Question

Cortisone is a molecular substance containing $21$ atoms of carbon per molecule. The mass percentage of carbon in cortisone is $69.98 \%$. What is the molar mass of cortisone ?

• A. 176.5
• B. 252.2
• C. 287.6
• D. 360.1

Answer 1

Answer: (D)

In cortisone
$69.98 \,g C \equiv 100\, g$ cortison
$1$ mole of cortisone contains $21$ moles of carbon atoms or $252\, g$ of carbon
$252 \,g $ carbon $\equiv $ 1 mol cortisone
$69.98\, g$ carbon $\frac={69.98}{252}$ mol cortisone
$\frac{69.98}{252}$ mol cortisone $\equiv 100 \,g$
1mol cortisone $=\frac{100\,g \times 252}{69.98}=360.10\,g$
$\therefore $ Molar mass of cortisone $= 360.10 \,g\, mol^{-1}$