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Calculate the concentration of a 785 ml NaOH solution if 1.17 l of 2.19 m H₃PO₄ is needed to titrate to the equivalence point.
Accepted Answer
To calculate the concentration of the NaOH solution, we can use the balanced chemical equation for the reaction between NaOH and H₃PO₄:
3NaOH + H₃PO₄ → Na₃PO₄ + 3H₂O
From the balanced equation, we can see that 3 moles of NaOH react with 1 mole of H₃PO₄. Therefore, the number of moles of NaOH in the solution is:
nmoles of NaOH = 3 * nmoles of H₃PO₄
We know that the volume of H₃PO₄ used in the titration is 1.17 L and its concentration is 2.19 M. Therefore, the number of moles of H₃PO₄ is:
nmoles of H₃PO₄ = concentration of H₃PO₄ * volume of H₃PO₄
= 2.19 mol/L * 1.17 L
= 2.56 mmol
Therefore, the number of moles of NaOH in the solution is:
nmoles of NaOH = 3 * nmoles of H₃PO₄
= 3 * 2.56 mmol
= 7.68 mmol
Finally, we can calculate the concentration of the NaOH solution by dividing the number of moles of NaOH by the volume of the solution:
concentration of NaOH = nmoles of NaOH / volume of NaOH solution
= 7.68 mmol / 0.785 L
= 0.00977 M
Therefore, the concentration of the NaOH solution is 0.00977 M.
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