Question

1.The Cu2+ ions in this experiment are produced by the reaction of 1.0g of copper turnings with excess nitric acid. How many moles of Cu2+ are produced?

2. Why isn't hydrochloric acid used in a direct reaction with copper to prepare the CuCl2 solution?

3. How many grams of metallic copper are required to react with the number of moles of Cu2+ calculated in Problem 1 to form the CuCl? The overall reaction can be taken to be: Cu2+(aq) + 2Cl-(aq) + Cu(s) -----> 2CuCl(s)

4. What is the maximum mass of CuCl that can be prepared from the reaction sequence of this experiment, using 1.0g of Cu turnings to prepare the Cu2+ solution?

5. A sample of the compound prepared in this experiment , weighing 0.1021g, is dissolved in HNO3, and diluted to a volume of 100 ml. A 10ml aliquot of that solution is mixed with 10 mL 6M NH3. The [Cu(Nh3)4]2+ in the resulting solution is found to be 5.16 x 10^-3 M.

a. How many moles of Cu were in the original sample, which had been effectively diluted to a volume of 200 mL.

b. How many grams of Cu were in the sample?

c. How many grams of Cl were in the sample? How many moles?

d. What is the formula of the copper chloride compound?

Answer 1

1: Given the mass of Cu = 1.0 g

Atomic mass of Cu = 63.54 g/mol

Hence moles of Cu = mass / atomic mass = 1.0 g / 63.54 g/mol = 0.01574 mol

When copper reacts with excess HNO3, all of the copper is converted to Cu2+.

Hence moles of Cu2+ formed = 0.01574 mol

2: hydrochloric acid is not used in the preparation of CuCl2 solution, because HCl is unable to oxidise copper due to high reduction potential.

3: Moles of Cu2+(aq) calculated in problem-1 = 0.01574 mol

The given balanced chemical reaction is

Cu2+(aq) + 2Cl-(aq) + Cu(s) -----> 2CuCl(s)

1 mol 2 mol 1 mol 2 mol

In the above balanced reaction 1 mol of Cu2+(aq) reacts with 1 mol of metallic Cu

Hence moles of metallic Cu that will react with 0.01574 mol of Cu2+(aq)

= 0.01574 mol Cu2+ x (1 mol metallic Cu / 1 mol Cu2+) = 0.01574 mol metallic Cu.

Molecular mass of Cu = 63.54 g/mol

Hence mass of metallic Cu required = 0.01574 mol x 63.54 g/mol = 1 g (answer)

4: In the above balanced reaction 1 mol of Cu2+(aq) forms 2 mol CuCl(s)

Hence moles of CuCl(s) that will be formed from 0.01574 mol of Cu2+(aq)

= 0.01574 mol Cu2+ x (2 mol CuCl(s) / 1 mol Cu2+) = 0.03148 mol CuCl(s)

Molecular mass of CuCl(s) = 99 g/mol

Hence maximum mass of CuCl(s) formed = 0.03148 mol x 99 g/mol = 3.116 g (answer)