Redox Processes: Electron Transfer & Changes in Oxidation Number (Oxidation State) (CIE A Level Chemistry)

This question is about redox reactions.

When calcium reacts with Fe(NO₃)₂, a redox reaction occurs.

Ca + Fe(NO₃)₂ → Ca(NO₃)₂ + Fe

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What is the full systematic name for Fe(NO₃)₂?

Another redox reaction occurs between cobalt oxide, Co₂O₃, and hydrochloric acid, HCl.

Co₂O₃ + 6HCl → 2CoCl₂ + 3H₂O + Cl₂

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Magnesium oxide, MgO, reacts with nitric acid, HNO₃, when heated.

MgO + HNO₃ → Mg(NO₃)₂ + H₂O

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Under suitable conditions, SCl₂ reacts with water to produce a yellow precipitate of sulfur and a solution A. Solution A contains a mixture of SO₂ (aq) and compound B.

What is the oxidation number of sulfur in SCl₂?

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This question looks at different redox reactions.

For each of the equations below, write the oxidation number of the element printed in bold  underneath its symbol, and balance the equation by adding appropriate numbers before each species.

What would you see happening in the reaction shown in (a)(ii)?

Zinc with displace copper from copper sulfate solution.

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Use a half equation to explain what species is acting as the oxidising reagent in the reaction in (c).

Household bleach contains NaClO as its active ingredient.

NaClO can be produced from the reaction between chlorine and water.

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The balanced symbol equation showing the reaction of chlorine and sodium hydroxide to form NaClO is shown below.

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The concentration of NaClO in bleach can be found by reacting it with hydrogen peroxide, H₂O₂.

NaClO (aq) + H₂O₂ (aq) → NaCl (aq) + O₂ (g) + H₂O (l)

Explain, using oxidation numbers, why chlorine has been reduced in this reaction.

A student reacted an excess of aqueous hydrogen peroxide to 10.0 cm³ of a sample of bleach. They collected 108 cm³ of oxygen gas.

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This question is about the tetrathionate ion.

The tetrathionate ion is shown in Fig 1.1.

Calculate the oxidation number of sulfur in the tetrathionate ion. Explain your answer.

Sodium tetrathionate can be formed by reacting sodium thiosulfate, Na₂S₂O₃, with iodine.

Sodium tetrathionate can also be made by reacting sodium bisulfite, NaHSO₃, with disulfur dichloride, S₂Cl₂.

Explain if this reaction can be described as a disproportionation reaction. Include reference to oxidation numbers of sulfur in your answer.

Write equations for the processes involved in the darkening of photochromic glasses and explain if each reaction is reduction or oxidation.

Prescription photochromic sunglasses react to ultraviolet light and are adjusted to the needs of the wearer.

Explain why someone wearing photochromic sunglasses might not receive the full benefit of the glasses when driving a car on a cold, bright day.

The darkening process caused by the formation of silver atoms is reversible.

Write two equations to show how copper(I) chloride can react with the products from part (a) to remove the silver atoms and cause the lens to lighten.

Copper(I) chloride, similar to that used in photochromic glass, can be made in the laboratory by the following method:

• Warm 0.5 g copper(II) oxide with 5 cm³ concentrated hydrochloric acid for 1 minute.
• Add 1.0 g of copper turnings.
• Gently boil for 5 minutes.
• Filter the solution into 250 cm³ of deionised water.
• Allow the copper(I) chloride precipitate to settle.
• Decant the liquid.
• Allow the copper(I) chloride to dry.

Complete Table 3.1 by identifying which products are formed by oxidation or reduction. 

Sulfur dioxide reacts with a solution of copper(II) chloride.

Identify the reducing agent and oxidising agent in this reaction.

Sodium iodate is one of the main sources of iodine in the world. To extract the iodine, sodium iodate is reacted with sodium hydrogen sulfite, NaHSO₃, according to the following ionic equation.