IGCSE Chemistry electrolysis

Could you please explain why D is the correct answer for this question?
At the cathode, H ions will be discharged so shouldn't the color at cathode be red (acidic)?

(edited 4 months ago)

Reply 1

charco

Study Forum Helper

Original post by S0303

Could you please explain why D is the correct answer for this question?
At the cathode, H ions will be discharged so shouldn't the color at cathode be red (acidic)?

Before electrolysis there are H⁺ and OH^- ions at equal concentration due to the auto-dissociation of water.

If H⁺(aq) ions are removed as they become reduced to H₂(g) then only the OH^-(aq) ions remain.

So the indicator turns blue.

-----------------------------------------------------------------------------------------------
Signature
[url=https://www.colourful-solutions.com] Colourful Solutions IB Chemistry Testing and Notes

(edited 4 months ago)

Reply 2

Scanjo63

Chlorine will bleach litmus colourless
sodium hydroxide a strong alkali is formed at the cathode- so it will turn litmus blue

hydrogen gas and not hydrogen ions are formed at the cathode

try heref or more info|:
https://www.youtube.com/watch?v=N_HQGiC9OJE
https://www.science-revision.co.uk/electrolysis%20of%20solutions%20heading.html

(edited 4 months ago)