Exam code: 9701
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Redox Processes: Electron Transfer & Changes in Oxidation Number (Oxidation State)
Which row correctly describes oxidation and reduction in terms of the transfer of electrons and changes in oxidation number?
Transfer of electrons | Change in oxidation number | |||
|---|---|---|---|---|
Oxidation | Reduction | Oxidation | Reduction | |
A | Gain | Loss | Increase | Decrease |
B | Loss | Gain | Increase | Decrease |
C | Loss | Gain | Decrease | Increase |
D | Gain | Loss | Decrease | Increase |
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The heptahydrate mineral of magnesium sulfate is used in Epsom salts for preparing therapeutic baths.
What is the sum of all the oxidation numbers in MgSO4?
-2
+2
+7
0
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Which row gives the most common oxidation numbers of fluorine, oxygen and hydrogen in compounds?
F | O | H | |
|---|---|---|---|
A | +7 | −1 | −1 |
B | +1 | +2 | +1 |
C | −1 | −1 | −1 |
D | −1 | −2 | +1 |
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Solutions containing chlorate ions decompose on heating as shown:
3ClO- (aq) → ClO3- (aq) + 2Cl- (aq)
Which row is correct for the oxidation number of the chlorine in each ion?
ClO- | ClO3- | Cl- | |
|---|---|---|---|
A | +1 | +5 | −1 |
B | +1 | +3 | −1 |
C | −1 | +5 | −1 |
D | −1 | +3 | −1 |
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A student added a solution of iodine to a solution of sodium bromide. Which statement correctly describes what happens?
No reaction occurs.
The bromide ions are oxidised.
The iodine molecules are oxidised.
Both the bromide ions and iodine molecules undergo changes in their oxidation state.
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In which of the following reactions is the change in oxidation number the smallest for nitrogen?
N2H4 (g) + 3O2 (g) → 2NO2 (g) + 2H2O (g)
3Mg (s) + N2 (g) → Mg3N2 (s)
4NH3 (g) + 5O2 (g) → 4NO (g) + 6H2O (g)
2NO (g) + O2 (g) → 2NO2 (g)
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In the compound [ICl2]+[SbCl6]−, the oxidation number of chlorine is −1.
Which row gives 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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Titanium dioxide is obtained from the ore ilmenite, FeTiO3, in which iron has an oxidation number of +2.
FeTiO3 (s) → TiO2 (s)
What is the change in the oxidation number of titanium in the reaction?
+4 to +5
+3 to +4
No change
+6 to +4
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In which of the following compounds is the oxidation number of nitrogen the highest?
N2O
NO
NaNO2
N2O4
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In which reaction does an element have the largest change in oxidation number?
Cr2O72- (aq) + 6Fe2+ (aq) + 14H+ (aq) → 2Cr3+ (aq) + 6Fe3+ (aq) + 7H2O (l)
3ClO- (aq) → ClO3- (aq) + 2Cl- (aq)
5Fe2+ (aq) + MnO4- (aq) + 8H+ (aq) → 5Fe3+ (aq) + Mn2+ (aq) + 4H2O (l)
PbO2 (s) + Sn2+ (aq) + 4H+ (aq) → Sn4+ (aq) + Pb2+ (aq) + 2H2O (l)
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Sulfur dioxide and oxygen difluoride react together.
SO2 (g) + OF2 (g) → SO3 (g) + F2 (g)
Which row is correct?
sulfur | fluorine | oxygen in OF2 | |
|---|---|---|---|
A | Oxidised | Reduced | Reduced |
B | Reduced | Oxidised | Reduced |
C | Oxidised | Oxidised | Reduced |
D | Reduced | Oxidised | Oxidised |
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Chlorine and hot aqueous sodium hydroxide react to produce chloride ions, chlorate(V) ions and water.
What are the values of the coefficients p, r and s in the equation?
pCl2 (g) + qOH− (aq) → rCl− (aq) + sClO3− (aq) + tH2O (l)
p | r | s | |
|---|---|---|---|
A | 3 | 5 | 1 |
B | 3 | 4 | 2 |
C | 2 | 3 | 1 |
D | 4 | 6 | 2 |
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Which statement about the redox chemistry of the halogens is correct?
Bromine can oxidise chloride ions.
Iodide ions are the weakest reducing agents of the first four Group 17 ions.
In reactions with water, chlorine is oxidised and reduced.
Fluorine is a weaker oxidising agent than chlorine.
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In which reaction is the species in bold acting as an oxidising agent?
Cr2O72- (aq) + 8H+ (aq) + 3SO32- (aq) → 2Cr3+ (aq) + 4H2O (l) + 3SO42- (aq)
Mg (s) + Fe2+ (aq) → Mg2+ (aq) + Fe (s)
Cl2 (aq) + 2Br- (aq) → 2Cl- (aq) + Br2 (aq)
Fe2O3 (s) + 3CO (g) → 2Fe (s) + 3CO2 (g)
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In which compound do two different elements have the same oxidation number?
Mg(OH)2
Na2SO4
HClO
NH4Cl
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When solid sodium iodide and concentrated sulfuric acid react, one of the reactions that takes place is shown below.
8NaI (s) + 9H2SO4 (l) → 8NaHSO4 (s) + 4I2 (g) + H2S (g) + 4H2O (l)
Which species is oxidised in this reaction?
I-
SO42-
Na+
H+
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The following reaction can be used to determine the mass of titanium dioxide in an ore.
3TiO2 (s) + 4BrF3 (l) → 3TiF4 (s) + 2Br2 (l) + 3O2 (g)
Which element increases in oxidation number in this reaction?
Bromine
Fluorine
Oxygen
Titanium
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In which reaction does hydrogen act as an oxidising agent?
2Na (s) + H2 (g) → 2NaH (s)
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
H2 (g) + Cl2 (g) → 2HCl (g)
C2H4 (g) + H2 (g) → C2H6 (g)
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Chlorine gas reacts with both hot and cold aqueous sodium hydroxide, each resulting in a different set of products.
Which row gives the oxidation numbers of chlorine in the products of these reactions?
Hot aqueous sodium hydroxide | Cold aqueous sodium hydroxide | |
|---|---|---|
A | −1 and +5 | −1 and +1 |
B | −1 and +5 | −1 and +2 |
C | +1 and +6 | −1 and +1 |
D | +1 and +6 | −1 and +2 |
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When solid potassium halides are added to concentrated sulfuric acid, the following reactions take place:
Reaction 1 | 2KBr (s) + 2H2SO4 (l) → K2SO4 (s) + SO2 (g) + Br2 (l) + 2H2O (l) |
|---|---|
Reaction 2 | 8KI (s) + 5H2SO4 (l) → 4K2SO4 (s) + H2S (g) + 4I2 (s) + 4H2O (l) |
Reaction 3 | 2KCl (s) + H2SO4 (l) → K2SO4 (s) + 2HCl (g) |
In each reaction, what is the greatest change in the oxidation number of sulfur?
Reaction 1 | Reaction 2 | Reaction 3 | |
|---|---|---|---|
A | 1 | 4 | 1 |
B | 2 | 4 | 0 |
C | 2 | 8 | 0 |
D | 4 | 8 | 1 |
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The table shows various ions containing manganese and chlorine. In which row are the oxidation numbers of the central atoms identical?
manganese-containing ion | chlorine-containing ion | oxidation number of central atom | |
|---|---|---|---|
A | MnO4- | ClO3- | +7 |
B | MnO42- | ClO2- | +6 |
C | MnO4- | ClO3- | +5 |
D | MnO4- | ClO4- | +7 |
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When heated, ammonium nitrate, NH4NO3, can decompose explosively.
NH4NO3 (s) → N2O (g) + 2H2O (g)
The nitrogen atoms in NH4NO3 have different oxidation numbers.
What are the changes in the oxidation numbers when this reaction proceeds?
+4 and −4
−2 and −4
+4 and −6
+2 and +6
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The acid HIO disproportionates when in aqueous solution. This is shown in the equation, where q, r, s and t are simple whole numbers in their lowest ratios.
q HIO (aq) → r I2 (aq) + s HIO3 (aq) + t H2O (l)
What are the values for r and s?
r | s | |
|---|---|---|
A | 4 | 2 |
B | 4 | 1 |
C | 2 | 1 |
D | 1 | 2 |
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In winemaking, to prevent oxidation of ethanol by air, sulfur dioxide (SO2) is added. In order to calculate the amount of SO2, a sample is titrated with iodine (I2).
What is the change in the oxidation number of sulfur in this reaction?
+2 to +6
+4 to +6
+2 to +4
+4 to +5
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The table shows the standard electrode potentials of a number of species.
half-equation | E° / V |
|---|---|
V3+ (aq) + e− ⇌ V2+ (aq) | −0.26 |
VO2+ (aq) + 2H+ (aq) + e− ⇌ V3+ (aq) + H2O (l) | +0.34 |
S4O62− (aq) + 2e− ⇌ 2S2O32− (aq) | +0.09 |
VO2+ (aq) + 2H+ (aq) + e− ⇌ VO2+ (aq) + H2O (l) | +1.00 |
What is the lowest possible oxidation number that vanadium(V) can be reduced to by thiosulfate ions?
+2
+3
+4
+5
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The oxidation number of chlorine can range from −1 to +7 in its compounds.
Which reagents and conditions allow elemental chlorine to produce a compound containing chlorine in the +5 oxidation state?
Concentrated H2SO4 at room temperature.
AgNO3 (aq) followed by NH3 (aq) at room temperature.
Cold dilute NaOH (aq).
Hot concentrated NaOH (aq).
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Solid sodium chloride and solid sodium iodide were each added separately to concentrated phosphoric acid and concentrated sulfuric acid. The results are shown in the table below.
sodium chloride | sodium iodide | |
|---|---|---|
concentrated H3PO4 | colourless acidic gas formed | colourless acidic gas formed |
concentrated H2SO4 | colourless acidic gas formed | purple vapour formed |
Which deduction can be made from these observations?
Concentrated sulfuric acid is a stronger oxidising agent than chlorine.
Concentrated sulfuric acid is a stronger oxidising agent than iodine.
Concentrated phosphoric acid is a stronger oxidising agent than iodine.
Concentrated phosphoric acid is a stronger oxidising agent than concentrated sulfuric acid.
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If a solution contains both bromine and chlorine, BrO3– ions are produced.
The reactions leading to the production of BrO3– ions are shown below:
Reaction 1: Br2 + H2O → HBr + HBrO
Reaction 2: 3HBrO + Cl2 → 2Cl– + BrO3– + Br2 + 3H+
Which statement about these reactions is correct?
In reaction 1, bromine is reduced only.
In reaction 2, chlorine is oxidised.
In reaction 2, bromine is oxidised only.
In both reactions, bromine undergoes disproportionation.
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A dilute acid is added to an aqueous solution containing nitrite ions, NO2–, and two different nitrogen compounds are released as gases.
2H+ (aq) + 2NO2– (aq) → H2O (l) + NO (g) + NO2 (g)
Which statement about this reaction is correct?
The H+ ion is oxidised in this reaction.
Nitrogen is only reduced in this reaction.
The H+ ion acts as a catalyst in this reaction.
Some nitrogen atoms are oxidised and some are reduced in this reaction.
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The following reactions are carried out:
Reaction 1: CH3COCH3 + Tollens' reagent
Reaction 2: CH3CH2CHO + Fehling's reagent
Reaction 3: C2H4 + Br2
Which statement about these reactions is correct?
Propanone undergoes oxidation when it reacts with Tollens' reagent.
Fehling's solution is reduced when it reacts with propanal.
Bromine is oxidised when it reacts with ethene.
Only reaction 2 involves a change in oxidation number.
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How does concentrated sulfuric acid behave when it reacts with solid sodium chloride?
as a reducing agent only
as an oxidising agent only
as an acid only
as an acid and an oxidising agent
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