In the previous blogpost, we have discussed on the 2nd criterion for predicting products of electrolysis for aqueous solutions under the Series on “Secrets of Redox and Electrolysis“.
Today we will end the series by introducing the 3rd criterion:
Consider: Nature of Electrodes Used in Electrolysis
Different products are discharged at the electrode when different type of electrodes are used.
When we say different types of electrodes used, it simply means:
Inert Electrode (such as Carbon and Platinum) vs Reactive Electrode (such as Cu or Silver)
We shall once again look at it in a step-by-step simplified approach.
Lets consider 2 electrolysis reactions using Copper(II) Sulphate as the electrolyte.
Set-Up A: Inert Electrodes such as Platinum
At the +ve Anode:
- 4OH–(aq) –> 2H2O(l) + O2(g) + 4e–
- SO42- ions remain in solution
At the -ve Cathode:
- Cu2+(aq) + 2e– –> Cu(l)
- H+ ions remain in solution
Summary:
- Overall reaction is: 2CuSO4(aq) + 2H2O(l) –> 2Cu(s) + O2(g) + 2H2SO4(aq)
- Acidic solution of H2SO4(aq) formed at end of reaction
Set-Up B: Reactive Electrodes such as Copper
At the +ve Anode:
- Cu(s) –> Cu2+(aq) + 2e–
- Anode dissolves to form Cu2+ ions in aqueous solution
At the -ve Cathode:
- Cu2+(aq) + 2e– –> Cu(l)
- H+ ions remain in solution
- Cathode becomes coated with a layer of reddish-brown Cu
Summary:
- Cu is transferred from the anode to the cathode
- Cu cathode slowly increases in mass
- Cu anode decreases in mass
- Colour & Concentration of CuSO4 remain unchanged
- No effective loss of Cu2+ ions from the CuSO4 solution
Let’s check out 1 question to see how much you understand.
Question:
Aqueous copper(II) sulphate is electrolyzed using copper electrodes. Which observations will be made?
Anode (+ve) Cathode (-ve) the electrolyte A. anode dissolves pink solid forms blue colour fades B. anode dissolves pink solid forms no change C. colourless gas forms colourless gas forms no change D. colourless gas forms pink solid forms blue colour fades
PS: Remember to leave down your answers in the “Leave A Reply” section below.
PPS: To learn everything on Redox & Electrolysis, please visit the section right below called “Table of contents for Secrets of Redox & Electrolysis“
Related Articles:
- O Level Chemistry – Definitions of Electrolysis
- O Level Chemistry – Strategies to Predict Products of Electrolysis for Aqueuous Solutions
- O Level Chemistry: Mole Concepts / Qualitative Analysis
- O Level Chemistry – Strategies to Predict Products of Electrolysis for Aqueuous Solutions
- O Level Chemistry – Products of Electrolysis of Molten Compound
Mark Harrington says
Both Copper Electrodes with H2so4
ritchiemohammed says
C5H11COOH+C8H14OH>>>>CH3CH2CH2CH2CH2COOC8H14+H2O
IS THIS REACTION POSSIBLE
ritchie mohammed says
Cus04 give a pink solid and with ————-> ?
sean says
Well Done heeko.
Keep up the good understanding of Chemistry.
To Your Academic Success in Chemistry,
Sean
Master Trainer
heeko says
the answer is B as C and D are ruled out cuz no gas can be formed as copper is less reactive the hydrogn, oxygen or sulfate. and the colour does nt fade away cuz the concentration of copper is kept constant due to the dissolvin anode!
sean says
I am glad you got the point.
Happy learning. Chemistry is in fact very easy once your build up a strong foundation of the ESSENTIAL CONCEPTS. The rest is largely by application & association. Memorizing is only about 15% or less when you are well versed in the concepts.
To Your Academic Success in Chemistry,
Sean
Master Trainer
Author
Lily says
The answer is definately B .Thankyou very much. I understood the point immediately!
sean says
Hi Raymond,
Well Done. Keep up the good work.
Cheers
Sean
Master Trainer
Author
Raymond says
The answer is B