sblock Elements 1 Question 15
11. The correct statements among (a) to (d) regarding $\mathrm{H}_{2}$ as a fuel are :
(2019 Main, 11 Jan I)
I. It produces less pollutants than petrol.
II. A cylinder of compressed dihydrogen weights $\sim 30$ times more than a petrol tank producing the same amount of energy.
III. Dihydrogen is stored in tanks of metal alloys like $\mathrm{NaNi}_{5}$.
IV. On combustion, values of energy released per gram of liquid dihydrogen and LPG are 50 and $142 \mathrm{~kJ}$, respectively.
(a) I, II and III only
(b) II, III and IV only
(c) II and IV only
(d) I and III only
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Solution:
- (I) $\mathrm{H}_{2}$ is a $100 %$ pollution free fuel. So, statement (I) is correct.
(II) Molecular weight of $\mathrm{H}_{2}(2 \mathrm{u})$.
$=\frac{1}{29} \times$ molecular weight of butane,
$\mathrm{C}{4} \mathrm{H}{10}$ (LPG) [58u].
So, compressed $\mathrm{H}_{2}$ weighs $\sim 30$ times more than a petrol tank and statement (II) is correct.
(III) $\mathrm{NaNi}{5}, \mathrm{Ti}-\mathrm{TiH}{2}$ etc. are used for storage of $\mathrm{H}_{2}$ in small quantities. Thus, statement (III) is correct.
(IV) On combustion values of energy released per gram of liquid dihydrogen $\left(\mathrm{H}_{2}\right): 142 \mathrm{~kJ} \mathrm{~g}^{-1}$, and for LPG : $50 \mathrm{~kJ} \mathrm{~g}^{-1}$. So, staement (IV) is incorrect.
