Question

Which of the following metals would give hydrogen when added to dilute hydrochloric acid:-
1) Iron
2) Copper
3)Magnesium
Explain why do surfaces of some metals acquire a dull appearance when exposed to air for long time?

Answer 1

Answer:

iron and magnesium will liberate hydrogen gas when reacting with dilute hydrochloric acid where is copper will not.

this is because according to the reactivity series of metals iron and magnesium are more reactive than hydrogen where is copper is less reactive and hence iron and magnesium liberate hydrogen gas easily but copper will not.

surfaces of some metals acquire a dull appearance when exposed to air for long time. This is because they react with oxygen present in the air and form oxides.

Answer 2

Explanation:

(a) Both iron (Fe) and magnesium (Mg) will evolve hydrogen on reacting with dilute hydrochloric acid. These are active metals and are placed above hydrogen in the activity series. As copper is placed below hydrogen in the series, it will not evolve hydrogen.

(b) Surfaces of some metals acquire a dull appearance when exposed to air for a long time and they lose their lustre. This is due to the formation of layer of oxides, hydroxides, carbonates etc. on the surface. For example, surface of aluminium metal becomes dull white due to the formation of coating of aluminium oxide (Al2O3). Similarly, the surface of copper acquires a greenish colour since a layer of basic copper carbonate with the formula Cu(OH)2CuCO3 is deposited on the surface.