Question

When hydrogen is passed over a black solid compound A , the products are 'a colourless liquid' and 'a reddish brown metal B.'

Substance B is divided into two parts, each placed in seperate test tubes.

Dilute HCI is added to one part of substance B and dilute $HN{O}_3$ to the other.

(a) Name the substances A and B.

(b) Give two tests for the colourless liquid formed in the experiment.

(c) What happens to substance A when it reacts with hydrogen ? Give reasons for your answer.

(d) Write an equation for the reaction between hydrogen and substance A.

(e) Is there any reaction between substance B and silute hydrochloric acid ? Give reasons for your answer.

Answer 1

(a) Substance A is CuO and substance B is Cu.

(b) Test for water
(i) It is neutral to litmus
(ii) It changes anhydrous copper sulphate into blue salt.

(c) When substance A i.e, CuO reacts with hydrogen, it removes oxygen and we get free metal i.e. Cu.

(d) CuO + H₂ → Cu + H₂O

(e) No, there is no reaction between substance B and dilute hydrochloric acid because copper does not displace hydrogen from acids.

(f) Cu + HCl → No reaction