3 Oxidation - Reduction Problems Chemistry (Any help is great, thanks so much!)?

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2018-05-13 3:36 am

1) What is happening when copper ion plates out as copper onto baby shoes as they are preserved?

A) Energy as heat is converted to energy of motion.
B) Energy of motion is converted to energy as heat.
C) Chemical energy is converted to electrical energy.
D) Electrical energy is converted to chemical energy.

2) Calculate the E° for the reaction:

MnO2 + 4H+ + 2I– → Mn2+ + 2H2O + I2.
MnO2 + 4H+ + 2e– → Mn2+ + 2H2O E° = +1.229 V
I2 + 2e– → 2I– E° = + 0.534 V

A) –1.76 V
B) –0.695 V
C) 1.76 V
D) 0.695 V

3) If 30 mL of 0.112 M permanganate solution are required to reach the equivalence point in a titration with 21 mL of iron (II) ion solution, what is the molarity of the iron (II) solution?

Iron (II) ion reacts with permanganate ion in the following balanced redox equation in acid solution.

8H+ + 5Fe2+ + MnO4– → 5Fe3+ + Mn2+ + 4H2O

A) 0.392 M
B) 0.032 M
C) 0.160 M
D) 0.800 M

回答 (1)

wanszeto

2018-05-13 7:41 pm

✔ 最佳答案

1)
The reaction takes place at the cathode of the electrolytic cell.
Cu²⁺ + 2e⁻ → Cu

The chemical change is caused by electricity. In other words, electrical energy is converted to chemical energy.

The answer: D) Electrical energy is converted to chemical energy.

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2)
E°(reaction)
= E°(reduction) - E°(oxidation)
= (+1.229 V) - (+0.534 V)
= +0.695 V

The answer: D) 0.695 V

====
3)
8H⁺ + 5Fe²⁺ + MnO₄⁻ → 5Fe³⁺ + Mn²⁺ + 4H₂O
Mole ratio Fe²⁺ : MnO₄⁻ = 5 : 1

No. of milli-moles of MnO₄⁻ ion = (0.112 mmol/mL) × (30 mL) = 3.36 mmol
No. of milli-moles of Fe²⁺ ion = (3.36 mmol) × (5/1) = 16.8 mmol
The molarity of Fe²⁺ solution = (16.8 mmol) / (21.0 mL) = 0.800 M

The answer: D) 0.800 M

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