Q4(d). Selective electrodes and ionic activity
(i) Write the working principle of ion-selective electrode with an example. (ii) Using the Debye–Hückel limiting law, calculate the activity coefficients of sodium and sulfate ions, and the mean ionic activity coefficient of a 0.01 molal solution of sodium sulfate in water at room temperature. (5+5 marks)
Answer in brief
An ion-selective membrane responds to the activity of a selected ion. At 25 °C, the limiting-law estimates are γ_Na = 0.816, γ_SO₄ = 0.444 and γ± = 0.666.
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Coversion-selective electrodeglass electrodeDebye–Hückel limiting lawmean ionic activity coefficientionic strength
All parts of Question 4
- 4(a) Translational entropy of nitrogen10 marks
- 4(b) Chemical potential versus temperature10 marks
- 4(c) Cell voltage under load and electrolysis10 marks
- 4(d) Selective electrodes and ionic activity10 marks