One volume of hydrogen combines with sulphur to produce one volume of gas (A). If the vapour density of (A) be 17, what is its molecular formula ? Volumes have been measured under similar conditions of temperature and pressure.

Explanation

According to the available information :
`{:("Hydrogen + S",rarr,"Gas (A)"),("1 vol",,"1 vol"),("n molecules",,"n molecules"),("1 molecule",,"1 molecule"),("2 atoms",,"1 molecule"):}`
Let 2 atoms of hydrogen combine with x atoms of the element sulphur. Therefore, the molecular formula of the gas (A) will be `H_(2)S_(x)`
Molar mass of the gas `= 2 xx V.D = 2 xx 17 = 34` (given)
By comparison , `2 xx 1 + x xx 32 = 34 or x=1`
`:.` Molecular formula of gas (A) `= H_(2)S`.