Practicing Success
Calculate the emf of the cell \(Pt, H_2 (1.0 atm) | CH_3COOH (0.1 M) || NH_3 (aq, 0.01M) | H_2 (1.0 atm), Pt,\) \(K_a (CH_3COOH) =1.8 × 10^{–5}, K_b (NH_3) = 1.8 × 10^{–5}\) |
–0.92 V –0.46 V –0.35 V –0.20 V |
–0.46 V |
The correct answer is option 2. –0.46 V. \(Pt| H_2 (1.0 atm) | CH_3COOH (0.1 M) || NH_3 (aq, 0.01M) | H_2 (1.0 atm)|Pt,\) \(K_a (CH_3COOH) =1.8 × 10^{–5}\) \(K_b (NH_3) = 1.8 × 10^{–5}\) \([H^+]_{CH_3COOH} = \sqrt{K_a \times C}\) \(⇒ [H^+]_{CH_3COOH} = \sqrt{1.8 \times 10^{-5} \times 0.1}\) \(⇒ [H^+]_{CH_3COOH} = 1.34 \times 10^{-3}\) Also, \([OH^-]= \sqrt{K_b\times C}\) \(⇒ [OH^-]= \sqrt{1.8 \times 10^{-5}\times 0.01}\) \(⇒ [OH^-]= 4.24 \times 10^{-4}\) And \([H^+]_{NH_4OH} = \frac{10^{-14}}{[OH^-]}\) \(⇒ [H^+]_{NH_4OH} = \frac{10^{-14}}{4.24 \times 10^{-4}}\) \(⇒ [H^+]_{NH_4OH} = 2.35 \times 10^{-11}\) \(E_{cell} = E^0_{cell} - \frac{0.0591}{n}log\frac{[H^+]_{CH_3COOH}}{[H^+]_{NH_4OH}}\) \(⇒E_{cell} = E^0_{cell} - \frac{0.0591}{1}log\frac{1.34 \times 10^{-3}}{2.35 \times 10^{-11}}\) \(⇒E_{cell} \approx -0.46\) |