A 11.0-mL sample of an unknown H3PO4 solution requires 116mL of 0.140 KOH to completely react with the H3PO4.
What was the concentration of the unknown H3PO4 solution (answer in M).
H3PO4(aq) + 3KOH(aq) --> 3H2O(l) + K3PO4(aq)
mols KOH = M x L = ?
mols H3PO4 = 1/3 mols KOH (look at the coefficients in the equation).
M H3PO4 = mols H3PO4/L H3PO4.
To find the concentration of the unknown H3PO4 solution, you can use the stoichiometry of the reaction and the volume of KOH solution required to react with it. Here's how to solve it step by step:
1. Write the balanced equation for the reaction:
H3PO4(aq) + 3KOH(aq) → 3H2O(l) + K3PO4(aq)
2. Determine the stoichiometric ratio between H3PO4 and KOH. According to the balanced equation, 1 mole of H3PO4 reacts with 3 moles of KOH.
3. Convert the volume of KOH solution to moles. The molarity (M) of a solution is given by moles of solute divided by the volume of the solution in liters.
Moles of KOH = molarity (KOH) × volume (KOH solution in liters)
= 0.140 M × 0.116 L
= 0.01624 moles
4. Apply the stoichiometric ratio to calculate the moles of H3PO4. Since the stoichiometric ratio is 1:3 between H3PO4 and KOH, the moles of H3PO4 will be one-third of the moles of KOH.
Moles of H3PO4 = (1/3) × moles of KOH
= (1/3) × 0.01624
= 0.00541 moles
5. Calculate the concentration of H3PO4. The concentration (M) is given by moles of solute divided by the volume of the solution in liters.
Concentration (H3PO4) = moles of H3PO4 / volume (H3PO4 solution in liters)
= 0.00541 moles / (11.0 mL ÷ 1000)
= 0.491 M
Therefore, the concentration of the unknown H3PO4 solution is 0.491 M.