Question

A newly discovered metalloprotein, which contains three atoms of mg per molecule of protein, is found to be 0.672% mg by mass. calculate the molar mass of the metalloprotein.

Answer 1

Mass percentage is given as:

$Mass percentage = \frac{mass of element}{total mass of the compound}\times 100$%

Let the total mass of protein = 100 g.

Mass percentage of $Mg$ in protein = 0.672%

That means 0.672 g of $Mg$ is present in 100 g of protein.

Atomic mass of $Mg$ = 24.305 u

Number of moles = $\frac{mass}{Molar mass}$

Number of moles of $Mg$ = $\frac{0.672}{24.305} = 0.028 mol$

Since, 1 molecule of protein contains 3 atoms of $Mg$ so, moles of protein is:

Moles of protein = $\frac{0.0028}{3} = 0.0093 mol$

Rearranging the formula of number of moles as:

$Molar mass = \frac{mass}{mole}$

Substituting the values:

Molar mass of protein = $\frac{100 g}{0.0093 mol}$

Molar mass of protein = $10752.69 g/mol$

Hence, the molar mass of metalloprotein is $10752.69 g/mol$.