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Question: The salt of an oxyacid of a metal M contains one M, one sulphur and four oxygen atoms. The valency o...

The salt of an oxyacid of a metal M contains one M, one sulphur and four oxygen atoms. The valency of metal M is
A. 00
B. 22
C. 33
D. 44

Explanation

Solution

An oxyacid is a type of acid which consists of an oxygen atom bonded to a hydrogen atom and at least one other element than hydrogen and oxygen. The general structure of an oxyacid is X−O−HX - O - H and it dissociates into water to release protons and form respective anions of the acid. Most common examples are sulphuric acid, phosphoric acid, etc.

Complete answer:
As per question, it is given that the oxyacid consists of one metal M, one sulphur and four oxygen atoms. So, assume the formula of oxyacid is MSO4MS{O_4}.
As it is a neutral molecule, so the total valency of the compound is zero. Let the valency of the considered metal ion i.e., M be x. We know that the sulphur atom generally exists in its +6 + 6 valency and the oxygen atom usually form compounds with a valency of −2 - 2. Therefore, the valency of M can be calculated as follows:
x+6+4×(−2)=0x + 6 + 4 \times ( - 2) = 0
⇒x=+2\Rightarrow x = + 2
Hence it is a bivalent metal ion and has a valency of +2 + 2. So, option (B) is the correct answer.

Additional information-
As we know the valency of the metal atom, so we can determine the base formula of the oxyacid as follows:
Let the base formula of oxyacid is Ma(OH)b{M_a}{(OH)_b}. As it is a neutral molecule so overall valency is zero. Therefore, the relation between a and b can be calculated as follows:
2a+b(1−2)=02a + b(1 - 2) = 0
⇒2a−b=0\Rightarrow 2a - b = 0
⇒b=2a\Rightarrow b = 2a
Substituting the value of b in the formula assumed:
⇒Ma(OH)2a\Rightarrow {M_a}{(OH)_{2a}}
Hence, the base formula of the oxyacid is M(OH)2M{(OH)_2}.

Note:
It is important to note that ketones and oxocarboxylic acids are sometimes also referred to as oxyacids. Also, the dissociation of an oxyacid depends upon the electronegativity of the X atom considered. If X is strongly electronegative, then it will dissociate to give protons whereas if it has low electronegativity, then the acid will dissociate to give hydroxide ions.