`116 mg` of a compound on vaporisation in a Victor `-` Meyer's apparatus displaced `44.8 mL` of air measured at `S.T.P.` The molecular mass of the compound is

Options

A. `116 u`
B. `232 u`
C. `58 u`
D. `45 u`

Answer

C

Explanation

Victor Meyer's method is a convenient method for the determination of molecular masses of volatile substances. A known mass of a substance is converted into vapor. The vapor is made to displace an equal volume of air which can be collected over water.
Volume of air displaced at `STP`
`=` Volume of vapor at o .c. at `STP`
`= 44.8 mL`
Thus, `44.8mL` of vapors of organic compound at `STP` weigh `116 mg`.
`22, 400mL` of vapors of organic compound at `STP` will weigh
`(116 mg)/(44.8 mL) xx 22, 400 mL = 58000 mg = 58 g`
Since `1 mol` of the vapor at `STP` always occupies`22,400 mL` and has mass equal to molar mass, the molecular mass of the compound is `58 u`.