Chemistry
Why are the following metals not used in the lab. preparation of hydrogen?
(a) calcium
(b) iron
(c) aluminium
(d) sodium
Answer
The following metals are not used in the lab. preparation of hydrogen because:
(a) Calcium is expensive.
(b) Iron has to be heated, but then the hydrogen thus produced contains impurities like hydrogen sulphide and sulphur dioxide.
(c) Aluminium forms a protective coating of Al2O3 due to its great affinity for oxygen. Due to the coating of Al2O3, aluminium does not give hydrogen with acid.
(d) Sodium reacts violently with acid.
Related Questions
Which metal is preferred for preparing hydrogen from:
(a) cold water?
(b) hot water?
(c) steam?
Write balanced equation for each case.
Hydrogen may be prepared in the laboratory by the action of a metal with 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 and concentrated nitric would you choose? Explain why you would not use the acids you rejected.
(c) How would you modify your apparatus to collect dry hydrogen? Which drying agent would you employ for this purpose?
Based on the reactions of water on metals, arrange the following metals in increasing order of reactivity: Iron, sodium, magnesium, zinc, calcium.
Hydrogen is evolved when dilute HCl reacts with magnesium, but nothing happens in the case of mercury and silver. Explain.