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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 2 months ago)
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.

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(edited 2 months ago)
Reply 2
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 2 months ago)

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