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 separate test tubes.

Dilute HCl is added to one part of substance B and dilute HNO₃ 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 dilute hydrochloric acid ? Give reasons for your answer.

(a) A = copper oxide [CuO],
B = copper [Cu]

(b) The liquid does not change the colour of blue or red litmus paper, showing neutral nature.

It changes the colour of cobalt chloride paper from blue to pink colour. Hence, the liquid produced is water.

(c) Black copper oxide (A) is reduced to copper, by losing oxygen. This happens because, hydrogen, the reducing agent reduces copper oxide to copper.

(d) CuO + H₂ $\xrightarrow{\Delta}$ Cu + H₂O

(e) As copper is less reactive than hydrogen and lies below it in the metal reactivity series, hence it cannot displace it from HCl. Hence, there is no reaction between them.

Cu + HCl ⟶ No reaction