2021 P1 Q29 - Determine Redox Reaction between Zn and VO2+

Let's take a look at 2021 A Levels H2 Chemistry Paper 1 Question 29.

2021 p1 q29 question

We need to determine the redox reaction when excess zinc is added to acidified VO2+ ions.

In the options vanadium can be reduced to different oxidation states.

Let us find all the relevant half equations in the data booklet.

2021 p1 q29 E values for Zn and V

Notice zinc metal can be oxidised to Zn2+.

VO2+ (+5 oxidation state) can be reduced to VO2+ (+4 oxidation state).

VO2+ can then be further reduced to V3+, V3+ can be reduced to V2+, and finally V2+ reduced to vanadium metal.

Therefore we need to calculate the Ecell for each stage of reduction of vanadium species to determine its extent of reduction.

2021 p1 q29 calculate Ecell

Ecell for redox reactions between Zn and VO2+ (+5 oxidation state), VO2+ (+4 oxidation state) and V3+ are all positive. This means all these reactions are feasible and VO2+ can be reduced all the way to V2+.

Ecell for redox reaction between Zn and V2+ is negative. This means Zn cannot reduce V2+ to vanadium metal.

Therefore the final oxidation state of vanadium should be V2+ and answer to this question is option C.

2021 p1 q29 answer

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

Back to list of questions for 2021 A Level H2 Chemistry Paper 1.

Found this A Level Chemistry video useful?

Please LIKE this video and SHARE it with your friends!

Join my 17,000 subscribers on my YouTube Channel for new A Level Chemistry video lessons every week.

Check out other A Level Chemistry Video Lessons here!

Need an experienced tutor to make Chemistry simpler for you?

Do consider signing up for my JC Chemistry Tuition classes at Bishan or on-demand video lessons!