50 ml of 1 M oxalic acid is shaken with 0.5g wood charcoal. The final concentration of the solution after adsorption is 0.5 M. What is the amount of oxalic acid adsorbed per gm of carbon ?

No. of moles in 50 ml of  1 M oxalic acid is =$\frac{50}{1000}\times 1=0.05\mathrm{moles}$ of oxalic acid

After adsorption, remaining moles of oxalic acid=$\frac{50}{1000}\times 0.5=0.025\mathrm{moles}$

Thus, moles that adsorb on charcoal is =0.05−0.025=0.025 moles of oxalic acid.

Therefore, 0.025 moles of oxalic acid adsorb on 0.5 g of charcoal.

1 gram of charcoal moles adsorb=$\frac{0.025}{0.5}=0.05$ moles of oxalic acid.

Amount of oxalic acid adsorbed per gram of charcoal = 0.05×126g/mole=6.30grams

Thus, 6.30 g of oxalic acid adsorb per gram of charcoal.