Lesson 15B.1

15B.1 Vanadium and dichromate redox chemistry Quiz: Pearson Edexcel Chemistry, Unit 15

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 15B.1, Vanadium and dichromate redox chemistry: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 15: Transition Metals, written with Revision Ninja.

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The 20 questions

  1. What colour is the vanadium(V) ion, V(+5), in its compounds?

    • Yellow
    • Green
    • Blue
    • Violet

  2. What colour is vanadium(IV) in its compounds?

    • Green
    • Violet
    • Yellow
    • Blue

  3. Which reagent reduces vanadium(V) stepwise to vanadium(II) in acid?

    • Chlorine water
    • Zinc in acid
    • Hydrogen peroxide in alkali
    • Aqueous silver nitrate

  4. What colour is the chromate(VI) ion, CrO4 2-?

    • Green
    • Yellow
    • Orange
    • Pink

  5. What colour is the dichromate(VI) ion, Cr2O7 2-?

    • Yellow
    • Green
    • Blue
    • Orange

  6. What happens to chromate ions when acid is added?

    • They are converted to dichromate ions, and the solution turns green
    • They are converted to dichromate ions, and the solution turns orange
    • They are reduced to Cr metal
    • They are converted to Cr3+ ions without any colour change

  7. What is the oxidation number of vanadium in the VO2+ ion?

    • +4
    • +3
    • +2
    • +5

  8. What is the oxidation number of chromium in both CrO4 2- and Cr2O7 2-?

    • +6 and +7
    • +3 and +6
    • +6 in both
    • +4 and +6

  9. Which statement about acidic conditions and the chromate-dichromate equilibrium is correct?

    • pH has no effect on the equilibrium
    • Basic conditions favour dichromate, the orange ion
    • Acidic conditions favour chromate, the yellow ion
    • Acidic conditions favour dichromate, the orange ion

  10. Can zinc metal reduce Cr3+ to Cr2+ under standard conditions? (E-zero Zn2+/Zn = -0.76 V, Cr3+/Cr2+ = -0.41 V)

    • No, because E-zero cell = -1.17 V, which shows that Cr2+ would be oxidised by zinc metal instead
    • No, because E-zero cell = -0.35 V, so zinc cannot reduce Cr3+ to Cr2+ under standard conditions
    • Yes, because E-zero cell = -0.41 - (-0.76) = +0.35 V, which is positive
    • Yes, because E-zero cell = +1.17 V, which would make the reduction very fast under standard conditions

  11. Why is alkaline hydrogen peroxide used to oxidise Cr3+ to chromate(VI)?

    • Alkaline H2O2 reduces Cr to Cr2+
    • Acid is needed to reduce Cr3+ to chromium metal
    • Hydroxide reduces dichromate back to Cr3+
    • Alkaline conditions allow Cr3+ to be oxidised to chromate

  12. What is the oxidation state of vanadium in V2O5?

    • +4
    • +5
    • +3
    • +2

  13. Why is Cr2+ a strong reducing agent?

    • Cr2+ has no d electrons, so it cannot be oxidised
    • Its Cr3+/Cr2+ E-zero is positive, so Cr2+ is a strong oxidant
    • Its Cr3+/Cr2+ E-zero is negative (-0.41 V), so Cr2+ is readily oxidised
    • Cr2+ is inert to all oxidants in aqueous solution

  14. Which statement about dichromate in acid is correct? (E-zero Cr2O7 2-/Cr3+ = +1.33 V)

    • Dichromate in acid is a strong reducing agent
    • Dichromate is inert in acid and does not oxidise anything
    • Dichromate has E-zero -1.33 V
    • Dichromate in acid is a strong oxidising agent

  15. In the reaction of dichromate with Fe2+ in acid, how many moles of Fe2+ react with 1 mol of Cr2O7 2-?

    • 1
    • 6
    • 3
    • 2

  16. How many moles of Fe2+ react with 25.0 cm3 of 0.0200 mol dm-3 K2Cr2O7?

    • 1.00 x 10^-3 mol
    • 1.20 x 10^-2 mol
    • 3.00 x 10^-3 mol
    • 5.00 x 10^-4 mol

  17. Why does zinc reduce vanadium(V) stepwise rather than all at once?

    • Each reduction step is a separate electron transfer with its own E-zero
    • Vanadium cannot be reduced by any metal in acid
    • Zinc always reduces all oxidation states in a single step
    • Stepwise reduction happens only in alkaline solution

  18. Why does adding H+ to a yellow chromate solution make it orange?

    • Adding H+ shifts the equilibrium to the right, forming more Cr2O7 2-
    • Adding H+ shifts the equilibrium to the left, forming more CrO4 2-
    • H+ is a spectator, so the colour cannot change
    • Adding OH- is what converts chromate to dichromate

  19. Why does the reduction of dichromate by zinc in acid show several colour changes?

    • Chromium stays in one oxidation state but changes its ligands, which changes the colour each time
    • Zinc changes its own colour in the reaction as it dissolves to form zinc ions in the solution
    • Chromium passes through several oxidation states, Cr(VI), Cr(III) and Cr(II), each with a different colour
    • Colour changes come only from the acid, not from chromium, which is colourless in all its states

  20. A solution of V2+ is left exposed to air. What is the expected outcome?

    • It stays violet indefinitely with no change, because air cannot react with any vanadium species
    • It is oxidised all the way to V5+ at once, turning yellow in a single step without intermediates
    • It is reduced by air to vanadium metal, which precipitates out of the solution as a dark solid
    • It is oxidised by air to V3+, changing colour from violet to green

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