Question

An element "X" of valency 3 forms oxide with chemical formula $X_2{O}_3$. Find:
(i) the ions present in the compound.
(ii) the chemical formula of its chloride.
(iii) the chemical formula of its sulphide.
[5 Marks]

Answer 1

(i) Given that the chemical formula of oxide containing element X is $X_2{O}_3$ and the valency of X is 3.
Thus, the ions present in the compound are : $X^{3+}$ and $O^{2-}$

[1 Mark]

(ii) Valency of $X^{3+}$ = 3
Valency of ${Cl}^{-}$ = 1

Upon criss-crossing the valancies:

Symbol	X	Cl
Valency	3	1

The chemical formula of the chloride is ${XCl}_3$.

[2 Marks]

(iii) Valency of $X^{3+}$ = 3
Valency of $S^{2-}$ = 2

Upon criss-crossing the valencies,

Symbol	X	S
Valency	3	2

The chemical formula of the sulphide is $X_2{S}_3$.

[2 Marks]