IB Chemistry SL 1.4.6 Avogadro's Law

Practise using equal gas volumes at the same temperature and pressure as direct measures of mole ratio. Read coefficients from a balanced gas equation to identify the limiting…

Exam points

translate balanced-equation coefficients directly into gas-volume ratios at fixed conditions
identify the limiting gas from the available volumes before calculating product volume
subtract the reacting volume to determine how much excess gas remains after completion

[Maximum number: 1]

Two hydrides of nitrogen are ammonia and hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4}$ . One derivative of ammonia is methanamine whose molecular structure is shown below.

Figure for Question 1.4.6—Avogadro's law question 1 — IB Chemistry SL

Calculate, showing your working, the mass of hydrazine needed to remove all the dissolved oxygen from $1000 \mathrm{dm}^{3}$ of the sample.

Calculate the volume, in $\mathrm{dm}^{3}$ , of nitrogen formed under SATP conditions.
(The volume of 1 mol of gas $=24.8 \mathrm{dm}^{3}$ at SATP.)

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$<\mathrm{n}\left(\mathrm{~N}_{2} \mathrm{H}_{4}\right)=\mathrm{n}\left(\mathrm{O}_{2}\right)=\frac{8.0 \mathrm{~g}}{32.00 \mathrm{~g} \mathrm{~mol}^{-1}}=>0.25<\mathrm{mol}>$

«volume of nitrogen $=0.25 \mathrm{~mol} \times 24.8 \mathrm{dm}^{3} \mathrm{~mol}^{-1} »=6.2$ « $\mathrm{dm}^{3}$ »

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1.4.6—Avogadro's law question 1