Electron Transfer Reactions (SL IB Chemistry)

In winemaking, to prevent the oxidation of ethanol by air, sulfur dioxide (SO₂) is added. In order to calculate the amount of SO_2, a sample is titrated with iodine (I₂). The reaction is a one to one ratio for SO₂ and I₂ to produce H₂SO₄ as well as another product. 

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

20 cm³ of a 0.60 mol dm^–3 solution of thallium nitrate (TlNO₃) requires 40 cm³ of
0.20 mol dm^–3 acidified ammonium metavanadate (NH₄VO₃) to produce Tl³⁺_(aq) ions. 

Vanadium is the only element reduced in this reaction. What is the oxidation number of the reduced vanadium?

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 are correct?

1. Chlorine is reduced in reaction 2
2. Bromine is reduced in both reaction 1 and reaction 2
3. Bromine is oxidised in both reaction 1 and reaction 2

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 statements correctly describe the process? 

1. The H⁺(aq) ion is oxidised by NO₂^–(aq).
2. Some nitrogen atoms are oxidised, and some nitrogen atoms are reduced.
3. The H⁺(aq) ion acts as a catalyst.

A voltaic cell consisting of zinc and silver is set up. The following overall reaction takes place:

                            Zn(s)   +  2Ag⁺(aq)  →  Zn²⁺(aq)  +  2Ag(s)                    

What are the correct half-equations at each electrode? 

Which statement about the movements of electrons in voltaic cells is correct?

When molten magnesium chloride is electrolysed using graphite electrodes what are the products? 

Use the information given about four reactions of metals to determine the order of reactivity from most reactive to least reactive

   W(s) + X²⁺(aq) → W²⁺(aq) + X(s)

   Y(s) + W²⁺(aq) → No Reaction

   X(s) + Y²⁺(aq) → X²⁺(aq) + Y(s)

   Z(s) + Y²⁺(aq) → No Reaction

Which statements about voltaic cells are correct? 

1. 1.    A redox reaction takes place which produces electrical energy.
   2.    At the cathode, an oxidation reaction occurs.
   3.    Electrons move from the anode to the cathode.

An organic compound Y with molecular formula C₅H₁₂O, is oxidised to compound Z with molecular formula C₅H₁₀O₂.

What could be the structural formula of Y?

1. CH₃(CH₂)₄OH
2. CH₃CH₂CH(CH₂OH)CH₃
3. CH₃C(CH₃)₂CH₂OH

A number of alcohols with the formula C₄H₁₀O are separately oxidised. Using 7.41 g of the alcohols a 50% yield of organic product is achieved.

What mass of product could be obtained?

1. 4.41 g of butanoic acid.
2. 4.41 g of 2-methylpropanoic acid.
3. 3.61 g of butanone.

Which alcohol could not be produced by the reduction of an aldehyde or a ketone?

Which molecule(s) can be both reduced by sodium borohydride, NaBH_4, and oxidised by warm acidified potassium dichromate (VI)? 

1. CH₃CHBr(CH₃)₂CCHO
2. CH₃CHOHCH₂CH₃
3. (CH₃)₃CCHO

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

Which of the following statements is correct?

Four reactions are shown below. In which reaction is the species shown 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 takes 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 oxidizing agent?

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? 

What is formed at the electrodes during the electrolysis of molten potassium iodide? 

Below is a diagram of a voltaic cell. When the cell is running, what is happening in the salt bridge?

2.30 g of ethanol were mixed with aqueous acidified potassium dichromate(VI) and the desired organic product was collected by immediate distillation under gentle warming. The yield of the product was 50.0%. ( RAMs C= 12, H=1, O=16)

What mass of product was collected?

Which alcohol gives only one possible oxidation product when warmed with dilute acidified potassium dichromate(VI)?

Hydroxyethanal has the structural formula HOCH₂CHO.

In an experiment hydroxyethanal is heated under reflux with an excess of acidified potassium dichromate(VI) until no further oxidation takes place.

What is the skeletal formula of the organic product formed in the experiment?

Use the following electrode potentials to answer the question.

Sn²⁺ (aq) + 2e^- ⇌ Sn (s)      E^θ = -0.14 V

Fe³⁺ (aq) + e^- ⇌  Fe²⁺ (aq)  E^θ = +0.77 V

What will be the EMF, in V, when the following voltaic cell is connected?

Sn (s) + 2Fe³⁺ (aq) → 2Fe²⁺ (aq) + Sn²⁺ (aq)