Question

By reference to the Cu cycle lab experiment, identify the false statements among the following: i) Metallic copper reacts with nitric acid but not with hydrochloric acid because CuCl2 is insoluble in water whereas Cu(NO3)2 is soluble. ii) When copper reacts with nitric acid, both nitrogen dioxide and hydrogen gas are produced. iii) Copper does not react with hydrochloric acid but does with nitric acid because the latter is a stronger oxidizing agent. iv) When Zn reacts with nitric acid, the only gas produced is hydrogen gas. v) Metallic Zn is a stronger reducing agent than metallic copper.

Answer 1

Statement (ii) is false. This is because metallic Cu reacts with HNO3 to liberate only nitrogen dioxide gas. Actually this reaction is not an usual acid-metal reaction. As Cu lies below H in the electrochemical series Cu cannot displace H readily from any dilute acid. But in case of HNO3, as it is a strong oxidising agent it can oxidise Cu to Cu2+. Thus the NO3- anion can dissolve Cu2+ forming Cu(NO3)2 and byproduct NO2. This is a normal oxidation-reduction type of reaction.The reaction is shown below.