Question

A metal sulphate has the formula \[MS{O_4}\]. A chloride of the same metal will have the formula.
A. \[{M_2}C{l_3}\]
B. \[{M_2}Cl\]
C. \[MC{l_2}\]
D. \[MCl\]

Answer 1

Hint: From the formula of metal sulphate we come to know that the valency of the metal M will be +2 because the valency of the sulphate ion is always -2. For metal chloride, chlorine has valency of -1, this can help in predicting the chemical formula for metal chloride.

Complete step-by-step answer:
The valency determines the combining capacity of an element so as to form a compound. If any two elements have the same valency, then one atom of each will combine to form the product. For the formation of an ionic compound, the two elements which will combine to form the ionic compound will either lose or gain the same number of electrons as their oxidation number or valency.
The electropositive element loses electrons while the electronegative elements will gain electrons. For metal sulphates, sulphate has a negative charge on it i.e., -2. From this we know that the metal combined has a valency of +2, since it is a neutral compound. Similarly, for metal chlorides we know that chloride carries a negative charge, therefore two chlorine atoms will result in -2 charge. In this way metal will react with two chlorine atoms to form metal chloride.
 \[{M^{2 + }} + 2C{l^{^ - }} \to MC{l_2}\]

Hence, the correct option is (C).

Note: We might confuse valency with oxidation state. Valency is the number of electrons an element can lose or gain to form a compound whereas the oxidation state is the number of electrons an element has already gained or lost after formation of a specific compound.