When 200 mL of 0.2 M acetic acid is shaken with 0.6 g of wood charcoal, the final concentration of acetic acid after adsorption is 0.1 M. The mass of acetic acid adsorbed per gram of carbon is ____________ g.

Solution

Chemistry ma’am · 3 steps

The acid that disappeared from the solution is the acid now sitting on the charcoal, so find that drop first.

1. Moles adsorbed. The concentration fell from 0.2 M to 0.1 M in 200 mL = 0.2 L. The moles removed are 0.2 × (0.2 - 0.1) = 0.02 mol.
2. Convert to grams. The molar mass of acetic acid, CH₃COOH, is 60 g mol⁻¹. So the mass adsorbed is 0.02 × 60 = 1.2 g.

   x/m = (1.2 g)/(0.6 g) = 2

3. So. Each gram of charcoal holds 2 g of acetic acid.

The common slip: 1.2. Stopping at the total mass adsorbed gives 1.2, not 2. The question asks per gram, so divide by the 0.6 g of charcoal.

The idea to keep. Amount adsorbed is always (initial minus final concentration) times volume. Turn it into grams, then divide by the adsorbent mass to get x/m.

Answer from the NTA final answer key. Solution by PrepWiser.