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Q. A quantity of electrical charge that brings about the deposition of $4.5 \, Al$ from $A l ^{3+}$ at the cathode will also produce the following volume at (STP) of $H _{2}(g)$ from $H ^{+}$ at the cathode

Bihar CECEBihar CECE 2013Electrochemistry

Solution:

$2 H ^{+}+2 e^{-} \longrightarrow H _{2}$
$A ^{3+}+3 e ^{-} \longrightarrow Al$
$\frac{w\left(H_{2}\right)}{w(A l)}=\frac{E\left(H_{2}\right)}{E(A l)}=\frac{1}{9}$
$w\left( H _{2}\right)=4.5 \times \frac{1}{9}=0.5\, g =\frac{1}{4} \,mol\, H _{2}$
$=\frac{22.4}{4}=5.6\, LH _{2}$ at STP