Question

A compound contains $6.4\%$ by mass of oxygen. What is the minimum molar mass of the compound?

• A. $500gmo{l}^{-1}$
• B. $250gmo{l}^{-1}$
• C. $333.33gmo{l}^{-1}$
• D. $125gmo{l}^{-1}$

Answer 1

The correct option is B $250gmo{l}^{-1}$

If we take the basis as 100 g of the compound, $6.4\%$ by mass oxygen means that it contains $6.4g$ of oxygen.
The compound has to have at most 1 atom of oxygen for us to find out the minimum molar mass.
So, 1 atom or $16g$ of oxygen is present which is $6.4\%$ of the molar mass of compound.
$\frac{6.4}{100}\times M=16gmo{l}^{-1}$
where, $M$ is the molar mass of compound
So, $M=250gmo{l}^{-1}$