Redox Chemistry

Ilmenite is a mineral made mainly of a mixture of iron(II) titanate, FeTiO₃, and iron(III) titanate, Fe₂(TiO₃)₃. Which row shows the oxidation state of titanium in the two compounds?

The table shows the formulae of compounds formed by carbon and other elements.

In which two substances does carbon have the same oxidation state?

The compound Bi₂Sr₂Ca₂Cu₃O₁₀ is a superconductor. In it, bismuth is +3, strontium and calcium are +2 and oxygen is −2. What are the possible oxidation numbers of the three copper atoms?

During the Contact process, sulfuric acid is produced from sulfur in a series of stages: S → SO₂ → SO₃ → H₂S₂O₇ → H₂SO₄. Which statement correctly describes these stages?

Concentrated sulfuric acid reacts with solid potassium halides:

reaction 1: H₂SO₄ + 2KCl → 2HCl + K₂SO₄
reaction 2: 2H₂SO₄ + 2KBr → 2H₂O + Br₂ + K₂SO₄ + SO₂
reaction 3: 5H₂SO₄ + 8KI → 4H₂O + 4I₂ + 4K₂SO₄ + H₂S

What is the change in the oxidation state of the sulfur that reacts in each reaction?

Nitrogen monoxide is removed from car exhaust in a catalytic converter: 2CO + 2NO → N₂ + 2CO₂. Which statement about the reaction is not correct?

Sulfur dioxide is converted to sulfur trioxide in two stages.

stage 1: 2NO + O₂ → 2NO₂
stage 2: NO₂ + SO₂ → SO₃ + NO

Which statement is correct?

The results of some experiments with sulfur dioxide are shown.

Which experiments show correct results?

Aqueous iron(III) chloride reacts with aqueous potassium iodide: vFeCl₃ + wKI → xFeCl₂ + yKCl + I₂. Which statements are correct?

1 In the balanced equation, v, w, x and y have the same value.
2 A purplish-black vapour is produced in the reaction.
3 Potassium iodide is used to test for the presence of an oxidising agent.

NF₃ can be made from ammonia and fluorine: 4NH₃ + 3F₂ → NF₃ + 3NH₄F. Which statements about the reaction are correct?

1 NH₃ undergoes disproportionation.
2 The oxidation number of nitrogen in NF₃ is +3.
3 NH₃ is a stronger oxidising agent than F₂.
4 One mole of F₂ gains two moles of electrons.

50.0 cm³ of 0.100 mol dm⁻³ KClO₄(aq) reacted exactly with 50.0 cm³ of 0.400 mol dm⁻³ TiCl₃(aq). Ti(III) is oxidised to Ti(IV). What is the oxidation state of chlorine in the final product?

The most common oxidation state of americium, Am, in aqueous solution is +3. Cu³⁺ oxidises Am³⁺(aq) in dilute HNO₃ and is itself reduced to Cu²⁺. 20.0 cm³ of 0.0120 mol dm⁻³ Am³⁺(aq) required 24.00 cm³ of 0.0300 mol dm⁻³ Cu³⁺ for complete oxidation. What is the formula of the americium-containing species formed?

25.0 cm³ of a 0.100 mol dm⁻³ solution of M₂O₅ is reduced by sulfur dioxide to a lower oxidation state. 50.0 cm³ of 0.0200 mol dm⁻³ acidified potassium manganate(VII) is needed to re-oxidise M back to its original oxidation state. What is the oxidation state of M after reaction with sulfur dioxide?

0.84 g of an oxide MO of a metal M was dissolved in excess sulfuric acid. 25.0 cm³ of 0.12 mol dm⁻³ potassium manganate(VII) was required to oxidise M²⁺ to M³⁺. What is the relative atomic mass of M?

0.02 mol of an iodine oxide reacts with 0.2 mol of acidified potassium iodide to give 0.12 mol of iodine, I₂. What is the oxidation number of iodine in the oxide?

Consider the half-equations Fe²⁺ → Fe³⁺ + e⁻ and C₂O₄²⁻ → 2CO₂ + 2e⁻. 20 cm³ of an acidified 0.020 mol dm⁻³ solution of FeC₂O₄ is oxidised by 15 cm³ of 0.020 mol dm⁻³ KMnO₄. Both Fe²⁺ and C₂O₄²⁻ are oxidised. What is the final oxidation state of manganese?

A comproportionation reaction is one where two reactants, each containing the same element in a different oxidation state, form a product in which that element has one oxidation state. 2 mol of hydrogen sulfide, H₂S, react with 1 mol of another sulfur-containing compound to form 3 mol of sulfur, S. What is a possible identity of the sulfur-containing compound?

When potassium chlorate(V), KClO₃, is heated at its melting point, it disproportionates to potassium chlorate(VII), KClO₄, and potassium chloride. What is the maximum amount of potassium chlorate(VII) that could be produced from 0.200 mol of potassium chlorate(V)?

Excess iodide ions react with 15 cm³ of a solution containing copper(II) ions: 4I⁻ + 2Cu²⁺ → I₂ + 2CuI. The iodine formed requires 20 cm³ of 0.10 mol/dm³ sodium thiosulfate: I₂ + 2Na₂S₂O₃ → 2NaI + Na₂S₄O₆. What is the concentration of copper(II) ions in the solution?

The Winkler method finds the amount of dissolved oxygen in water.

step 1: 2Mn²⁺(aq) + O₂(g) + 4OH⁻(aq) → 2MnO(OH)₂(s)
step 2: MnO(OH)₂(s) + 2I⁻(aq) + 4H⁺(aq) → I₂(aq) + Mn²⁺(aq) + 3H₂O(l)
step 3: I₂(aq) + 2S₂O₃²⁻(aq) → 2I⁻(aq) + S₄O₆²⁻(aq)

A 5.00 dm³ sample of water needed a total of 4.00 × 10⁻³ mol of thiosulfate in step 3. What concentration of oxygen was present in the sample?

Excess chlorine was bubbled through 250 cm³ of aqueous sodium thiosulfate, Na₂S₂O₃, oxidising thiosulfate to sulfate ions. 25.0 cm³ of the resulting solution gave 0.583 g of barium sulfate precipitate with excess aqueous barium nitrate. What is the concentration, in mol dm⁻³, of sodium thiosulfate in the 250 cm³ of solution?

Iodate(V) ions react with iodide ions in acid: IO₃⁻ + 5I⁻ + 6H⁺ → 3I₂ + 3H₂O. 25.0 cm³ of sulfuric acid is added to a solution containing excess iodate(V) and iodide ions, and the iodine produced is titrated with sodium thiosulfate. 22.00 cm³ of 0.100 mol dm⁻³ sodium thiosulfate is needed. What is the concentration of the sulfuric acid, in mol dm⁻³?

Carbon monoxide in air reacts with iodine pentoxide: 5CO + I₂O₅ → I₂ + 5CO₂. The iodine is titrated with sodium thiosulfate: I₂ + 2S₂O₃²⁻ → S₄O₆²⁻ + 2I⁻. A 100 cm³ sample of polluted air gave iodine that needed 20.0 cm³ of 0.20 mol dm⁻³ sodium thiosulfate. What is the concentration, in g dm⁻³, of carbon monoxide in the sample?

Ethanedioate ions are oxidised by hot acidified potassium manganate(VII): 2MnO₄⁻ + 5C₂O₄²⁻ + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O. What volume of 0.020 mol dm⁻³ potassium manganate(VII) is needed to oxidise 1.0 × 10⁻³ mol of the salt KHC₂O₄·H₂C₂O₄?

25.0 cm³ of 0.01 mol dm⁻³ potassium manganate(VII) was added to 25.0 cm³ of 0.01 mol dm⁻³ ethanedioic acid. Z is the maximum volume of CO₂ produced at s.t.p. What is the value of Z?