Hydrogen may be prepared in the laboratory by the action of a metal on an acid.
(a) Which of the metals copper, zinc , magnesium or sodium would be the most suitable ?
(b) Which of the acids dilute sulphuric, concentrated sulphuric, dilute nitric acid and concentrated nitric would you choose ? Explain why you would not use the acids you reject.
(c) How would you modify your apparatus to collect dry hydrogen ? Which drying agent would you employ for this purpose ?
(a) Among the given metals Zinc is most suitable.
(i) Copper: In case of copper, It is placed below hydrogen in the activity series. So it does not displace hydrogen from acid.
(ii) In case of Mg; it is a very expensive metal.
(iii) In case of sodium, it reacts with explosively and violently.
(b) Among the given acids we prefer dilute sulphuric acid.
We reject concentrated sulphuric, dilute nitric and concentrated nitric acid because these are powerful oxidising agents and oxygen formed due to its decomposition oxidises the hydrogen to water.
(c) Modification: Collect the gas by downward displacement of water when all the air from the apparatus has been expelled. Drying Agent used is Calcium Chloride.