Question

50 mL of 1 M oxalic acid is shaken with 0.5gm of wood charcoal. The final concentration of the solution after adsorption is 0.5M. Amount of oxalic acid absorbed per gm of charcoal is:
A. 3.45gm
B. 3.15gm
C. 6.30g
D. none of these

Answer 1

Hint: In this question, first the number of moles of oxalic acid is calculated before and after adsorption in charcoal using the formula of molarity where number of moles is divided by volume of solution. Then the mass of oxalic acid is calculated by the formula where moles is equal to mass divided by molecular weight.

Complete step by step answer:
Given,
Volume of oxalic acid is 50mL.
Molarity of oxalic acid is 1M.
Mass of wood charcoal is 0.5gm.
Volume of oxalic acid after adsorbed is 0.5M.
To calculate the molarity number of moles of solute is divided by volume of solution.
The formula for calculating molarity is shown below.
\[M = \dfrac{n}{V}\]
Where,
M is the molarity
n is the number of moles
V is the volume.
To calculate the number of moles, substitute the values in the above equation.
\[ \Rightarrow 1M = \dfrac{n}{{0.05L}}\]
\[ \Rightarrow n = 1M \times 0.05L\]
\[ \Rightarrow n = 0.05mol\]
The remaining molarity after adsorption is 0.5 M, so the number of remaining moles is calculated as shown below.
\[ \Rightarrow 0.5M = \dfrac{n}{{0.05L}}\]
\[ \Rightarrow n = 0.5M \times 0.05L\]
\[ \Rightarrow n = 0.025mol\]
The number of moles of oxalic acid adsorbed by charcoal is calculated as shown below.
\[ \Rightarrow 0.05 - 0.025\]
\[ \Rightarrow 0.025\]
0.025 moles of oxalic acid will be adsorbed on 0.5g charcoal.
1 gm of charcoal will adsorb \[\dfrac{{0.025}}{{0.5}} = 0.05mol\] of oxalic acid.
The formula to calculate the number of moles is given below.
\[n = \dfrac{m}{M}\]
n is number of moles.
m is given mass.
M is molecular weight

The molecular weight of oxalic acid is 126g/mol.
To calculate the mass of oxalic acid, substitute the value in the equation.
\[ \Rightarrow 0.05mol = \dfrac{m}{{126g/mol}}\]
\[ \Rightarrow m = 0.05mol \times 126g/mol\]
\[ \Rightarrow m = 6.30g\]
Thus, the mass of oxalic acid absorb per gram of charcoal is 6.30g.

So, the correct answer is Option C.

Note: As you can see that the given volume is present in milliliters and the volume used in the formula is in terms of liters. So make sure to convert mL into L as molarity is calculated in terms of mol per liter.