ElectrochemistryHard
Question
Chromium plating can involve the electrolysis of an electrolyte of an acidified mixture of chromic acid and chromium sulphate. If during electrolysis the article being plated increases in mass by 2.6 g and 0.6 dm3 of oxygen are evolved at an inert anode, the oxidation state of chromium ions being discharged must be: (assuming atomic weight of Cr = 52 and 1 mole of gas at room temperature and pressure occupies a volume of 24 dm3)
Options
A.-1
B.Zero
C.+1
D.+2
Solution
4H+ → O2 + 2H2O + 4e- ⇒ 1 mol ≡ 4F
⇒
mol ≡ 4 × = 0.1F
Cr3+ xe- → Cr(3 - x)+
⇒ 1 mol ≡ x F ⇒
mol ≡ 
F ≡ 0.1 F ⇒ x = 2
⇒ Oxidation state of Cr(3 - 2) = Cr+1 = + 1.
⇒
mol ≡ 4 × = 0.1FCr3+ xe- → Cr(3 - x)+
⇒ 1 mol ≡ x F ⇒
mol ≡ F ≡ 0.1 F ⇒ x = 2⇒ Oxidation state of Cr(3 - 2) = Cr+1 = + 1.
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