Question

A chloride salt MCl2 is 63.89% chlorine by mass. What is the identity of M?

Please explain steps

Answer 1

Given that;

A chloride salt MCl2 is 63.89% chlorine by mass

Cl has an atomic mass of 35.5 g/mol and given that Cl takes up 63.89% of the total mass of the compound, we can find the total mass of the compound:
Here two Cl atoms are present.

(35.5 g/mol *2) / total mass of compound =63.89%

(35.5 g/mol *2) / total mass of compound =63.89/100

total mass of compound =35.5 g/mol *2 / 0.6389

total mass of compound = 111.13 g/mol

So the unknown compound has a total mass of 111.13 g/mol. Since we know that there is 2 Cl atoms the mass of the metal is 111.13 – 71.0 = 40.13 g/mol. Now look on to the periodic table and look for an element with a mass that is close to 40.13 g/mol, and we see that it is Ca.

Hence the compound is CaCl2.