Question

Equivalent mass of a bivalent metal is 32.7. Molecular mass of its chloride is
$
  (a)68.2 \\
  (b)103.7 \\
  (c)136.4 \\
  (d)4166.3 \\
 $

Answer 1

Hint – In this question use the concept that charge on a bivalent metal is 2, thus compute the molar mass of the metal and it will be twice multiplied with equivalent mass of bivalent metal. The compound must have 2 atoms of chloride so write the chemical formula of its chloride and use the mass of chloride as 35.5 to get the answer.

Complete answer:

Given data:
Equivalent mass on the bivalent metal = 32.7.
As it is given that the metal is bivalent, so the charge on the metal = 2.
Therefore the molar mass of the metal = $2 \times 32.7 = 65.4$
Now we have to find out the molecular mass of its chloride.
As the charge on the metal = 2.
Therefore there are 2 atoms of chloride present in the chemical formula.
So the chemical formula = MCl2, where M is the symbol for the metal.
Now as we know that the mass of the chloride (Cl) = 35.5.
So the molecular mass of its chloride = $65.4 + 2\left( {35.5} \right) = 65.4 + 71 = 136.4$.
So this is the required answer.
Hence option (C) is the correct answer.

Note – The trick point in this question is to get the chemical formula of the compound. The total mass of a compound is always the sum of the masses of its individual components. It is always advised to remember the mass of some basic elements like ${\text{mass of }}N{\text{ }} = {\text{ }}14,{\text{ }}H{\text{ }} = {\text{ }}1,{\text{ }}P{\text{ }} = {\text{ }}31{\text{ and }}O{\text{ }} = 16$ as it helps solving problems of this kind.