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) A compound which reacts with water to give acetylene gas: 
Calcium Carbide (CaC_2). 
The reaction is: CaC_2 + 2H_2O Ca(OH)_2 + C_2H_2uparrow 

(b) The gas evolved when sodium propanoate is heated with soda lime: 
Ethane (C_2H_6). 
This is a decarboxylation reaction: C_2H_5COONa + NaOH xrightarrowCaO, Delta C_2H_6 + Na_2CO_3. 

(c) A reddish-brown precipitate formed when ferric chloride solution reacts with an alkali: 
Ferric Hydroxide [Fe(OH)_3]. 
The reaction with sodium hydroxide is: FeCl_3 + 3NaOH Fe(OH)_3downarrow + 3NaCl. 

(d) A pair of electrons present in an atom which is not shared with any other atom during bond formation: 
Lone pair (or unshared pair). 

(e) The relative molecular mass of a substance expressed in grams: 
Gram Molecular Mass (or one mole).