Question

a chemistry student weighs out 0.232 g of phosphoric acid (h₃po₄), a triprotic acid, into a 250. ml volumetric flask and dilutes to the mark with distilled water. he plans to titrate the acid with 0.1700 m naoh solution. calculate the volume of naoh solution the student will need to add to reach the final equivalence point. round your answer to 3 significant digits. ml

Explanation:

Step1: Calculate the moles of \(H_3PO_4\)

The molar mass of \(H_3PO_4\) is \(M=(3\times1 + 31+4\times16)\space g/mol=98\space g/mol\).
Using the formula \(n=\frac{m}{M}\), where \(m = 0.232\space g\) and \(M = 98\space g/mol\), we have \(n_{H_3PO_4}=\frac{0.232\space g}{98\space g/mol}\approx0.00237\space mol\).

Step2: Determine the mole - ratio between \(H_3PO_4\) and \(NaOH\)

The balanced chemical equation for the reaction between \(H_3PO_4\) (a tri - protic acid) and \(NaOH\) is \(H_3PO_4+3NaOH = Na_3PO_4 + 3H_2O\). The mole ratio \(n_{H_3PO_4}:n_{NaOH}=1:3\). So \(n_{NaOH}=3n_{H_3PO_4}\).
Substituting \(n_{H_3PO_4}=0.00237\space mol\), we get \(n_{NaOH}=3\times0.00237\space mol = 0.00711\space mol\).

Step3: Calculate the volume of \(NaOH\) solution

Using the formula \(V=\frac{n}{C}\), where \(n = n_{NaOH}=0.00711\space mol\) and \(C = 0.1700\space M\).
\(V=\frac{0.00711\space mol}{0.1700\space mol/L}\approx0.0418\space L\).
Since \(1\space L = 1000\space mL\), \(V = 0.0418\times1000\space mL=41.8\space mL\).

Answer:

\(41.8\space mL\)