Question

Formula unit mass of magnesium chloride is:
a.) 94
b.) 95
c.) 96
d.) 24

Answer 1

Hint: The formula unit mass is the sum of the atomic masses of all the elements present in the corresponding compound. Now, the chemical formula of magnesium chloride is MgCl$_2$.

Complete step by step answer:
Firstly, let us define the formula unit mass. The formula unit mass can be defined as the sum of atomic masses of all atoms in the compound, and the formula unit is used for the substances made up of ions.
Now, we are given with the compound i.e. magnesium chloride having the chemical formula MgCl$_2$. The atomic mass of magnesium is 24 u, whereas chlorine has the atomic mass 35.5 u.
Now, the formula unit mass of magnesium chloride is equal to atomic mass of magnesium added with the atomic mass of two units of chlorine. It can be represented as: formula unit mass of MgCl$_2$ = atomic mass of Mg + 2$\times$atomic mass of Cl
After substituting the value of masses, we get formula unit mass = 24 u+2$\times$35.5 u=95 u
Therefore, the formula unit mass of magnesium chloride is 95 u. The correct option is B.

Note: Don’t get confused between the atomic mass unit and formula unit mass. While calculating the formula unit mass we multiplied the atomic mass of chlorine by 2 as in the chemical formula we can see there are 2 units of chlorine.