A 23.16 ml volume of an H2A acid solution of unknown concentration with 2 drops of phenolphthalein required 14.24 ml of 0.135 M NaOH to reach the endpoint. What is the molar concentration of the acid solution?
H2A + 2NaOH ==> Na2A + 2H2O
mols NaOH = M x L = ?
Convert mols NaOH to mols H2A using the coefficients in the balanced equation. So mols H2A = 1/2 mols NaOH
Then M H2A = mols H2A/L H2A
To find the molar concentration of the acid solution (H2A), we can use the concept of stoichiometry and the balanced chemical equation for the reaction between the acid and the base.
First, let's write the balanced equation for the reaction:
H2A + 2NaOH → Na2A + 2H2O
From the balanced equation, we can see that the molar ratio between H2A and NaOH is 1:2. This means that one mole of H2A reacts with two moles of NaOH.
Given that it took 14.24 ml of 0.135 M NaOH to reach the endpoint, we can calculate the number of moles of NaOH used in the reaction:
moles of NaOH = volume (in L) × concentration (in mol/L)
= 14.24 ml × (1 L / 1000 ml) × 0.135 mol/L
= 0.0019236 mol
Since the molar ratio between H2A and NaOH is 1:2, the number of moles of H2A will be half of the moles of NaOH used:
moles of H2A = 0.0019236 mol ÷ 2
= 0.0009618 mol
Now, let's calculate the molar concentration of the H2A acid solution:
Molar concentration of H2A = moles of H2A / volume of acid solution (in L)
= 0.0009618 mol / (23.16 ml × (1 L / 1000 ml))
= 0.0415 M
Therefore, the molar concentration of the acid solution (H2A) is 0.0415 M.