Chemistry questions and solutions

Browse original practice and official past-paper questions. Each question has its own link, with its source and worked solution.

364 questions · Page 11 of 16

1. Q32 · Original practice · 4 marks
   For $\mathrm{A(g)\rightleftharpoons B(g)}$, $K_c=3.0$ at a fixed temperature. Initially a 2.0 L vessel contains 0.80 mol A and no B.
   Chemical equilibrium
2. Q33 · Original practice · 4 marks
   A flask contains $\mathrm{H_2(g)+I_2(g)\rightleftharpoons2HI(g)}$. At equilibrium $[\mathrm{H_2}]=0.20$, $[\mathrm{I_2}]=0.30$ and $[\mathrm{HI}]=1.20\ \mathrm{mol\,L^{-1}}$.
   Chemical equilibrium
3. Q34 · Original practice · 4 marks
   $\mathrm{PCl_5(g)\rightleftharpoons PCl_3(g)+Cl_2(g)}$. Initially $[\mathrm{PCl_5}]=0.50\ \mathrm{mol\,L^{-1}}$ with no products. At equilibrium $[\mathrm{Cl_2}]=0.12\ \mathrm{mol\,L^{-1}}$.
   Chemical equilibrium
4. Q35 · Original practice · 4 marks
   The graph shows $\mathrm{A(g)\rightleftharpoons B(g)}$ in a constant-volume vessel. Only the temperature is increased at $t=4.0$ min. The solid line is B and the dashed line is A.
   Chemical equilibrium
5. Q36 · Original practice · 4 marks
   At $25^\circ\mathrm C$, the solubility product of $\mathrm{CaF_2}$ is $3.2\times10^{-11}$.
   Chemical equilibrium
6. Q37 · Original practice · 4 marks
   Equal volumes of $2.0\times10^{-4}\ \mathrm{mol\,L^{-1}}$ silver nitrate and $4.0\times10^{-4}\ \mathrm{mol\,L^{-1}}$ sodium chloride are mixed. For silver chloride, $K_{sp}=1.8\times10^{-10}$.
   Chemical equilibrium
7. Q38 · Original practice · 4 marks
   A saturated solution is in contact with excess $\mathrm{Mg(OH)_2(s)}$. Some sodium hydroxide is added, with negligible volume change.
   Chemical equilibrium
8. Q39 · Original practice · 4 marks
   A cleaning solution contains $4.0\times10^{-3}\ \mathrm{mol\,L^{-1}}$ sodium hydroxide at $25^\circ\mathrm C$.
   Acids, bases and titration
9. Q40 · Original practice · 4 marks
   A 0.080 mol L⁻¹ solution of a weak monoprotic acid has pH 3.00 at $25^\circ\mathrm C$.
   Acids, bases and titration
10. Q41 · Original practice · 5 marks
    Methanoic acid has $K_a=1.8\times10^{-4}$. A student prepares a 0.020 mol L⁻¹ solution.
    Acids, bases and titration
11. Q42 · Original practice · 5 marks
    A weak base B has $K_b=4.0\times10^{-5}$ at $25^\circ\mathrm C$.
    Acids, bases and titration
12. Q43 · Original practice · 4 marks
    An aqueous mixture contains appreciable ethanoic acid and sodium ethanoate.
    Acids, bases and titration
13. Q44 · Original practice · 6 marks
    The curve shows titration of 25.0 mL of a weak monoprotic acid with 0.100 mol L⁻¹ NaOH at $25^\circ\mathrm C$. The equivalence volume is 20.0 mL and the pH at half-equivalence is 5.00.
    Acids, bases and titration
14. Q45 · Original practice · 5 marks
    A solid sample of anhydrous sodium carbonate of mass 1.325 g is dissolved and made up to 250.0 mL. A 25.00 mL aliquot requires 24.60 mL HCl for complete neutralisation. Use $M(\mathrm{Na_2CO_3})=106.0\ \mathrm{g\,mol^{-1}}$.
    Acids, bases and titration
15. Q46 · Original practice · 5 marks
    A vinegar sample is diluted by transferring 10.00 mL to a 100.0 mL volumetric flask. A 20.00 mL aliquot of the dilution requires 16.40 mL of 0.1000 mol L⁻¹ NaOH. Treat all acidity as ethanoic acid; its molar mass is 60.05 g mol⁻¹.
    Acids, bases and titration
16. Q47 · Original practice · 5 marks
    The idealised conductometric curve shows 25.0 mL of hydrochloric acid titrated with 0.0500 mol L⁻¹ NaOH. Both branches intersect at 20.0 mL.
    Acids, bases and titration
17. Q48 · Original practice · 4 marks
    A student titrates a weak acid with strong base. Its steep pH change spans pH 7.5–10.5. Indicator X has $pK_a=4.0$ and indicator Y has $pK_a=9.0$.
    Acids, bases and titration
18. Q49 · Original practice · 5 marks
    In acidic solution, permanganate oxidises iron(II) to iron(III) and is reduced to manganese(II).
    Redox and electrochemistry
19. Q50 · Original practice · 5 marks
    Acidified dichromate reacts with iodide to form chromium(III) and iodine.
    Redox and electrochemistry
20. Q51 · Original practice · 5 marks
    A galvanic cell combines $\mathrm{Fe^{2+}/Fe}$ ($E^\circ=-0.44\ \mathrm V$) and $\mathrm{Ag^+/Ag}$ ($E^\circ=+0.80\ \mathrm V$) half-cells under standard conditions.
    Redox and electrochemistry
21. Q52 · Original practice · 4 marks
    The following standard reduction potentials are provided: $\mathrm{Mg^{2+}/Mg}=-2.37\ \mathrm V$, $\mathrm{Zn^{2+}/Zn}=-0.76\ \mathrm V$, $\mathrm{Cu^{2+}/Cu}=+0.34\ \mathrm V$.
    Redox and electrochemistry
22. Q53 · Original practice · 4 marks
    Aqueous copper(II) sulfate is electrolysed using graphite electrodes. Assume copper is deposited and oxygen evolves.
    Redox and electrochemistry
23. Q54 · Original practice · 4 marks
    Two aqueous sodium chloride solutions are electrolysed with inert electrodes. One is concentrated and one is very dilute. Use the syllabus model for preferential discharge.
    Redox and electrochemistry
24. Q55 · Original practice · 4 marks
    A jewellery workshop plates copper from $\mathrm{Cu^{2+}}$ solution using 0.800 A for 20.0 min. Assume 100% current efficiency. Use $F=96485\ \mathrm{C\,mol^{-1}}$ and $M(\mathrm{Cu})=63.55\ \mathrm{g\,mol^{-1}}$.
    Redox and electrochemistry