This question is about the development of lithium cells. The value of E° for lithium suggests that a lithium cell could have a large EMF. Table 9 shows some electrode potential data. Table 9 | Reaction | E° / V | |--------------------------------------|--------| | Li+(aq) + e- → Li(s) | -3.04 | | 2H2O(l) + 2e- → H2(g) + 2OH-(aq) | -0.83 | | 1/2 H2(g) → H+(aq) | 0.54 | 0 9.1 Use data in Table 9 to explain why an aqueous electrolyte is not used for a lithium cell. 0 9.2 In the 1970s lithium-iodine cells became a common power source for heart pacemakers. Lithium iodide is the final product of the cell reaction. Use data in Table 9 to calculate the cell EMF of a standard lithium-iodine cell. 0 9.3 An EMF value for a commercial lithium-iodine cell is 2.80 V Suggest why this value is different from the value calculated in Question 0 9.2. 0 9.4 In some lithium cells, lithium perchlorate (LiClO4) is used as the electrolyte. Deduce the oxidation state of chlorine in LiClO4. 0 9.5 In other lithium cells, lithium cobalt oxide electrodes and lithium electrodes are used. Give an equation for the reaction that occurs at the positive lithium cobalt oxide electrode. 0 9.6 Give an equation for the reaction that occurs at the negative lithium electrode.

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This question is about the development of lithium cells - AQA - A-Level Chemistry - Question 9 - 2021 - Paper 1

Question 9

This question is about the development of lithium cells. The value of E° for lithium suggests that a lithium cell could have a large EMF. Table 9 shows some electro... show full transcript

Worked Solution & Example Answer:This question is about the development of lithium cells - AQA - A-Level Chemistry - Question 9 - 2021 - Paper 1

Step 1

Use data in Table 9 to explain why an aqueous electrolyte is not used for a lithium cell.

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Answer

Lithium has a standard electrode potential ( E° ) of -3.04 V, which indicates that it is more negative than both the reduction potential of water and the EMF of 2.21 V. As a result, lithium would react with the water in an aqueous electrolyte, either by oxidizing to Li+ or by reducing water to hydrogen gas, leading to undesirable reactions.

Step 2

Use data in Table 9 to calculate the cell EMF of a standard lithium-iodine cell.

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Answer

To calculate the cell EMF, we find the reaction of lithium and iodine. Considering the standard potentials, we can add lithium’s E° value and the E° for reduction of iodine. The EMF of the cell can be calculated as follows:

$E_{cell} = E°(Li^+/Li) + E°(I_2/I^-)$

Thus:

$E_{cell} = (-3.04 ext{ V}) + (0.54 ext{ V}) = -2.50 ext{ V}$

Step 3

Suggest why this value is different from the value calculated in Question 0 9.2.

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Answer

The discrepancy between the calculated EMF value of -2.50 V and the commercial EMF of 2.80 V could be attributed to non-standard conditions such as concentration, temperature, or the presence of stabilizing agents in the commercial cell that enhance the overall voltage produced.

Step 4

Deduce the oxidation state of chlorine in LiClO4.

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In lithium perchlorate (LiClO4), lithium has a +1 oxidation state. The overall charge of the molecule is neutral, thus the oxidation state of chlorine can be calculated by considering that the four oxygen atoms each have a -2 oxidation state. Therefore, the oxidation state of chlorine must be +7 to balance the overall charge:

$+1 + x + (4 imes -2) = 0 \implies x = +7$

Step 5

Give an equation for the reaction that occurs at the positive lithium cobalt oxide electrode.

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Answer

The reaction at the positive lithium cobalt oxide electrode can be represented as:

$LiCoO_2 + Li^+ + e^- \rightarrow Li_2CoO_2$

Step 6

Give an equation for the reaction that occurs at the negative lithium electrode.

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Answer

At the negative lithium electrode, the reduction reaction can be expressed as follows:

$Li^+ + e^- \rightarrow Li(s)$

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This question is about the development of lithium cells - AQA - A-Level Chemistry - Question 9 - 2021 - Paper 1

Worked Solution & Example Answer:This question is about the development of lithium cells - AQA - A-Level Chemistry - Question 9 - 2021 - Paper 1

Use data in Table 9 to explain why an aqueous electrolyte is not used for a lithium cell.

Use data in Table 9 to calculate the cell EMF of a standard lithium-iodine cell.

Suggest why this value is different from the value calculated in Question 0 9.2.

Deduce the oxidation state of chlorine in LiClO4.

Give an equation for the reaction that occurs at the positive lithium cobalt oxide electrode.

Give an equation for the reaction that occurs at the negative lithium electrode.

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