Question

500 mg of a dry adsorbent is added to a beaker containing 100 mL solution of concentration 100 mg phenol/(L solution). The adsorbent is separated out after 5 h of rigorous mixing. If the residual concentration in the solution after separating the adsorbent is 30 mg phenol/(L solution), the amount of phenol adsorbed (in mg per gram of dry adsorbent) is:

• A. 7
• B. 14
• C. 28
• D. 18

Hint:

When calculating adsorption, always subtract the final concentration from the initial concentration, and divide by the mass of the adsorbent to get the adsorption capacity.

Answer 1

The Correct Option is B

The amount of phenol adsorbed by the adsorbent can be calculated by comparing the initial amount of phenol in the solution and the final residual concentration after adsorption.

Step 1: Initial amount of phenol in the solution
The initial concentration of phenol in the solution is 100 mg/L, and the volume of the solution is 100 mL (0.1 L). Therefore, the initial amount of phenol in the solution is:

\[ \text{Initial phenol} = 100 \, \text{mg/L} \times 0.1 \, \text{L} = 10 \, \text{mg} \]

Step 2: Final amount of phenol in the solution
The residual concentration of phenol after adsorption is 30 mg/L. Therefore, the final amount of phenol in the solution is:

\[ \text{Final phenol} = 30 \, \text{mg/L} \times 0.1 \, \text{L} = 3 \, \text{mg} \]

Step 3: Amount of phenol adsorbed
The amount of phenol adsorbed is the difference between the initial and final amounts of phenol:

\[ \text{Phenol adsorbed} = 10 \, \text{mg} - 3 \, \text{mg} = 7 \, \text{mg} \]

Step 4: Amount of phenol adsorbed per gram of dry adsorbent
The mass of the dry adsorbent is 500 mg, which is 0.5 g. The amount of phenol adsorbed per gram of adsorbent is:

\[ \frac{\text{Phenol adsorbed}}{\text{Mass of adsorbent}} = \frac{7 \, \text{mg}}{0.5 \, \text{g}} = 14 \, \text{mg/g} \]

Therefore, the correct answer is: 14 mg per gram of dry adsorbent.