A Level Chemistry 2017 Paper 1 Question 30 Solution - Exclusive

Time flies and we are finally at our last question for this solution series! :)

In this exclusive video we want to discuss the suggested solution for A Levels Chemistry (H2 Chemistry) 2017 Paper 1 Question 30.

Let's take a look at this question:

2017 A Level H2 Chemistry P1 Q30 question

The topic tested in this question is on Electrochemistry, in particular the concept on Hydrogen-Oxygen Fuel Cell.

Let's do a very brief recap:

2017 A Level H2 Chemistry P1 Q30 hydrogen oxygen fuel cell overall reaction

H2 is oxidised and O2 is reduced to water in the overall reaction.

1. Determine Direction of Electron Flow

2017 A Level H2 Chemistry P1 Q30 deduce direction of electron flow

Since H2 is oxidised, electrode X will be the anode and is negatively charged for an electrochemical cell.

O2 is reduced and electrode Y will be the cathode and hence it will be positively charged.

This means direction of electron flow will be from anode X to cathode Y.

We can then look through the options and eliminate options C and D.

2017 A Level H2 Chemistry P1 Q30 eliminate C n D

2. Determine E value of Oxygen Electrode

Since O2 is reduced, we need to choose the relevant half equations from the Data Booklet where O2 is on the left-hand side of the half equation.

Also, the electrolyte is alkaline NaOH, so we also need to choose the half equation which contains OH-.

2017 A Level H2 Chemistry P1 Q30 choosing reduction of O2 in alkaline medium

From the Data Booklet we should be able to find these 2 half equations where O2 is on the left-hand side, hence undergoes reduction.

2017 A Level H2 Chemistry P1 Q30 half equations for O2

The first half equation where E0 = +1.23V should be used for acidic medium due to presence of H+.

The second half equation where E0 = +0.40V should be used for alkaline medium due to presence of OH-.

For this question we should be using the half equation in alkaline medium, where E0 = +0.40V.

Finally we can look at the options and choose option A as the correct answer to this question.

2017 A Level H2 Chemistry P1 Q30 compare option A n B

Check out this video for the full solution and detailed explanation!

Topic: Electrochemistry, Physical Chemistry, A Level Chemistry, Singapore

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