Suppose 50.0 mL of an aqueous solution containing an unknown monoprotic weak
acid is titrated with 0.250 M KOH. The titration requires 31.52 mL of the potassium hydroxide
solution to reach the equivalence point. What is the concentration (in molarity) of the unknown
acid solution?
To find the concentration of the unknown acid solution, you need to start by determining the number of moles of KOH used in the titration.
First, convert the volume of KOH used to liters:
31.52 mL * (1 L / 1000 mL) = 0.03152 L
Next, use the balanced chemical equation between the unknown weak acid and KOH to find the mole ratio. Assuming the reaction is stoichiometric:
1 mole of unknown acid reacts with 1 mole of KOH.
Therefore, the number of moles of KOH used is equal to the number of moles of the unknown acid present in the 50.0 mL solution.
Now, calculate the number of moles of KOH used:
moles of KOH = concentration of KOH * volume of KOH used
moles of KOH = 0.250 M * 0.03152 L = 0.00788 mol
Since the stoichiometry between KOH and the unknown acid is 1:1, the number of moles of the unknown acid is also 0.00788 mol.
Next, calculate the concentration of the unknown acid in molarity:
concentration of unknown acid = moles of unknown acid / volume of acid solution
concentration of unknown acid = 0.00788 mol / 0.0500 L = 0.1576 M
Therefore, the concentration of the unknown acid solution is 0.1576 M.
HA + KOH --> H2O + KA
mols KOH = M x L = ?
mols HA = moles KOH (from the coefficients in the balanced equation.
M HA = moles HA/L HA