International ASChemistryEdexcelExam Questions2. Energetics, Group Chemistry, Halogenoalkanes and Alcohols2.3 Redox Chemistry & Acid-Base Titrations

Redox Chemistry & Acid-Base Titrations (Edexcel International AS Chemistry)

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2.3 Redox Chemistry & Acid-Base Titrations

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2.3 Redox Chemistry & Acid-Base Titrations

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1
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What is the oxidation number of chromium in Na2Cr2O7?

  • +1

  • +2   

  • +3

  • +6

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2
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In an oxide of nitrogen, the oxidation number of nitrogen is +4.

Which is the formula of the oxide?

  • N2O

  • N2O3

  • N2O4

  • N2O5

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3
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What is the oxidation number of phosphorus in the phosphate ion, Pstraight O subscript 4 superscript 3 minus end superscript?

  • –3

  • +3

  • +5

  • +7

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11 mark

Hydrogen peroxide, H2O2, breaks down into water and oxygen.

In terms of oxidation and reduction, how do hydrogen and oxygen change in this reaction?

      Hydrogen Oxygen
  ☐ A oxidised reduced
  ☐ B oxidised and reduced unchanged
  ☐ C reduced oxidised
  ☐ D unchanged oxidised and reduced

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    21 mark

    Iodate(V) ions, Ibegin mathsize 16px style O subscript 3 to the power of minus sign end style, oxidise dithionate ions, S2straight O subscript 6 superscript 2 minus end superscript, according to the equation

    x Ibegin mathsize 16px style O subscript 3 to the power of minus sign end style+ y S2straight O subscript 6 superscript 2 minus end superscript+ 4H2O → z Sbegin mathsize 16px style O subscript 4 to the power of 2 minus sign end style+ 8H++ I2

    What are the balancing numbers x, y and z?

          x y z
      ☐ A 2 1 2
      ☐ B 2 2 4
      ☐ C 2 5 5
      ☐ D 2 5 10

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      31 mark

      Magnesium reacts with hydrochloric acid.

      Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

      Which statement about this reaction is correct?

      • magnesium atoms act as oxidising agents

      • hydrogen molecules act as reducing agents

      • hydrogen ions act as oxidising agents

      • chloride ions act as oxidising agents

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      4
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      The formulae of four ions are shown.

      Formula of ion
      CrO42-
      AlO2-
      [Fe(CN)6]4-
      [CrCl2(H2O)4]+

      How many of these ions contain a metal with an oxidation number of +3?

      • one

      • two

      • three

      • four

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      5a1 mark

      This question is about the reaction shown.

      2KMnO4 + xH2C2O4 + yH2SO4 → 2MnSO4 + K2SO4 + 10CO2 + zH2O

      a)
       What values of x, y and z are needed to balance the equation?

            x y z
        ☐ A 5 6 8
        ☐ B 10 3 4
        ☐ C 5 3 8
        ☐ D 10 6 4

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        5b
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        b)
        What is the reducing agent in the reaction?

        • H+

        • C2O42-

        • MnO4

        • SO4

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        6
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        Which name is correct for the ion Sstraight O subscript 4 superscript 2 minus end superscript ?

        • sulfate(II)

        • sulfate(IV)

        • sulfate(VI)

        • sulfate(VIII)

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        7
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        A diprotic acid, H2A, was titrated with sodium hydroxide solution.

        H2A (aq) + 2NaOH (aq) rightwards arrow Na2A (aq) + 2H2O (l)

        A 25.0 cm3 portion of 0.100 mol dm−3 sodium hydroxide solution required 12.80 cm3 of the solution of the diprotic acid for complete neutralisation.
        What is the concentration of H2A in mol dm−3?

        • 2.56 × 10−2

        • 9.77 × 10−2

        • 1.95 × 10−1

        • 3.91 × 10−1

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        8
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        In which compound is the oxidation number of nitrogen +5?

        • Ca(NO3)2

        • Mg3N2

        • N2O3

        • NaNO2

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        91 mark

        Which reaction is not a redox reaction?

        • 4KClO3 (s) → 3KClO4 (s) + KCl (s)

        • 2HCl (aq) + Ba(OH)2 (aq) → BaCl2 (aq) + 2H2O (l)

        • Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)

        • Cl2 (g) + H2O (l) → HCl (aq) + HClO (aq)

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        101 mark

        In which reaction is the copper species acting as an oxidising agent?

        •  Cu2+ + 2Ag → 2Ag+ + Cu

        • 2Cu++ O2– → Cu2O

        • 3Cu + O2 → Cu2O + CuO

        • Cu + Hg2+ → Hg + Cu2+

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        11
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        Two half‐equations for a reaction are shown.

        Cu → Cu2+ + 2e−

        NO3− + 4H+ + 3e− → NO + 2H2O

        What is the overall ionic equation for this reaction?

        • Cu + Nstraight O subscript 3 superscript minus+ 4H+→ Cu2+ + NO + 2H2O

        • 2Cu + Nbegin mathsize 16px style O subscript 3 to the power of minus sign end style+ 4H+→ 2Cu2+ + NO + 2H2O

        • 3Cu + 2Nstraight O subscript 3 superscript minus+ 8H+→ 3Cu2+ + 2NO + 4H2O

        • 6Cu + 2Nstraight O subscript 3 superscript minus+ 8H+→ 6Cu2+ + 2NO + 4H2O

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        12
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        A titre of 13.25 cm3 was obtained using a 50 cm3 burette.

        What is the percentage uncertainty in the titre?

        [Each reading of the burette has an uncertainty of ±0.05 cm3]

        • ±0.38%

        • ±0.75%

        • ±1.5%

        • ±7.5%

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        13a
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        a)

        A pellet of sodium hydroxide has a mass of 0.700 g.

        Some pellets were dissolved to make 350 cm3 of 0.25 mol dm–3 solution.

        [Mr value: NaOH = 40]

        How many pellets were dissolved?

        • 4

        • 5

        • 8

        • 125

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        13b
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        b)

        25.0 cm3 of the sodium hydroxide solution prepared in (a) was placed in a conical flask and titrated with sulfuric acid.

        2NaOH + H2SO4 → Na2SO4 + 2H2O

        Calculate the number of moles of sulfuric acid that reacted.

        • 0.0031

        • 0.0063

        • 0.013

        • 0.044

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        13c1 mark
        c)
        Phenolphthalein indicator was used for the titration in (b). 
        What was the colour change at the endpoint?

        • colourless → pink

        • pink → colourless

        • orange → yellow

        • yellow → orange

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        1a
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        A group of students carry out an experiment to find the concentration of chlorine, Cl2 (aq), in a solution.

        Excess potassium iodide solution is added to a 10.0 cm3 sample of the chlorine solution.

        Cl2 (aq) + 2I− (aq) rightwards arrow 2Cl− (aq) + I2 (aq)

        The iodine produced is titrated with a solution of thiosulfate ions of known concentration, using starch indicator.

        2S2O32- (aq) + I2 (aq) → S4O62- (aq) + 2I− (aq)

        The concentration of the Cl2 (aq) is between 0.038 and 0.042 mol dm−3 .

        What concentration of thiosulfate ions, in mol dm−3 , is required to give a titre of approximately 20 cm3 ?

        • 0.010

        • 0.020

        • 0.040

        • 0.080

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        1b
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        What is the most suitable volume of 0.1 mol dm−3 potassium iodide solution, in cm3, to add to the 10.0 cm3 of chlorine solution?

        • 7.6

        • 8.0

        • 8.4

        • 10.0

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        1c
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        What is the colour change at the end‐point of the titration?

        • colourless to pale yellow

        • pale yellow to colourless

        • colourless to blue‐black

        • blue‐black to colourless

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