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A welding fuel gas contains carbon and h...

A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide, 0.690 g of water and no other products. A volume of 10.0 litre (Measured at STP) of this welding gas is found weigh `11.6 g`. Calculate
(i) empirical formula,
(ii) molar mass of the gas, and
(iii) molecular formula.

Text Solution

Verified by Experts

`underset(44 g)(CO_(2)) =underset(12 g) ( C)`
Mass of carbon `=12/14 xx 44 xx 3.38 =0.92`g
`underset(18g)(H_(2)O) =underset(2 g)(H_(2))`
Mass of hydrogen `=2/18 xx 0.690 = 0.077`
Percentage of C `=(0.922)/(0.922 + 0.077) xx 100 = 92.2%`
Percentage of H `=(0.077)/(0.922 + 0.077) xx 100 = 7.7%`
(i) Calculation of empirical formula:

Empirical formula = CH
(ii) Calculation of molar mass
10.0 L of gas at S.T.P. weigh = 11.6 g
22.4 g of gas at S.T.P. weigh `=(11.6)/(10.0) xx 22.4`
`=26 g "mol"^(-1)`
(iii) Calculation fo molecular formula:
Empirical formula mass = 12 + 1=13
Molecular mass = 26
`n=("Molecular mass")/("Empirical formula mass")`
`=26/13=2`
`therefore` Molecular formula =2(CH)
`=C_(2)H_(2)`.
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