Chapter 16, Problem 63A

Interpretation Introduction

Interpretation:

The Molar mass of acid solution is to be calculated when it is neutralized by base.

Concept introduction:

Molarity is number of moles of solute present per liter of solution.

When acid and base are mixed, they neutralize each other. So their molar concentrations can be calculated by applying mole concept.

Answer to Problem 63A

  $Molarmassofacid=37.3g/mol$

Explanation of Solution

Given data:

  $\begin{array}{l}{V}_{NaOH}=29.7mL\\ massofHA=0.500g\\ MassofsolutionofHA(approximately)=100mL\\ MolarityofNaOH=0.450M\end{array}$

  $\begin{array}{c}{n}_{NaOH}=Molarity\times volumeinliters\\ =0.45\times \frac{29.7}{1000}\\ =1.34\times {10}^{-2}mol\end{array}$

The given reaction is:

  $HA+NaOH\to NaA+H_{2}O$

Thus one mol acid reacts with one mol base.

This impies,

  $n_{HA}=1.34\times {10}^{-2}mol$

  $\begin{array}{c}molarmass=\frac{givenmass}{numberofmoles}\\ molarmass=\frac{0.500}{1.34\times {10}^{-2}}\\ =37.3g/mol\end{array}$

Conclusion

  $Molarmassofacid=37.3g/mol$ .