OCR AS Chemistry

Topic Questions

2.3 Acid-base & Redox Reactions

11 mark

Which equation is not a neutralisation reaction?

  • Ca (s) + 2HCl (aq) → CaCl2 (aq) + H2 (g)

  • H+ (aq) + OH (aq) → H2O (l)

  • K2CO3 (s) + 2HNO3 (aq) → 2KNO3 (aq) + H2O (l) + CO2 (g)

  • NH3 (aq) + HCl (aq) → NH4Cl (aq)

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2
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1 mark

What is the oxidation number of nitrogen in Mg(NO3)2?

  • -3

  • +2

  • +5

  • +6

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31 mark

Which equation represents a redox reaction?

  • Mg + 2HCl rightwards arrow MgCl2 + H2

  • MgO + 2HCl rightwards arrow H2O + MgCl2

  • MgCO3+ 2HCl rightwards arrow CO2 + H2O + MgCl2

  • Mg(OH)2 + 2HCl rightwards arrow MgCl2 +2H2O

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41 mark

Which reaction shows oxidation of sulfur?

  • 2HBr + H2SO4 → SO2 + 2H2O + Br2

  • SO2 + 2NaOH → Na2SO3 + H2O

  • 8HI + H2SO4 → 4I2 + H2S + 4H2O

  • H2S + Cl2 → 2HCl + S

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51 mark

What is the oxidation number of Mn in K2MnO4?

  • +4

  • +5

  • +6

  • +7

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61 mark

Which are the correct common oxidation states of fluorine, oxygen and hydrogen in compounds?

  Fluorine Oxygen Hydrogen
A -1 -2 +1
B -7 -1 -1
C +1 +2 +1
D +7 -1 -1

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71 mark

The heptahydrate mineral of magnesium sulfate is used in Epsom Salts for preparing therapeutic baths. Magnesium sulfate is also used in some medical applications.

What is the overall oxidation state of MgSO4?

  • -2

  • +2

  • +7

  • 0

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81 mark

Europium metal reacts with sulfuric acid to form europium(III) sulfate and hydrogen gas.

What is the formula of europium(III) sulfate?

  • EuSO4

  • Eu(SO4)2

  • Eu2(SO4)3

  • Eu3(SO4)2

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91 mark

A reaction occurs between aqueous calcium hydroxide and nitric acid.

Which is the correct ionic equation for the reaction?

  • Ca(OH)2 + 2HNO3 → Ca(NO3)2 + H2O

  • H+ + OH- →  H2O

  • Ca2+ + 2NO3- → Ca(NO3)2 

  • CaOH + HNO3 → CaNO3 + H2O

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1
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1 mark

Which reagent would exactly neutralise 100 cm3 of 1.00 mol dm–3 H2SO4 (aq)?

  • 0.100 mol Al(OH)3

  • 0.100 mol NH3

  • 0.100 mol Ba(OH)2

  • 0.100 mol NaOH

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2
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1 mark

In the compound [ICl2]+ [SbCl]6- the oxidation number of chlorine is –1.

What are the oxidation numbers of I and Sb in the compound?

  I Sb
A +1 +5
B +1 +7
C +3 +5
D +3 +7

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31 mark

A solution containing both bromine and chlorine will produce bromate ions, BrO3.

The reactions leading to the production of BrO3 ions are: 

Reaction 1: Br2  +  H2O  →  HBr  +  HBrO
Reaction 2: 3HBrO  +  Cl2  →  2Cl   +  BrO3  +  Br2  +  3H+

Which statements about these reactions are correct?

  Chlorine is reduced in reaction 2 Bromine is reduced in both reaction 1 and reaction 2 Bromine is oxidised in both reaction 1 and reaction 2
A X X
B X
C X
D

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41 mark

If a dilute acid is added to an aqueous solution containing nitrite ions, NO2, two different nitrogen compounds are released as gases.

2H+ (aq) + 2NO2 (aq) → H2O (l) + NO (g) + NO2 (g)

Which of the three statements below correctly describe the process?

  The H+ (aq) ion is oxidised by NO2- (aq) Some nitrogen atoms are oxidised, and some nitrogen atoms are reduced The H+ (aq) ion acts as a catalyst
A X
B X X
C X
D

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51 mark

What are the correct oxidation numbers for the elements in Fe3O4?

  Fe O
A +3 and +4 -1
B +2.67 -2
C +2 and +3 -2
D +4 -3

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6
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1 mark

A student performed a titration. The burette readings from one titration are shown below.

Final reading / cm3 28.65
Initial reading / cm3 7.25

The burette the student used has an uncertainty of ±0.05 cm3.

What is the percentage uncertainty of the resulting titre?

  • 0.17%

  • 0.23%

  • 0.35%

  • 0.47%

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7
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1 mark

A student titrated 25.0 cm3 of 0.30 mol dm-3 of aqueous potassium hydroxide, KOH (aq),  with 0.10 mol dm-3 of aqueous phosphoric(V) acid, H3PO4 (aq). The equation for the reaction is shown below.

H3PO4 (aq) + 3KOH (aq) → K3PO4 (aq) + 3H2O (l)

Which statement is correct?

  • If the concentration of H3PO4 (aq) is doubled, the volume of KOH (aq) required to reach the end point will be halved.

  • The end point is reached when 25.0 cm3 of H3PO4 (aq) has been added.

  • Once the titration is complete, 0.00750 mol of H2O is present.

  • The end point is reached when 75.0 cm3 of H3PO4 (aq) has been added.

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8
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1 mark

A solution of an unknown carbonate, X2CO3, was prepared by dissolving 3.63 g in 250 cm3 of distilled water in a volumetric flask.

25.0 cm3 of the solution was titrated with 0.20 mol dm-3 hydrochloric acid. The mean titre of hydrochloric acid required to reach the end point was 26.20 cm3.

Which is the correct identity of X?

  • Sodium

  • Magnesium

  • Potassium

  • Calcium

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9
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1 mark

30.0 cm3 of a 0.10 mol dm-3 solution of an unknown acid, HxA, reacted completely with 45 cm3 of a 0.200 mol dm-3 solution of lithium hydroxide.

Which is the correct equation for the reaction?

  • HA + LiOH → LiA + H2O

  • H2A + 2LiOH → Li2A + 2H2O

  • H3A + 3LiOH → Li3A + 3H2O

  • H2A + Li(OH)2 → LiA + 2H2O

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10
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1 mark

Which one of the following is the electron arrangement of the element that is reduced most easily?

  • 1s2 2s2 2p4

  • 1s2 2s2 2p6 3s2 3p3

  • 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

  • 1s2 2s2 2p6 3s2 3p6

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11 mark

Titanium dioxide can be obtained from the ore ilmenite, Fe(II)TiO3

FeTiO3 → TiO2

What is the change in the oxidation number of titanium in the reaction?

  • +3 to +4

  • +4 to +5

  • +6 to +4

  • No change in oxidation number occurs 

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21 mark

What is the oxidation number of Cr in Cr(H2O)63+?

  • 0

  • +1

  • +2

  • +3

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3
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1 mark

25.0 cm3 of hydrochloric acid solutions reacts with 36.2 cm3 of 0.225 mol dm-3 sodium hydroxide solution. 

What is the concentration of the acid?

  • 0.326 mol dm-3

  • 8.15 x 10-3 mol dm-3

  • 1.55 x 10-4  mol dm-3

  • 0.65 mol dm-3

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4
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1 mark

When a sample of sodium hydroxide, NaOH, is dissolved in 250 cm3 of distilled water. 25.0 cm3 of this solution is titrated against sulfuric acid with a concentration of 2.00 mol dm-3. Complete neutralisation takes place with 15.0 cm3 of sulfuric acid.

2NaOH + H2SO4 → Na2SO4 + 2H2O

What is the mass of the original sample of sodium hydroxide dissolved in 250 cm3 of distilled water? 

  • 1.20 g

  • 12.0 g

  • 2.40 g

  • 24.0 g

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51 mark

Which of the following represents a redox reaction?

  • Fe + 2HCl → FeCl2 + H2

  • 2NH+ HNO3 → NH4NO3

  • K2CO3 + 2CH3COOH → 2CH3COOK + CO2 + H2

  • ZnO + H2SO4 → ZnSO4 + H2

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61 mark

In which reaction does hydrogen behave as an oxidising agent?

  • H2 + CuO → Cu + H2O

  • 2Na + H2 → 2NaH

  • H2 + Cl2 → 2HCl

  • C2H4 + H2 → C2H6

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71 mark

Which reaction shows the species in bold acting as an oxidising agent?

  • 2MnO4- + 5SO32- + 6H+ → 2Mn2+ + 3H2O + 5SO42-

  • Fe2O3 + 3CO → 2Fe + 3CO2

  • Mg + Fe2+ → Mg2+ + Fe

  • Cl2 + 2Br- → 2Cl- + Br2

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81 mark

The following reaction can be used to determine the mass of titanium dioxide in an ore.

3TiO2 + 4BrF3 → 3TiF4 + 2Br2 + 3O2

Which element decreases in oxidation state in this reaction?

  • Oxygen 

  • Fluorine 

  • Bromine 

  • Titanium 

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9
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1 mark

A student titrate as a solution of strontium hydroxide, Sr(OH)2 (aq), with hydrochloric acid, HCl (aq). 25.00 cm3 of 0.055 mol dm-3 Sr(OH)2 was needed to neutralise 24.80 cm3 of HCl (aq).

What is the concentration of the acid?

  • 0.03 mol dm-3

  • 1.38 x 10-3 mol dm-3

  • 0.11 mol dm-3

  • 0.06 mol dm-3

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101 mark

What is the oxidation state of Cl in Cl2O7?

  • +14

  • +5

  • +7

  • 0

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