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) → [Co(H2O)6]2+ + excess Cl−(aq) → precipitate A, solution of B, 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° + (0.059/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. (iii) 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.

A-Level CIE Chemistry 6.2 Transition Metals (A Level only): Cobalt is a transition element t

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

Question 4

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 d orbitals. These elements are typically characterized by their ability to engage in complex formation and exhibit various oxidation states.

Step 2

State the formula of A.

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Answer

[Co(OH)6]2−

Step 3

State the formula of B.

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Answer

[Co(H2O)6]2+

Step 4

State the formula of C.

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Answer

[Co(NH3)6]3+

Step 5

State the colour of the following solutions.

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Answer

[Co(H2O)6]2+: Blue solution of B: Pink solution of C: Yellow/orange

Step 6

Define the term standard electrode potential.

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Answer

The standard electrode potential (E°) is the emf (electromotive force) of an electrochemical cell under standard conditions, defined as 1 mol dm−3 concentration of all species and a pressure of 1 atm at a temperature of 298 K.

Step 7

Complete the table with the substance used to make the electrode.

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half-cell | electrode 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(s)

Step 9

Use the Data Booklet to calculate the E°cell.

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E°cell = 0.77 - 0.28 - 0.77 - 1.05 = -0.18 V

Step 10

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

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E for Co2+/Co = E° + (0.059/2) log [0.050] = -0.18 + (0.059/2) log(0.050) = -0.18 + 0.059/2 * (−1.3010) = -0.18 + 0.059 * (−0.6505) = -0.18 - 0.0383 ≈ -0.2183 V

Step 11

Suggest how this change will affect the overall cell potential.

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More positive

Step 12

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

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Answer

4Fe3+(aq) + V(s) → 4Fe2+(aq) + V4+(aq) + 2e−

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.

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.

Suggest how this change will affect the overall cell potential.

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

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