Chapter 19, Problem 7STP

Interpretation Introduction

Interpretation : The molarity of hydrochloric acid is to be calculated.

Concept Introduction : Salt and water are created when bases and acids react.

A strong acid and strong base react completely to form a neutral solution. A neutralization reaction is a name for this kind of reaction.

The formula of molarity is given as

  $\text{molarity}\text{=}\frac{\text{mol}\text{of}\text{solute}}{\text{L}\text{of}\text{solution}}$

Answer to Problem 7STP

Correct answer: Option (B)

The molarity of HCl solution is $0.496\text{M}$ .

Explanation of Solution

Reason for correct option:

The volume of $\text{HCl}$ is $\text{25}\text{.0}\text{mL}$ .

The concentration of $\text{NaOH}$ is $\text{0}\text{.80}\text{M}$ .

The volume of $\text{NaOH}$ is $15.5\text{mL}$ .

The reaction between sodium hydroxide and hydrochloric acid is given as

  $\text{NaOH}\left(aq\right)\text{+}\text{HCl}\left(aq\right)\to \text{NaCl}\left(aq\right)\text{+}{\text{H}}_{\text{2}}\text{O}\left(l\right)$

The above reaction is the balanced reaction.

The mole ratio is $1:1$ for the reaction between $\text{NaOH}$ and $\text{HCl}$ .

The moles of sodium hydroxide are calculated as follows:

  $\begin{array}{c}\text{Moles of NaOH}\text{= 0}\text{.0155}\cancel{\text{L NaOH}}\times \frac{0.8\text{mol}\text{NaOH}}{1\cancel{\text{L}\text{NaOH}}}\\ =0.0124\text{mol}\text{NaOH}\end{array}$

The moles of hydrochloric acid are calculated as follows:

  $\begin{array}{c}\text{Moles of HCl}\text{= 0}\text{.0124}\cancel{\text{mol NaOH}}\times \frac{1\text{mol}\text{HCl}}{1\cancel{\text{mol}\text{NaOH}}}\\ =0.0124\text{mol}\text{HCl}\end{array}$

The molarity of $\text{HCl}$ is given as

  $\begin{array}{c}\text{molarity}\text{=}\frac{\text{mol}\text{of}\text{solute}}{\text{L}\text{of}\text{solution}}\\ =\frac{0.0124\text{mol}}{0.025\text{L}}\\ =0.496\text{M}\end{array}$

So, option (B) is the correct answer.

Conclusion

Reasons for incorrect options:

Option (A), (C), (D): All these options are irrelevant because it does not gives the correct molarity of HCl solution.