Electrochemistry (CIE A Level Chemistry)

Oxidation numbers can be used to balance equations. Chlorine and hot aqueous sodium hydroxide react to produce chloride ions, chlorate 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)

The chemistry of the Group VII elements often involves redox processes. 

Which statement is correct?

Four reactions are shown. In which reaction is the species in bold acting as an oxidising agent?

In which compound are there two different elements with the same oxidation number?

When sulfuric acid and sodium iodide react one of the reactions that take place is shown by the equation below

8NaI + 9H₂SO₄ → 8NaHSO₄ + 4I₂ + H₂S + 4H₂O

Which species has been oxidised in this reaction?

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

3TiO₂ + 4BrF₃ → 3TiF₄ + 2Br₂ + 3O₂

Which element increases in oxidation number in this reaction?

In which reaction does hydrogen behave as an oxidising agent?

Chlorine gas reacts with both hot and cold aqueous sodium hydroxide, each resulting in a different set of products.

What are the oxidation numbers of chlorine in the products of these reactions?

When solid potassium halides are added to concentrated sulfuric acid, the following reactions take place:

In each reaction, what is the largest change in the oxidation number of sulfur?

When heated ammonium nitrate, NH₄NO₃, can decompose explosively.

NH₄NO₃ → N₂O + 2H₂O

The nitrogen atoms in NH₄NO₃ have different oxidation numbers.

What are the changes in the oxidation numbers when this reaction proceeds?

The acid HIO disproportionate 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 → r I₂ + s HIO₃ + t H₂O

The equation can be balanced using oxidation numbers.

What are the values for r and s?

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). The reaction is a one to one ratio for SO₂ and I₂.

What is the change in the oxidation number of sulfur in this reaction?

The table shows the redox potentials of a number of species.

Half reaction	/  V
V3+ (aq) + e-  V2+ (aq)	- 0.26
VO2+ (aq) + 2H+ (aq) + e-  V3+ (aq) + H2O (l)	+ 0.34
S4O62- (aq) + 2e-  2S2O32- (aq)	+ 0.47
2VO2+ (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 thiosulphate ions?

The oxidation state of chlorine can range from –1 to +7 in its compounds.

Which reagent(s) and conditions are necessary to oxidise elemental chlorine into a compound containing chlorine in the +5 oxidation state?

A student set up experiments to observe the outcome of adding different sodium halides to concentrated phosphoric acid and concentrated sulfuric acid. She recorded her findings in the table below.

Which deduction can be made from these observations?

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 statements about these reactions are correct?

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?

Which pair of reactants will result in a redox reaction?

How does concentrated sulfuric acid behave when it reacts with sodium chloride?