Question

3) The following “cycle of copper” experiment is performed in some general chemistry laboratories. The series of reactions starts with copper wire and ends with metallic copper. The steps are as follows:

I. A piece of copper wire of known mass is allowed to react with concentrated nitric acid, the products are copper(II) nitrate , nitrogen dioxide, and water.

II. The copper(II) nitrate is treated with a sodium hydroxide solution to form copper(II) hydroxide.

III. On heating, the copper(II) hydroxide decomposes to yield copper(II) oxide.

IV. The copper(II) oxide is combined with concentrated sulfuric acid to yield copper(II) sulfate.

V. Copper(II) sulfate is treated with excess solid zinc metal to form metallic copper.

VI. The remaining zinc metal is treated with hydrochloric acid, and metallic copper is filtered, dried, and weighed.

a. Write a balanced chemical equation for each step. Be sure to pay attention to phase labels.

b. Classify each reaction as a precipitation, acid-base, or redox reaction.

c. Assuming that a student started with 65.6 g of copper, calculate the theoretical yield for each step

Answer 1

a. Write a balanced chemical equation for each step. Be sure to pay attention to phase labels.

I. A piece of copper wire of known mass is allowed to react with concentrated nitric acid, the products are copper(II) nitrate , nitrogen dioxide, and water.

Cu(s) + HNO3(aq) --> Cu(NO3)2(aq) + NO2(g) + H2O(l)

this is redox

II. The copper(II) nitrate is treated with a sodium hydroxide solution to form copper(II) hydroxide.

Cu(NO3)2(aq) + 2NaOH(aq) --> Cu(OH)2(aq) + 2NaNO3(aq)

this is acid base (lewis)

III. On heating, the copper(II) hydroxide decomposes to yield copper(II) oxide.

Cu(OH)2(s) --> CuO(s) + H2O(g)

this is redox

IV. The copper(II) oxide is combined with concentrated sulfuric acid to yield copper(II) sulfate.

CuO(s) + H2SO4(aq) --> CuSO4(aq) + H2O(l)

this is double replacement

V. Copper(II) sulfate is treated with excess solid zinc metal to form metallic copper.

CuSO4(aq) + Zn(s) --> Cu(s) + ZnSO4(aq)

this is redox

VI. The remaining zinc metal is treated with hydrochloric acid, and metallic copper is filtered, dried, and weighed.

Zn+2(aq) + HCl(aq) --> ZnCl2(aq) + H2(g);

this is redox

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