Question

a fuel gas 'x' combustion gives 2.2 kg co2 and 1.8 kg h2o only write the

1) emppirial formula

2) molecular mass

3) its 2 uses as fuel

Answer 1

Given that fuel gas on combustion gives carbon dioxide and water.Let the fuel gas is X.
X (s) + O₂(g) $\to$CO₂​ (g) + H₂O (l)
2.2 kg 1.8 kg


Molar mass of CO₂ = 12 + 2$\times$16= 44 g
Amount of carbon in 44 g CO₂ = 12 g
​Amount of carbon in 2.2 kg CO₂ = $\frac{12}{44}\times 2.2\times 1000$ g​ =600 g

Molar mass of H₂O = 1$\times$2 + 16= 18 g
Amount of hydrogen in 18 g H₂O​ = 2 g
​Amount of hydrogen in 1.8 kg H₂O​ = $\frac{2}{18}\times 1.8\times 1000$ g​ =200 g

Since it is given that it is a fuel gas it would consist of carbon and hydrogen only.
Thus total amount of fuel gas used for combustion = 600 g + 200 g = 800 g

Percentage of carbon in fuel gas = $\frac{600}{800}\times 100$ = 75 %

Percentage of hydrogen in compound = $\frac{200}{800}\times 100$ = 25 %​

Element	Atomic mass of element	Percentage	Moles of the constituents	Molar ratio	Simple whole number ratio
C	12	75	$\frac{75}{12}=6.25$	$\frac{6.25}{6.25}=1$	1
H	1	25	$\frac{25}{1}=25$	$\frac{25}{6.25}=4$	4

Thus the simple ratio of C:H is 1:4

Thus empirical formula of the compound = CH₄

​Molecular mass = $12+1\times 4=16\mathrm{amu}$

This fuel gas is methane.
Uses of methane as fuel :
1) Methane in form of natural gas is used for running scooters , cars , buses etc.
2) Liquid methane is also used as rocket fuel.