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Electrochemistry

Question
CBSEENCH12010050

Calculate emf of the following cell at 25 °C:

 Fe | Fe2+(0.001 M) || H+ (0.01 M) | H2 (g) (1 bar) | Pt(s)

 E°(Fe2+ | Fe) = –0.44 V E°(H+ | H2 ) = 0.00 V

Solution

For the given cell representation, the cell reaction will be Fe(s) + 2H+(aq) → Fe2+(aq) + H2(g)

 The standard emf of the cell will be
straight E subscript cell superscript 0 space equals straight E to the power of 0 space straight H to the power of plus divided by straight H subscript 2 space rightwards arrow space straight E to the power of 0 space Fe to the power of 2 plus end exponent divided by Fe

space rightwards double arrow space straight E subscript cell superscript space 0 end superscript space equals 0 minus left parenthesis negative 0.44 right parenthesis space equals 0.44 straight V

The space Nernst space equation space for space the space cell space reaction space at space 25 to the power of 0 space straight C space will space be space

straight E subscript cell space equals straight E subscript cell superscript 0 space minus fraction numerator 0.0591 over denominator 2 end fraction log space fraction numerator left square bracket Fe to the power of 2 plus end exponent right square bracket over denominator left square bracket straight H to the power of plus right square bracket to the power of 2 plus end exponent end fraction space

equals space 0.44 minus fraction numerator 0.059 over denominator 2 end fraction space log space fraction numerator 0.001 over denominator left parenthesis 0.01 right parenthesis squared end fraction

=0.44-0.02955(log10)

=0.44-0.02955(1)

=0.41045V 0.41V

 The Nernst equation for the cell reaction at 25 º C will be

=0.44-0.02955(log10)

=0.44-0.02955(1)

=0.41045V 0.41V