Chemistry
State why hydrogen is not prepared in the laboratory by the action of –
(a) Sodium with cold water.
(b) Calcium with dilute sulphuric acid.
(c) Lead with dilute hydrochloric acid.
Answer
(a) Sodium is very reactive and reacts with water violently. It melts into a globule and darts about in water. Hence, the collection of hydrogen is difficult using sodium and cold water.
(b) As the reaction between calcium and dil. sulphuric acid is highly explosive and practically not feasible, hence, hydrogen is not prepared in the laboratory by the action of calcium with dilute sulphuric acid.
(c) Lead reacts with dilute hydrochloric acid forming an insoluble coating of lead chloride (PbCl2) and hence, further reaction comes to a stop. Therefore, hydrogen is not prepared in the laboratory by the action of lead with dilute hydrochloric acid.
Related Questions
Give balanced equations for obtaining hydrogen from cold water using –
(a) A monovalent active metal
(b) A divalent active metal
Give balanced equations for obtaining hydrogen from ?
(a) Boiling water using a divalent metal
(b) Steam using a trivalent metal
(c) Steam using a metal – and the reaction is reversible.
Give balanced equations for the following conversions.
(a) Sodium zincate from zinc
(b) Sodium plumbite from lead
(c) Sodium aluminate from aluminium.
In the laboratory preparation of hydrogen from zinc and dil. acid. Give reasons for the following :
(a) The complete apparatus is air-tight.
(b) Dilute nitric acid is not preferred as the reactant acid.
(c) The lower end of the thistle funnel should dip below the level of the acid in the flask.
(d) Hydrogen is not collected over air.