A conductivity cell with two electrodes (dark side) are half filled with infinitely dilute aqueous solution of a weak…
Electrochemistry · Class 12 · JEE Main Previous Year Question
A conductivity cell with two electrodes (dark side) are half filled with infinitely dilute aqueous solution of a weak electrolyte. If volume is doubled by adding more water at constant temperature, the molar conductivity of the cell will:
- a
decrease sharply
- b
increase sharply
- c✓
remain same or cannot be measured accurately
- d
depend upon type of electrolyte
remain same or cannot be measured accurately
Strategy: Analyze the behavior of conductivity in the limit of infinite dilution for weak electrolytes.
Con\ceptual Analysis:
- Infinite Dilution: By definition, at infinite dilution, the \degree of dissociation () has already reached its maximum value ().
- Conductivity () vs. Molar Conductivity (): Further adding water decreases the number of ions per unit volume, making approach zero.
- Molar Conductivity: is a constant for a given pair of ions. Doubling the volume from an already "infinite" state doesn't change or the ion speed.
Special Case (Half-filled cell): If a cell with fixed electrodes is only half filled, the geometric cell constant is undefined or doubled in the empty region. Adding water to fill the cell changes the cross-sectional area of the conductor (the solution) between the electrodes, but doesn't change the substan\ce's intrinsic . Measurement at such low concentrations is extremely difficult.
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