TOPIC

Oxidotion ond Reduction

E Multiple Choice Quesfions

In which of the following will a redox reaction occur?

A. addition of aqueous ammonium chloride to aqueous silver nitrate

B. addition of aqueous sodium carbonate to dilute hydrochloric acid

C. addition of aqueous ammonia to aqueous zinc sulfate

D. addition of magnesium to iron (III) nitrate

) Gas X causes aqueous potassium iodide to change from colourless to brown. Gas Y produces dense white

fumes when mixed with ammonia. Which of the following elements is present in both X and Y?

A. carbon

B. nitrogen

C. chlorine

D. bromine

3. Chlorine reacts with cold aqueous sodium hydroxide according to the following equation:

Clr(g) + 2NaOH(aq) -+NaC/O(aq) + NaC/(aq) + HrO(l)

Which of the following statements is correct?

A. Chlorine is reduced and sodium hydroxide is oxidised.

B. Chlorine is oxidised and sodium hydroxide is reduced.

C. Chlorine is both oxidised and reduced.

D. Sodium hydroxide is both oxidised and reduced.

4. The manufacture of nitric acid from ammonia can be represented by the following equation:

NH, -+ NO -+ NO, + HNO,

Which of the following shows the change in the oxidation states of nitrogen at each stage of the

process?

A. +4-+ +2-+ +4 -+ +5

B. +5 -+ +2-+ +4 -+ +6

C. +3 -+ +2 -+ +4 -+ +5

D. -3 -+ +2 -+ +4 -+ +5

In which of the following reactions does the oxidation state of nitrogen show the greatest increase?

A. NH,(g) + HC/(g) -+ NHoC/(s)

B. 2NH,(g) + 3CuO(s) -+ Nr(g) + 3Cu(s) + 3HrO(l)

C. 4NO,(g) + Olg) + 2HrO(l) -+ 4HNO.(I)

D. 2NO,-(aq) + Cu(s) + 4H.(aq) -+ 2NOr(g) + Cu2*(aq) + 2HrO(l)

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6. Which of the following are redox reactions?

I MgO +2HCl -+MgC/r+HrOII Mg+2HCl-+MgC/r+H,III MnO, + 4HCl -+ MnC/, + 2HrO + Cl,

A. I and II onlyB. I and III onlyC. II and III onlyD. All of the above

7.

8.

dry ammonia ---->

Acidified potassium dichromate (VI) can be used to detect the presence of ethanol vapour in a person's

breath. A colour change from orange to green is observed if there is ethanol. This shows that ethanol is

A. a catalyst.

B. an alkali.

C. an oxidising agent.

D. a reducing agent.

Which of the following underlined substances has been reduced?

A. N2 to NH3

B. NH, to NO

C. NH, to NOfD. NO2 to NO3-

9. In which of the following reactions is the underlined substance reduced?

A. Cl, + -21: -+ 2Cl + I,B. Zn + HrSOo -+ ZnSOo + H,C. Fe2* + Hro, -+ Fe3*+ H2o

D. CUO + H, -+ Cu + HrO

10. Dry ammonia gas was passed over heated copper (II) oxide.

copper (II) oxide

----> nitrogen andwater vapour

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Which of the following statements is correct?

A. Ammonia is the reducing agent.

B. The oxidation state ofhydrogen decreased from +l to 0.

C. The oxidation state of nitrogen decreased from +3 to 0.

D. Copper (II) oxide remains unchanged at the end of the reaction.

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11. The major oxidation states of manganese (Mn) are +2, +4 and +7.

Which of the following contains millganese in all three oxidation states?

A. KMnOo, MnC/, MnO,

B. Mn(SOr)r, NaMnOo, Mn(NO,)z

C. MnBr, MnO, NaMnOo

D. MnO, KMnOo, Mn(SOr).,

12. Which statement is true about oxidising agents?

A. Their oxidation state is zero.

B. They are easily oxidised.

C. They never contain hydrogen.

D. They readily accept electrons.

13. 2KI(aq) + HrSrOr(aq) -+ Ir(s) + KrSOo(aq) + HrSOo(aq)

In the reaction above, H2S2O8 is behaving as

A. an acid.

B. an oxidising agent.

C. a reducing agent.

D. a base.

14. How can an oxidising agent be identified?

A. It tums acidified potassium dichromate (VI) green.

B. It tums potassium manganate (VII) colourless.

C. It turns Universal Indicator red.

D. It tums aqueous potassium iodide brown.

15. The oxidation states of chlorine in C/Oo- and C/rO respectively are

A. -l and -1B. +3 and +lC. +7 and +1

D. +'l and +2

16. Which of the following is not a redox reaction?

A. Fer(SOo), + HrS -+ 2FeSOo + H2SO4

B. 2Al + 6HCl -+ 2AlCl.+3H,C. CaCO, + CO, + HrO -+ Ca(HCO,),

D. 2KClOi + zKCl +2O2

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1.

E Stn chrred Queslions

Copper reacts with heated concentrated nitric acid to yield a brown acidic gas NOr, copper (II) nitrate and

water.

(a) Write a balanced chemical equation, with state symbols, for the reaction.(b) What is the colour of the solution in the beaker?

(c) Complete the table below.

copper

nltrogen

(d) Explain, in terms of oxidation states, whether the reaction is a redox reaction.

(a) When silver bromide is exposed to sunlight, silver ions are reduced to silver atoms. This reaction

is the basis of photography.

(i) Explain why this reaction is an example of reduction.(ii) Write an ionic equation for this reaction.

(b) Hydrogen chloride can be manufactured by reacting hydrogen and chlorine.(i) Write a balanced chemical equation for the reaction.

(ii) Discuss whether the reaction is a redox reaction.

(a) Deuterium (symbol D) is the name given to the isotope of hydrogen that contains one proton and

one neutron in the nucleus. The compound DrO is called 'heavy water'.(i) Calculate the relative molecular mass of DrO. Why is the name 'heavy water' appropriate for

this molecule?(ii) Draw a diagram showing all the electrons, protons and neutrons in a molecule of 'heavy

water'.(iii) 'Heavy water'has the same reactions as normal water, but its reactions are usually slower.

Explain this difference in reaction rates.

(b) By writing the equation, or by naming the reagents, show how you would carry out each of the

conversions shown below.

DrO -+ D, -+ DC/ -+ A/C/,

(c) What is the oxidation state of deuterium in DrO, D, and DC/ respectively?

(a) Define oxidation both in terms of electron transfer and hydrogen atoms.(b) Name a substance which is an oxidising agent in aqueous solution. Explain how aqueous potassium

iodide can be used to confirm that this named substance is an oxidising agent.

Potassium dichromate (VI) solution acidified with dilute sulfuric acid is a common laboratory reagent.

On reacting, dichromate (VI) ions change to chromium (III) ions.(a) State the colour change when acidified potassium dichromate (VI) reacts.

(b) (i) Write the formulae of dichromate (VI) ions and chromium (III) ions.(ii) What is the oxidation number of chromium in each of these two ions?

(c) (i) By referring to oxidation numbers, explain whether the dichromate (VI) ions are oxidised orreduced.

(ii) Is acidified potassium dichromate an oxidising agent or a reducing agent?

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3.

4.

Element Initial oxidation state Final oxidation state

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6. Study the chemical reactions below. A chemistry student thinks that they are all redox reactions. Do you

agree? Circle T or F accordingly.

(a) 2CrHo(g) + 7Or(g) -+ 4COr(g) + 6HrO(g) T/F

(b) NarCO.(s) + 2HCl(aq) + 2NaC/(aq) + HrO(l) + COr(g) T/F

(c) 2KI(aq) + Pb(NOr)r(aq) -+ Pblr(s) + 2KNO.,(aq) T/F

(d) 2Na(s) + 2HrO(l) + 2NaOH(aq) + Hr(g) TIF

(e) FerO,(s) + 3CO(g) -+ 2Fe(l) + 3COr(g) TIF

(f) Zn(s) + 2AgNO.(aq) -+ Zn(NOr)r(aq) + 2Ag(s) TIF

(g) NaOH(aq) + HNO,(aq) -+NaNO,(aq) + HrO(l) TIF

(h) H.(aq) + OH (aq) -+HrO(l) T/F

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