Final answer:
HNO₃ is added to the potassium nitrate and copper sulfate mixture primarily for promoting oxidation. It serves as an oxidizing agent to transform copper compounds into soluble forms, as illustrated by reactions where copper compounds react with nitric acid. The correct option is A) Promoting oxidation.
Step-by-step explanation:
HNO₃ (nitric acid) is added to a mixture of potassium nitrate and copper sulfate primarily for promoting oxidation. This is because nitric acid is a strong oxidizing agent and can oxidize other substances in a chemical reaction.
When nitric acid reacts with copper, for example, it can produce copper nitrate and nitrogen dioxide, as seen in the reaction where copper metal reacts with concentrated HNO₃.
Relevant Reactions:
- Copper (II) oxide and nitric acid reaction: CuO(s) + 2 HNO₃(aq) → Cu(NO₃)₂(aq) + H₂O(l) - This produces soluble copper nitrate.
- Oxidation of copper sulfide by nitric acid: CuS(s) + 2H⁺(aq) + 2 NO₃⁻(aq) → Cu²⁺(aq) + 2 NO(g) + SO₄²⁻(aq) - This converts sulfide to sulfate while nitric acid is reduced to nitrogen monoxide.
By undergoing these reactions, HNO₃ assists in the dissolution and transformation of copper compounds. The examples given demonstrate HNO₃'s role as an oxidizer and why it would be added to the given mixture to either dissolve copper compounds or transform them into more stable, soluble forms.