Cobalt is a transition element that forms complex ions with oxidation states +2 and +3. Explain what is meant by the term transition element. The following scheme shows some reactions of [Co(H2O)6]2+: OH-(aq) ⟶ precipitate A excess Cl-(aq) ⟶ solution of B excess NH3(aq) ⟶ solution of C (i) State the formula of each of the following. A B C (ii) State the colour of the following solutions. [Co(H2O)6]2+ solution of B solution of C (c) Define the term standard electrode potential. An electrochemical cell was set up to measure the standard electrode potential, E°cell, of a cell made of a Co2+/Co half-cell and a Fe2+/Fe half-cell. (i) Complete the table with the substance used to make the electrode in each of these half-cells. half-cell electrode Co2+/Co Fe2+/Fe (ii) Write the equation for the overall cell reaction. (iii) Use the Data Booklet to calculate the E°cell. The electrochemical cell in (d) was set up again but this time the concentration of Co2+(aq) was 0.050 mol dm−3. The Nernst equation can be used to calculate the value of an electrode potential at different concentrations. E = E° + (0.0591/z)log[Co2+(aq)] (i) Use the Data Booklet and the Nernst equation to calculate the value of E for the Co2+/Co half-cell in this experiment. (ii) Suggest how this change will affect the overall cell potential, E°cell, compared to E°cell in (d)(ii). Circle your answer. less positive no change more positive (f) Iron(III) ions can oxidise vanadium metal. Write an equation for the reaction of an excess of iron(III) ions with vanadium metal. Use the Data Booklet for help.

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Cobalt is a transition element that forms complex ions with oxidation states +2 and +3 - CIE - A-Level Chemistry - Question 4 - 2016 - Paper 1

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Cobalt is a transition element that forms complex ions with oxidation states +2 and +3. Explain what is meant by the term transition element. The following scheme s... show full transcript

Worked Solution & Example Answer:Cobalt is a transition element that forms complex ions with oxidation states +2 and +3 - CIE - A-Level Chemistry - Question 4 - 2016 - Paper 1

Step 1

Explain what is meant by the term transition element.

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Answer

A transition element is defined as an element that forms one or more stable ions or compounds with partially filled or incomplete d orbitals. This characteristic allows for various oxidation states and complex ion formation.

Step 2

State the formula of A.

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Answer

[Co(OH)4(H2O)2] - This formula represents the precipitate formed when hydroxide ions are added.

Step 3

State the formula of B.

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Answer

[CoCl4]2- - This formula represents the complex ion formed in the solution after adding excess chloride ions.

Step 4

State the formula of C.

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Answer

[Co(NH3)6]2+ - This formula represents the complex formed when excess ammonia is added.

Step 5

State the colour of the following solutions.

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Answer

[Co(H2O)6]2+ - Pink; solution of B - Blue; solution of C - Brown/yellow-orange.

Step 6

Define the term standard electrode potential.

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Answer

The standard electrode potential (E°) is the electromotive force (emf) of an electrochemical cell compared to a standard hydrogen electrode at a concentration of 1 mol dm−3 and a pressure of 1 atm (or in Pa) at 298 K.

Step 7

Complete the table with the substance used to make the electrode in each of these half-cells.

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Answer

Co2+/Co - Co/cobalt; Fe2+/Fe - Pt/carbon/graphite.

Step 8

Write the equation for the overall cell reaction.

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Answer

Co2+ + 2e⁻ ⇌ Co; Fe²⁺ + 2e⁻ ⇌ Fe +V^3+.

Step 9

Use the Data Booklet to calculate the E°cell.

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Answer

E°cell = 0.37 - (0.28) - (0.0591/2)log[Co²⁺] = 0.32 - 0.318 V.

Step 10

Use the Data Booklet and the Nernst equation to calculate the value of E for the Co2+/Co half-cell in this experiment.

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E = 0.32 + (0.0591/2)log[0.050] = 0.32 - 0.318 = 0.002 V.

Step 11

Suggest how this change will affect the overall cell potential, E°cell, compared to E°cell in (d)(ii).

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Answer

This change will result in a more positive E°cell.

Step 12

Write an equation for the reaction of iron(III) ions with vanadium metal.

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Answer

The equation is: 4Fe³⁺ + V → 4Fe²⁺ + V⁴⁺.

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Cobalt is a transition element that forms complex ions with oxidation states +2 and +3 - CIE - A-Level Chemistry - Question 4 - 2016 - Paper 1

Worked Solution & Example Answer:Cobalt is a transition element that forms complex ions with oxidation states +2 and +3 - CIE - A-Level Chemistry - Question 4 - 2016 - Paper 1

Explain what is meant by the term transition element.

State the formula of A.

State the formula of B.

State the formula of C.

State the colour of the following solutions.

Define the term standard electrode potential.

Complete the table with the substance used to make the electrode in each of these half-cells.

Write the equation for the overall cell reaction.

Use the Data Booklet to calculate the E°cell.

Use the Data Booklet and the Nernst equation to calculate the value of E for the Co2+/Co half-cell in this experiment.

Suggest how this change will affect the overall cell potential, E°cell, compared to E°cell in (d)(ii).

Write an equation for the reaction of iron(III) ions with vanadium metal.

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