Ascorbate and copper ions have the following electrochemical potentials: Dehydro

Question

Ascorbate and copper ions have the following electrochemical potentials: Dehydroascorbate + 2H+ +2e??Ascorbate ???=+0.08V Cu2+ +e??Cu+ ???=+0.159V 10 mL of a 0.02 M solution of ascorbate in a buffered solution at pH7 at 25?C is mixed with 10 mL of 0.02 M of Cu2+.

Part A

Choose the correct balanced chemical equation for the reaction.

Part B

Figure out the equilibrium concentration of dehydroascorbate.

Part C

Figure out the equilibrium concentration of ascorbate.

Part D

Figure out the equilibrium concentration of Cu2+.

Part E

Figure out the equilibrium concentration of Cu+.

O Dehydroascorbate 2H+ e- Cu2+ Ascorbate Cu O 2+ Ascorbate Cut Dehydroascorbate H O 2Cu Ascorbate 20 ut Dehydroascorbate 2H 2+ O Dehydroascorbate 2H 2Cu2 Ascorbate 2Cu

Explanation / Answer

Write down the two half reactions:

dehydroascorbate + 2 H+ + 2 e- ------> ascrobate; E0’ = +0.08 V

Cu2+ + 2 e- -----> Cu+; E0’ = +0.159 V

a) We need to write the equation in such a way that E0’cell has the highest value. We can clearly see that a positive E value will be obtained when Cu2+/Cu+ forms the reduction half. The oxidation half is

ascorbate -----> dehydroascorbate + 2 H+ + 2 e-; E0” = -0.08 V

The cell reaction is

2 Cu2+ + Ascorbate -----> 2 Cu+ + dehydroascorbate + 2 H+

E0’cell = E0’red + E0’ox = (+0.159 V) + (-0.08 V) = 0.079 V (ans).

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