Chapter 15, Problem 9STP

Interpretation Introduction

Interpretation:

The volume of given ammonium hydroxide solution is to be calculated when it is neutralized by acid.

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 9STP

A

Explanation of Solution

Given data:

  $\begin{array}{l}{V}_{HCl}=45mL\\ MolarityofHCl=0.4\text{}M\\ MolarityofNaOH=0.5\text{}M\end{array}$

  $\begin{array}{c}{n}_{HCl}=Molarity\times volumeinliters\\ =0.4\times \frac{45}{1000}\\ =18\times {10}^{-3}mol\end{array}$

When hydrochloric acid reacts with ammonium hydroxide reaction is given by:

  $HCl+NaOH\to NaCl+H_{2}O$

Thus one mol acid reacts with one mol base.

This implies,

  $n_{NaOH}=18\times {10}^{-3}mol$

  $\begin{array}{c}VolumeofNaOHsolution=\frac{18\times {10}^{-3}mol}{0.5}\\ =36\times {10}^{-3}L\\ =36mL\end{array}$

Conclusion

Mathematical calculations shows option A is correct and remaining options are wrong.