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Q.
A solution of copper (II) sulphate (VI) is electrolysed between copper electrodes by a current of $10.0\, A$ for exactly $9650\, s$. Which remains unchanged?
Electrochemistry
Solution:
$CuSO_{4} \rightarrow Cu ^{2+}( aq )+ SO _{4}^{2-}$
Electrons are made of copper. Thus Oxidatic
$Cu ( s ) \longrightarrow Cu ^{2+}( aq )+2 e$
$Cu ^{2+}( aq )+2 e ^{-} \longrightarrow Cu ( s )$
Reduction Copper formed $= w$
$w=z i t=\frac{63.5 \times 10.0 \times 9650}{2 \times 96500} g$
$=\frac{63.5}{2 \times 63.5}=0.5\, mol$
$0.5$ mole of copper is dissolved from the anode. Thus, its mass decreases. $0.5$ mole of copper from the anode is deposited at the cathode. Thus, its mass increases. Thus, molar concentration of aqueous solution of $CuSO _{4}$ remains unchanged.