Multiple Choice
The titration of 18.0 mL of an unknown diprotic acid requires 15.3 mL of 0.120 M KOH solution to reach the equivalence point. What is the concentration of the unknown acid sample?
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18. Aqueous Equilibrium
Titrations: Diprotic & Polyprotic Buffers
Multiple Choice
Suppose you have 50.1 mL of a H3PO4 solution that you titrate with 15.4 mL of 0.10 M KOH solution to reach the endpoint. What is the concentration of H3PO4 of the original H3PO4 solution?
A
0.00200 M
B
0.00154 M
C
0.00649 M
D
0.0307 M
Verified step by step guidance1
Write the balanced chemical equation for the reaction: \( \text{H}_3\text{PO}_4 + 3\text{KOH} \rightarrow \text{K}_3\text{PO}_4 + 3\text{H}_2\text{O} \). This shows that one mole of \( \text{H}_3\text{PO}_4 \) reacts with three moles of \( \text{KOH} \).
Calculate the moles of \( \text{KOH} \) used in the titration. Use the formula: \( \text{moles of KOH} = \text{volume (L)} \times \text{molarity (M)} \). Convert 15.4 mL to liters by dividing by 1000.
Determine the moles of \( \text{H}_3\text{PO}_4 \) that reacted. Since the stoichiometry from the balanced equation is 1:3, divide the moles of \( \text{KOH} \) by 3 to find the moles of \( \text{H}_3\text{PO}_4 \).
Calculate the concentration of \( \text{H}_3\text{PO}_4 \) in the original solution. Use the formula: \( \text{concentration (M)} = \frac{\text{moles of } \text{H}_3\text{PO}_4}{\text{volume of solution (L)}} \). Convert 50.1 mL to liters by dividing by 1000.
Substitute the moles of \( \text{H}_3\text{PO}_4 \) and the volume of the solution into the concentration formula to find the molarity of the original \( \text{H}_3\text{PO}_4 \) solution.
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