This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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You're on a roll — here are the solutions to the questions. Question 9: Extraction of Zinc a) The process used in step 2 to concentrate the ore is froth flotation (or gravity separation). Froth flotation b) The reaction that takes place in step 3 is the thermal decomposition of zinc carbonate to zinc oxide and carbon dioxide. ZnCO_3(s) heat ZnO(s) + CO_2(g) c) One use of zinc other than galvanizing is in the production of alloys (e.g., brass) or dry cell batteries. Alloys (e.g., brass) Question 10: Sequence of Copper Reactions a) In step 1, excess 3M nitric acid was added to 0.5g of copper powder. (i)* Two observations made were: • The reddish-brown copper powder dissolves, and the solution turns blue. • A brown gas is evolved. (ii) Dilute hydrochloric acid cannot be used in step 1 because copper is less reactive than hydrogen* and therefore cannot displace hydrogen from hydrochloric acid. Hydrochloric acid is also a non-oxidizing acid. (iii)* I. The equation for the reaction in step 1 is: Cu(s) + 4HNO_3(aq) Cu(NO_3)_2(aq) + 2NO_2(g) + 2H_2O(l) (iii)* II. Calculate the volume of 3M nitric acid needed. Step 1: Calculate moles of copper. Moles of Cu = MassMolar mass = 0.5 g63.5 g/mol ≈ 0.007874 mol Step 2: Use stoichiometry to find moles of nitric acid. From the equation, 1 mol Cu reacts with 4 mol HNO_3. Moles of HNO_3 = 4 × Moles of Cu = 4 × 0.007874 mol ≈ 0.031496 mol Step 3: Calculate the volume of nitric acid. Volume of HNO_3 = MolesConcentration = 0.031496 mol3 mol/dm^3 ≈ 0.010499 dm^3 Converting to cm^3: Volume of HNO_3 = 0.010499 dm^3 × 1000 cm^3/dm^3 ≈ 10.5 cm^3 10.5 cm^3 b) The names of the types of reactions that took place in steps 4 and 5 are: Step 4: CuO(s) + 2HCl(aq) CuCl_2(aq) + H_2O(l) is an acid-base reaction* (or neutralization). Step 5: Cu^2+(aq) + Metal Q(s) Cu(s) + Q^2+(aq) is a displacement reaction*. Step 4: Acid-base reaction, Step 5: Displacement reaction c) Apart from good conductivity of electricity, two other properties of copper that make it suitable for the electrical industry are: • Ductility (can be drawn into wires). • Malleability (can be hammered into sheets). Question 11: Investigation of Temperature Changes a) Two factors that must be kept constant in this experiment are: • Initial temperature of the acid and sodium hydroxide solutions. • Concentration of the acid and sodium hydroxide solutions. • Volume of the acid. b) The use of a polystyrene cup will reduce heat loss to the surroundings because polystyrene is a good thermal insulator. This will lead to a more accurate measurement of the temperature change. Question 12: Molar Heat of Displacement and Energy Level Diagram a) The molar heat of displacement is the enthalpy change when one mole of a metal is displaced from its salt solution by a more reactive metal. b) The reaction Z^2+(aq) + Y(s) Z(s) + Y^2+(aq) has H = -ve, meaning it is an exothermic reaction. The energy level diagram for an exothermic reaction shows the products at a lower energy level than the reactants. [->] (0,0) -- (0,4) node[above] Energy; [->] (0,0) -- (4,0) node[right] Reaction progress; [thick] (0.5,3.5) -- (1.5,3.5) node[right] Reactants: Z^2+(aq) + Y(s); [thick] (2.5,1.5) -- (3.5,1.5) node[right] Products: Z(s) + Y^2+(aq); [<->, dashed] (1.5,3.5) -- (2.5,1.5) node[midway, right] H = -ve; Got more? Send 'em!