Question

An organic compound of molar mass greater than $100gmo{l}^{-1}$ contains only $C$, $H$ & $N$. The mass of $C$ is six times the mass of $H$, while the sum of mass of $C$ & $H$ is 1.5 times the mass of $N$.Then $\frac{\text{Least molecular mass}}{28}$ is

Answer 1

Given, let the mass of $H$ be $w$

$$\begin{array}{cccc}& mass& mole& molerratio\\ C& 6w& \frac{6w}{12}& 0.5=3\\ H& w& \frac{w}{1}& 1=6\\ N& \frac{7w}{1.5}& \frac{7w}{1.5\times 14}& \frac{1}{3}=2\end{array}$$
So, the empirical formula = $C_3{H}_6{N}_2$
Hence empirical formula mass = 70
Least possible molar mass = 140

Hence $\frac{\text{least possible molar mass}}{28}=\frac{140}{28}=5$