Question

At 25°C molar conductance of 0.1 molar aqueous solution of ammonium hydroxide is 9.54 ohm^-1 cm² mol^-1 and at infinite dilution its molar conductance is 238 ohm^-1 cm² mol^-1. The degree of ionisation of ammonium hydroxide at the same concentration and temperature is

• A. 2.080%
• B. 20.800%
• C. 4.008%
• D. 40.800%

Answer 1

The Correct Option is C

To determine the degree of ionisation of ammonium hydroxide (NH₄OH) at a specified concentration and temperature, we can employ the relationship between molar conductance at a given concentration and at infinite dilution.

The degree of ionisation (\( \alpha \)) can be calculated using the formula:

\[\alpha = \frac{\Lambda_c}{\Lambda_0}\]

where:

• \(\Lambda_c\) = molar conductance at concentration \( c \) (9.54 ohm^-1 cm² mol^-1)
• \(\Lambda_0\) = molar conductance at infinite dilution (238 ohm^-1 cm² mol^-1)

Substituting the given values into the formula, we get:

\[\alpha = \frac{9.54}{238}\]

Calculating the above expression gives:

\[\alpha = 0.04008\]

To express the degree of ionisation as a percentage, we multiply by 100:

\[\alpha\% = 0.04008 \times 100 = 4.008\%\]

Thus, the degree of ionisation of ammonium hydroxide at the given concentration and temperature is 4.008%.