9701 MCQ Solution 13

Question 13: [Inorganic > Period 3]:

The chloride of element Q is hydrolysed by water to form an acidic solution and its oxide reacts with acid to form a salt.

What could be the element Q?

A magnesium

B aluminium

C silicon

D phosphorus

Reference: Past Exam Paper – November 2002 Paper 1 Q13

Solution 13:

Answer: B.

The best way forward is to focus on the second part of the question. If the oxide reacts with an acid it must be either basic or amphoteric. This eliminates option C because silicon(IV) oxide is a giant molecular structure that does not react. It also eliminates option D since phosphorous can only make acidic oxides since it is a non-metal. 

Magnesium chloride is hydrolysed by water to form an almost neutral solution, due to slight disassociation of H₂O into ions. 

However Aluminium chloride disassociates in water to form hydrochloric acid, hence option B is the “more” correct answer.