Home / AS & A Level Chemistry 2.4 Reacting masses and volumes Exam Style Practice Questions Paper 1
Methanethiol, \(\mathrm{CH_3SH}\), burns as shown.
\(\mathrm{CH_3SH+3O_2\rightarrow CO_2+SO_2+2H_2O}\)
A sample of \(10\,\mathrm{cm^3}\) of methanethiol gas was reacted with \(60\,\mathrm{cm^3}\) of oxygen. Both samples were measured at room conditions.
What would be the final volume of the resultant mixture of gases measured at room temperature?
Correct Answer: \( \boxed{\mathrm{C}} \)
Gas volumes are proportional to the number of moles.
\(10\,\mathrm{cm^3}\) of \(\mathrm{CH_3SH}\) requires:
\(\mathrm{3\times10=30\,cm^3}\) of \(\mathrm{O_2}\).
Oxygen remaining:
\(\mathrm{60-30=30\,cm^3}\)
Products formed:
Final gas volume:
\(\mathrm{30+10+10=50\,cm^3}\)
Therefore, the correct answer is (C).
Methane and steam react to produce hydrogen.
\( \mathrm{CH_4(g)+2H_2O(g)\rightarrow CO_2(g)+4H_2(g)} \)
\(0.80\,\mathrm{g}\) of methane and \(1.35\,\mathrm{g}\) of steam react. One of the reactants is used up.
Which volume of hydrogen, measured at room conditions, will be produced?
Correct Answer: \( \boxed{\mathrm{B}} \)
Moles of methane:
\(n=\dfrac{0.80}{16}=0.050\,\mathrm{mol}\)
Moles of steam:
\(n=\dfrac{1.35}{18}=0.075\,\mathrm{mol}\)
The reaction requires \(2\,\mathrm{mol}\) of steam for every \(1\,\mathrm{mol}\) of methane.
For \(0.050\,\mathrm{mol}\) methane, \(0.100\,\mathrm{mol}\) steam is needed, but only \(0.075\,\mathrm{mol}\) is available.
Therefore, steam is the limiting reagent.
From the equation,
\(2\,\mathrm{mol}\ \mathrm{H_2O}\rightarrow4\,\mathrm{mol}\ \mathrm{H_2}\)
Hydrogen produced \(=0.075\times2=0.150\,\mathrm{mol}\).
At room conditions, \(1\,\mathrm{mol}=24\,\mathrm{dm^3}\).
Volume of hydrogen \(=0.150\times24=3.60\,\mathrm{dm^3}\).
Therefore, the correct answer is (B).
A washing powder contains sodium hydrogencarbonate, \( \mathrm{NaHCO_3} \), as one of the ingredients.
In a titration, a solution containing \(1.00\,\mathrm{g}\) of this washing powder requires \(7.15\,\mathrm{cm^3}\) of \(0.100\,\mathrm{mol\,dm^{-3}}\) sulfuric acid for complete reaction. The sodium hydrogencarbonate is the only ingredient that reacts with the acid.
What is the percentage by mass of sodium hydrogencarbonate in the washing powder?
Correct Answer: \( \boxed{\mathrm{C}} \)
The balanced equation is:
\( \mathrm{H_2SO_4 + 2NaHCO_3 \rightarrow Na_2SO_4 + 2CO_2 + 2H_2O} \)
Moles of \( \mathrm{H_2SO_4} \):
\(0.100 \times \dfrac{7.15}{1000}=7.15\times10^{-4}\,\mathrm{mol}\)
From the equation:
Moles of \( \mathrm{NaHCO_3}=2\times7.15\times10^{-4}=1.43\times10^{-3}\,\mathrm{mol}\)
Mass of \( \mathrm{NaHCO_3} \):
\(1.43\times10^{-3}\times84.0=0.120\,\mathrm{g}\)
Percentage by mass:
\( \dfrac{0.120}{1.00}\times100=12.0\% \)
Therefore, the correct answer is (C).