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 14 of 16

1. Q104 · Original practice · 1 mark
   An indicator has equilibrium $\mathrm{HIn(aq)\rightleftharpoons H^+(aq)+In^-(aq)}$ and $pK_a=6.0$. HIn is yellow and In⁻ is blue. What is the expected dominant colour at pH 8.0?
   Acids, bases and titration
2. Q105 · Original practice · 1 mark
   A cell potential calculated from standard reduction potentials differs from the potential measured for the same pair of half-cells. Which observation best explains the difference?
   Redox and electrochemistry
3. Q106 · Original practice · 1 mark
   The table records whether a coating forms when each metal is placed in a solution of another metal’s ions. Which metal is the strongest reducing agent?
   Redox and electrochemistry
4. Q107 · Original practice · 1 mark
   The reduction potentials are $E^\circ(\mathrm{Al^{3+}/Al})=-1.66\ \mathrm V$ and $E^\circ(\mathrm{Ag^+/Ag})=+0.80\ \mathrm V$. What is the standard potential for $\mathrm{Al(s)+3Ag^+(aq)\to Al^{3+}(aq)+3Ag(s)}$?
   Redox and electrochemistry
5. Q108 · Original practice · 1 mark
   What is the correct name of $\mathrm{Fe_2(SO_4)_3}$?
   Redox and electrochemistry
6. Q109 · Original practice · 1 mark
   An organic compound has empirical formula $\mathrm{CH_2}$ and molar mass $84.0\ \mathrm{g\,mol^{-1}}$. Use C = 12.0 and H = 1.0. What is its molecular formula?
   Organic chemistry
7. Q110 · Original practice · 1 mark
   In $\mathrm{CH_3COCH_2CH_3}$, the class and the characteristic functional group are respectively
   Organic chemistry
8. Q111 · Original practice · 1 mark
   How is the haloalkane $\mathrm{CH_3CH_2CH(CH_3)CH_2Br}$ classified?
   Organic chemistry
9. Q112 · Original practice · 1 mark
   One mole of hex-2-yne undergoes complete hydrogenation to hexane. How many moles of hydrogen are consumed?
   Organic chemistry
10. Q113 · Original practice · 1 mark
    How many distinct non-cyclic alkane structural isomers have molecular formula $\mathrm{C_6H_{14}}$?
    Organic chemistry
11. Q114 · Original practice · 1 mark
    Which statement correctly describes a repeat unit of PTFE compared with a repeat unit of polyethene?
    Polymers and biomolecules
12. Q115 · Original practice · 1 mark
    Amino acid X migrates towards the negative electrode at pH 4.0 and towards the positive electrode at pH 8.0. Which isoelectric point is consistent with both observations?
    Organic analysis
13. Q116 · Original practice · 1 mark
    An amino-acid sample produces one spot on a TLC plate. Which conclusion is justified?
    Organic analysis
14. Q117 · Original practice · 1 mark
    In the contact process, sulfur trioxide is absorbed into concentrated sulfuric acid before water is added. Which equation represents the absorption step?
    Chemical synthesis
15. Q118 · Original practice · 1 mark
    An acidic hydrogen fuel cell consumes 0.0300 mol of oxygen. Assuming all of this oxygen forms water, how many moles of electrons pass through the external circuit?
    Chemical synthesis
16. Q119 · Original practice · 5 marks
    A flask contains liquid ethanol and ethanol vapour at equilibrium at constant temperature. Some liquid remains throughout the experiment. The stopper is then removed and vapour disperses into the surrounding air.
    Chemical equilibrium
17. Q120 · Original practice · 6 marks
    The graph shows concentrations for $\mathrm{A(g)\rightleftharpoons2B(g)}$. The temperature is constant. A single change is made at 4.0 min. The solid curve is A and the dashed curve is B. At the new equilibrium, $[A]=0.450\ \mathrm{mol\,L^{-1}}$ and $[B]=0.300\ \mathrm{mol\,L^{-1}}$.
    Chemical equilibrium
18. Q121 · Original practice · 5 marks
    A closed system is at equilibrium for $\mathrm{X(g)\rightleftharpoons Y(g)}$. A catalyst is added without changing temperature, volume or composition. The rates just before and just after addition are shown.
    Chemical equilibrium
19. Q122 · Original practice · 5 marks
    For $\mathrm{X(aq)\rightleftharpoons Y(aq)+Z(aq)}$, $K_c=3.0\times10^{-6}$ at a fixed temperature. Initially $[X]=0.300\ \mathrm{mol\,L^{-1}}$ and no Y or Z is present.
    Chemical equilibrium
20. Q123 · Original practice · 5 marks
    A student mixes 30.0 mL of $2.00\times10^{-3}\ \mathrm{mol\,L^{-1}}$ Pb(NO₃)₂ with 20.0 mL of $4.00\times10^{-3}\ \mathrm{mol\,L^{-1}}$ KI. Volumes are additive. At this temperature $K_{sp}(\mathrm{PbI_2})=8.0\times10^{-9}$.
    Chemical equilibrium
21. Q124 · Original practice · 4 marks
    Solid calcium carbonate and solid calcium oxide coexist with carbon dioxide at equilibrium: $\mathrm{CaCO_3(s)\rightleftharpoons CaO(s)+CO_2(g)}$. The vessel volume and temperature are constant.
    Chemical equilibrium
22. Q125 · Original practice · 5 marks
    A vessel initially contains $[H_2]=[I_2]=0.300$ and $[HI]=0.200\ \mathrm{mol\,L^{-1}}$. At its fixed temperature, $K_c=16.0$ for $\mathrm{H_2(g)+I_2(g)\rightleftharpoons2HI(g)}$.
    Chemical equilibrium
23. Q126 · Original practice · 5 marks
    A red solution contains the equilibrium $\mathrm{Fe^{3+}(aq)+SCN^-(aq)\rightleftharpoons FeSCN^{2+}(aq)}$. A small amount of Fe(NO₃)₃ is added. Its volume is negligible and the temperature is unchanged.
    Chemical equilibrium
24. Q127 · Original practice · 5 marks
    The table gives measured pH values for pure water at two temperatures. Use the self-ionisation equilibrium to analyse the observations.
    Acids, bases and titration