Question

510mg of a liquid on vaporization in victor Mayor’s apparatus displaces 67.2 ml of dry air (at NTP). The molecular weight of liquid is:
A.130
B.17
C.1700
D.170

Answer 1

Hint: Mayor’s apparatus is the laboratory method which is a standard method for determining the molecular weight of a volatile liquid. Volatile solid contains a mass or liquid under examination which is converted into vapor from heating in the mayor's tube. The vapor displaces its own volume of air. Here temperature and pressure are calculated.

Complete step by step answer:
The mass of organic compounds, volume of air displaced, room temperature, atmospheric pressure and aqueous tension are the states which are used in the formula to find the molecular weight.
Then, using the values and forms $\dfrac{{{P_1}{V_1}}}{{{T_1}}} = \dfrac{{{P_2}{V_2}}}{{{T_2}}}$
Volume of the dry air at NTP, ${V_2} = \dfrac{{{P_1}{V_1}}}{{{T_1}}} \times \dfrac{{{T_2}}}{{{P_2}}} = \dfrac{{{P_1}{V_1}}}{{{T_1}}} \times \dfrac{{273}}{{760}} = V$ ml
V ml of vapor weigh=W g
22400 ml of vapor weigh $ = \dfrac{W}{V} \times 22400g$
Now, we add the given values,
510 mg compounds mean $510 \times {10^{ - 3}}$ gm compounds since 1 mg contain ${10^{ - 3}}$ gm.
Mol. Wt. of compound $ = \dfrac{{510 \times {{10}^{ - 3}}}}{{67.2}} \times 22400$
= 170.0
Here we find the molecular weight of liquid by Mayor’s apparatus is 170.

Hence option (D) is the correct answer.

Note: Mayor’s apparatus is the standard method. Here we remember that determining the molecular weight of a volatile liquid. Here mass of the solid or liquid is determined in this method. The vapor displaces its volume and calculates the mass by the using value of 22400. A small quantity of glass-wool or asbestos pad covers the lower end of the Victor Meyer’s tube and is sealed immediately.