Redox Reaction Worked Example 1

Let's take a look at this question on redox reactions and mole concept.

redox worked example question

First we need to figure out the balanced redox reaction.

Then we make use of the mole ratio to determine the amount of reactants and products left at the end of the reaction.

1. Balance Redox Reaction

Given Fe metal and Fe3+ ions react to form Fe2+ ions, we can determine that:

- Fe metal is oxidised to Fe2+
- Fe3+ is reduced to Fe2+

Hence we have 2 half equations and we can balance and add them together to get the overall redox reaction.

redox worked example balance redox equation

Check out this video if you are unsure about how to balance redox reactions via the half equation method.

2. Determine Resultant Mixture

Given the options in the question, we can systematically figure out the resultant mixture and see which option has the same amount of Fe3+ and Fe2+ ions.

The ICE table is an excellect way to figure this out quickly and concisely.

A. 1 mol Fe + 2 mol Fe3+

redox worked example option A

Exact amounts of reactants are used and the resultant mixture has no Fe3+ and 3 moles of Fe2+, hence not the answer.

B. 1 mol Fe + 3 mol Fe3+

redox worked example option B

Fe is limiting and resultant mixture has 1 mol Fe3+ and 3 mol Fe2+, hence not the answer.

C. 1 mol Fe + 5 mol Fe3+

redox worked example option C

Fe is limiting and resultant mixture has 3 mol Fe3+ and 3 mol Fe2+, hence this is the answer that we want.

D. 2 mol Fe + 3 mol Fe3+

redox worked example option D

Fe3+ is limiting and resultant mixture has no Fe3+ and 4.5 mol Fe2+, hence not the answer.

Topic: Redox Reactions, Physical Chemistry, A Level Chemistry, Singapore

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