Question

Identify the following terms / compounds:
(a) A compound which reacts with water to give acetylene gas.
(b) The gas evolved when sodium propanoate is heated with soda lime.
(c) A reddish-brown precipitate formed when ferric chloride solution reacts with an alkali.
(d) A pair of electrons present in an atom which is not shared with any other atom during bond formation.
(e) The relative molecular mass of a substance expressed in grams.

Hint:

When using soda lime for decarboxylation, the resulting alkane always has one carbon atom less than the starting carboxylic acid salt. This is why sodium propanoate (C_3) yields ethane (C_2).

Answer 1

(a) The compound is calcium carbide (CaC₂).
It reacts with water to produce acetylene gas.

(b) The gas evolved is ethane (C₂H₆).
Sodium propanoate on heating with soda lime undergoes decarboxylation and forms ethane.

(c) The reddish-brown precipitate is ferric hydroxide [Fe(OH)₃].

(d) The pair of electrons is called a lone pair of electrons or non-bonding electron pair.

(e) The relative molecular mass of a substance expressed in grams is called gram molecular mass or molar mass.