Question

Calculate the molar mass of the following substances.
(a) Ethyne, `C_(2)H_(2)`
(b) Sulphur molecule, `S_(8)`
(c) Phosphorus molecule, `P_(4)` (Atomic mass of phosphorus = 31)
(d) Hydrochloric acid, HCl
(e) Nitric acid, `HNO_(3)`

Answer 1

The molar masses of all these substances will be equal to the respective molecular masses expressed in `g//"mol"`. Now :
(a) Molar mass of ethyne, `C_(2)H_(2) = "Mass of " C xx 2 + "Mass of" H xx 2`
`= 12 xx 2 +1 xx 2`
`= 24 + 2`
`= 26 g //"mol"`
(b) Molar mass of sulphur molecule, `S_(8) = "Mass of S" xx 8` ltbRgt `= 32 xx 8`
`= 256 g//"mol"`
(c ) Molar mass of phosphorus molecule. `P_(4) = "Mass of P" xx 4`
`= 31 xx 4`
`= 124 g //"mol"`
(d) Molar mass of hydrochloric acid, HCl `= "Mass of H" xx Mass of Cl"`
`= 1+ 35.5` ltrgt `= 36.5 g//"mol"`
(e ) Mass of nitric acid, `HNO_(3) = "Mass of H" + "Mass of N" + "Mass of O" xx 3`
`= 1 +14 + 16 xx 3`
`= 15 + 48`
`= 63 g//"mol"`