graph of pH against mass of calcium hydroxide added. The pH will increase as more calcium hydroxide is added, with the end-point at approximately 1.85 g of calcium oxide. Calcium hydroxide is sparingly soluble (about 0.17 g/100 cm3 H2O) so beyond this excess calcium hydroxide will be seen. Equipment: eye protection; 100 cm3 beaker; 50 cm3 measuring cylinder; ±0.1 g Show the students a simple balanced equation, e.g. NaOH + HCl NaCl + H2O. Discuss why this is balanced, then show a more complex balanced equation, e.g. Mg(OH)2 + 2HCl MgCl2 + 2H2O. Discuss why this is balanced, including the use of OH and H to produce water when balancing; and keeping NO3, SO4 and PO4 as units when balancing (rather than counting their atoms separately). Show unbalanced alkali/acid equations and work through balancing with the students.