Question

Write chemical equations for the five reactions described:

The first reaction involves the oxidation of copper with nitric acid, resulting in a blue-green colored copper (II) nitrate, Cu(NO3)2, solution.

The second reaction involves adding sodium hydroxide. This results in a double replacement or precipitation reaction produces a milky-blue copper (II) hydroxide solid.

The third reaction involves decomposition of the of the hydroxide compound to a black copper (II) oxide solid while applying heat.

After filtering the oxide, sulfuric acid is added to the solid to produce a blue copper (II) sulfate solution in a double replacement, or more specifically an acid-base reaction.

Finally, solid elemental copper is recovered through a single replacement reaction by the addition of zinc metal filings.

Answer 1

1)Cu is oxidised when reacted with nitric acid. Nitrogen monoxide gas is formed on reaction of Cu with dilute nitric acid (HNO₃) while nitrogen dioxide gas(NO₂)is formed when Cu is reacted with concentrated HNO₃.Equation Both the equation are given below:

3Cu(s) +8HNO₃(aq) - - - - >3Cu(NO₃)₂(aq) +2NO(g) +4H₂O(l)

Cu(s)+4HNO₃(aq) - - - - >Cu(NO₃)₂(aq)+2NO₂(g)+2H₂O(l)

In this reaction, nitric acid is an oxidizing agent because it oxidises Cu to Cu²⁺(in Cu(NO₃)₂. The increase in oxidation state indicates that copper lost 2 electrons as its oxidation state changes from 0 (in Cu) to +2 in Cu(NO₃)_2. Since loss of electrons is an oxidation. Thus, Cu is oxidised.

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

The exchange of ions between two compounds is called double displacement reaction. In this reaction, a milky blue Copper (II) hydroxide is formed. Hydroxides are insoluble except group 1 like Na⁺​​​​​​, K⁺​​​​​​etc. NH₄⁺, Ca²⁺,Sr²⁺.Thus, in accordance with solubility rules, NaOH is soluble while copper hydroxide is insoluble. All nitrates are soluble. Thus, both copper nitrate and sodium nitrate exists as aqueous solution.

3)Cu(OH)₂(s)------^heat--->CuO(s)+H₂O(l)

CuO, a black solid, is formed on decomposition of copper hydroxide. Heating copper hydroxide removes a molecule of water leaving behind black solid.

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

The above reaction is double displacement or acid base reaction. As metallic oxides are basic in nature, CuO is basic. When reacted with acid, a salt ( blue colored copper sulfate) and water is formed. Thus, it is a acid-base neutralization reaction.

5)CuSO₄(aq)+Zn(s)---->Cu(s)+ZnSO₄(aq)

This is a single displacement reaction in which more reactive metal Zn displaces less reactive metal Cu from its solution. This changes the color of solution from blue to colorless.