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 15 of 16

1. Q128 · Original practice · 6 marks
   The curve shows 25.0 mL of a weak monobasic base B titrated with 0.100 mol L⁻¹ HCl at 25 °C. The equivalence volume is 20.0 mL. At half-equivalence, pH = 9.20.
   Acids, bases and titration
2. Q129 · Original practice · 5 marks
   The idealised conductometric curve shows a weak monoprotic acid titrated with NaOH. It has been corrected for dilution. A 30.0 mL acid sample has equivalence volume 15.0 mL when the NaOH concentration is 0.0800 mol L⁻¹.
   Acids, bases and titration
3. Q130 · Original practice · 4 marks
   At 25 °C, 20.0 mL of 0.0600 mol L⁻¹ HCl is mixed with 15.0 mL of 0.0500 mol L⁻¹ Ba(OH)₂. Assume complete dissociation and additive volumes.
   Acids, bases and titration
4. Q131 · Original practice · 4 marks
   Solution X is 0.00500 mol L⁻¹ HCl with pH 2.30. Solution Y is 0.0500 mol L⁻¹ of a weak monoprotic acid with pH 3.30. Both are at the same temperature.
   Acids, bases and titration
5. Q132 · Original practice · 6 marks
   A 5.105 g sample of a pure monoprotic acid standard (molar mass 204.2 g mol⁻¹) is dissolved and made up to 250.0 mL. Separate 25.00 mL aliquots are titrated with NaOH. The titres are shown. A 25.00 mL aliquot of another monoprotic acid requires 18.80 mL of the same NaOH.
   Acids, bases and titration
6. Q133 · Original practice · 6 marks
   An unknown metal M forms M²⁺ ions. A galvanic cell uses M/M²⁺ and Cu/Cu²⁺ half-cells under standard conditions. Electrons flow from M to Cu and the cell potential is 1.10 V. Use the supplied reduction potentials.
   Redox and electrochemistry
7. Q134 · Original practice · 4 marks
   A steel object is connected separately to either magnesium metal or copper metal in an electrolyte. Use the reduction potentials Mg²⁺/Mg = −2.37 V, Fe²⁺/Fe = −0.44 V and Cu²⁺/Cu = +0.34 V. Treat the steel as iron and compare which metal is more readily oxidised.
   Redox and electrochemistry
8. Q135 · Original practice · 5 marks
   The diagram shows a standard hydrogen electrode connected to another half-cell. The electrode is platinum, the aqueous hydrogen-ion concentration is 1.0 mol L⁻¹, hydrogen pressure is 100 kPa and temperature is 25 °C.
   Redox and electrochemistry
9. Q136 · Original practice · 6 marks
   Hydrogen peroxide decomposes by $\mathrm{2H_2O_2(aq)\to2H_2O(l)+O_2(g)}$. This can be represented by one oxidation half-equation and one reduction half-equation in acidic solution.
   Redox and electrochemistry
10. Q137 · Original practice · 6 marks
    Two electrolytic cells are connected in series and therefore receive the same charge. Cell A deposits Ag from Ag⁺; cell B deposits Cu from Cu²⁺. A current of 0.500 A flows for 900 s. Cell A has 100% deposition efficiency. Cell B deposits 0.126 g Cu. Use F = 96485 C mol⁻¹, M(Ag) = 107.9 g mol⁻¹ and M(Cu) = 63.55 g mol⁻¹.
    Redox and electrochemistry
11. Q138 · Original practice · 5 marks
    Cell A contains molten sodium bromide. Cell B contains a very dilute aqueous sodium nitrate solution. Both use inert electrodes. For cell B, assume that water reacts at both electrodes and the nitrate ions do not react.
    Redox and electrochemistry
12. Q139 · Original practice · 5 marks
    A copper-plating cell uses an inert anode. The current is held constant during each interval in the table. Assume Cu²⁺ reduction at the cathode and oxygen formation from water at the anode, each with 100% current efficiency. Use F = 96485 C mol⁻¹, M(Cu) = 63.55 g mol⁻¹ and gas molar volume 24.8 L mol⁻¹.
    Redox and electrochemistry
13. Q140 · Original practice · 7 marks
    A nickel coating is required on 40.0 cm² of a metal object. Its uniform thickness must be 50.0 μm. Assume only Ni²⁺ reduction occurs at the object and current efficiency is 100%. Use density(Ni) = 8.90 g cm⁻³, M(Ni) = 58.69 g mol⁻¹ and F = 96485 C mol⁻¹. The current is 2.00 A. A pure nickel anode is used.
    Redox and electrochemistry
14. Q141 · Original practice · 5 marks
    Complete combustion of 0.460 g of a compound containing only C, H and O produces 0.880 g CO₂ and 0.540 g H₂O. Its molecular-ion mass is 46 for a singly charged ion. Use atomic masses C = 12.0, H = 1.0 and O = 16.0. The compound has a broad O–H absorption in its infrared spectrum.
    Organic chemistry
15. Q142 · Original practice · 5 marks
    Consider the non-cyclic, straight-chain alkenes with molecular formula $\mathrm{C_6H_{12}}$.
    Organic chemistry
16. Q143 · Original practice · 4 marks
    The neutral structural formula of alanine is shown. Its central carbon is attached to H, NH₂, CH₃ and COOH.
    Organic chemistry
17. Q144 · Original practice · 7 marks
    The pathway begins with 2-bromobutane. Under the specified conditions, route II gives but-2-ene as its major alkene product. Compounds X and Y are organic products.
    Organic chemistry
18. Q145 · Original practice · 5 marks
    A two-step synthesis converts ethane to ethylamine through chloroethane. Only the monosubstitution product is considered in the first step. Excess ammonia is used in the second step.
    Organic chemistry
19. Q146 · Original practice · 5 marks
    2-methylpropan-2-ol reacts with HBr to form a haloalkane and water. The haloalkane is then heated with ethanolic NaOH to form an alkene.
    Organic chemistry
20. Q147 · Original practice · 4 marks
    Ethanoic acid and methylamine undergo a condensation reaction under suitable heated, dehydrating conditions to form an amide. Treat the stated condensation as complete for the equation; do not model the initial acid–base salt.
    Organic chemistry
21. Q148 · Original practice · 5 marks
    A synthesis must produce 2.50 g of ethyl butanoate at an expected isolated yield of 75.0%. Butanoic acid and ethanol react in a 1:1 ratio. Ethanol is supplied in excess. Use M(butanoic acid) = 88.1 g mol⁻¹ and M(ethyl butanoate) = 116.2 g mol⁻¹.
    Chemical synthesis
22. Q149 · Original practice · 5 marks
    The diagram shows schematic methyl-group arrangements in three polypropene chains. Chain lengths and all other manufacturing conditions are the same.
    Polymers and biomolecules
23. Q150 · Original practice · 5 marks
    The repeat unit of PLA is shown. PLA and polypropene are both used in manufactured products.
    Polymers and biomolecules
24. Q151 · Original practice · 5 marks
    The diagrams show two cyclic forms of D-glucose. Both have formula C₆H₁₂O₆.
    Polymers and biomolecules