When water is electrolyzed for 30 minutes it is observed that colourless gases P and Q forms in the test tubes put on the electrodes. The gas P forms at double speed to that of Q.
(i) Name the gases P and Q and write the type of the reaction.
(ii) Name the electrodes at which P and Q forms.
(iii) When gas P reacts with CuO (cupric oxide) it gives brown solid (1) and vapours of (2).
The vapous of (2) change anhydrous CuSO4 to blue colour.
Write the reaction for this process and identify 1 and 2
(iv) When gas Q reacts with brown solid formed in above question it forms black coloured solid (Z). Write the reaction for this process and identify solid (Z)
Answers
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When electric current is passed through water , it decomposes to give hydrogen gas and oxygen gas.
ELECTRICITY
2H₂O(I) ---------------------------- > 2H₂(g) + O₂(g)
At cathode :
H+ ions will gain electrons and form Hydrogen gas
2H⁺ +2e--->H2 (g)
At anode : Oxygen gas will be released
4 OH⁻(aq)→O2(g) + 2 H2O(l) + 4 e−
II) The volume of hydrogen gas collected at cathode is more than volume of oxygen gas at anode because water is made up of 2 parts of hydrogen and 1 part of oxygen by volume.
iii) If dil.H2SO4 is added to water then the rate of electrolysis increases.
In the electrolysis of water
(a) the gas is collected at cathode is Hydrogen , H₂
And the gas collected at anode is oxygen ,O₂
(b) first of all we should we reaction between Hydrogen and oxygen to form water :- 2H₂ + O₂ ⇔ 2H₂O
you can see that, 2moles of H₂ and 1 mole of O₂ react to form 2moles of H₂O
we can also say that , if we break 2moles of water (using electrolysis ) , we gain 2hole of H₂ and one mole of O₂
Here, P, T, are constant ,
So, Volume is directly proportional to number of moles
∴ if we break 2V of water, we get 2V of H₂ and 1V of O₂ .
That's why the volume is collected at one electrode is double than other .
(iii) A pure water is not good conductor of Electricity . when dil H₂SO₄ is not added then electrolysis of pure water can't be possible .