Chapter 19, Problem 128A

Interpretation Introduction

Interpretation : The grams of potassium hydroxide are to be calculated.

Concept Introduction : A solution's concentration is an indicator of how much solute has been dissolved in a specific amount of solvent. The formula to calculate concentration is given as

  $\text{c}\text{=}\frac{\text{n}}{\text{V}}$

Here, $\text{n}$ is the number of moles and $\text{V}$ is the volume of the solution.

Answer to Problem 128A

The potassium hydroxide of $\text{15}\text{.26}\text{g}$ is diluted in $\text{400}\text{mL}$ solution.

Explanation of Solution

The volume of $\text{KOH}$ solution is $\text{400}\text{mL}$ or $\text{0}\text{.4}\text{L}$ .

The concentration of $\text{KOH}$ solution is $0.680\text{M}$ .

The molecular mass of $\text{KOH}$ is $\text{56}\text{.1}\text{g/mol}$ .

The formula of concentration is given as

  $\text{c}\text{=}\frac{\text{n}}{\text{V}}$

Here, $\text{n}$ is the number of moles and $\text{V}$ is the volume of the solution.

The number of moles is the product of molecular mass and mass of the solute.

The formula of concentration can be given as

  $\text{c}\text{=}\frac{\text{M}\times \text{m}}{\text{V}}$

To calculate the mass of the solute, substitute the values in above formula:

  $\begin{array}{c}\text{c}\text{=}\frac{\text{M}\times \text{m}}{\text{V}}\\ \text{m}\text{=}\text{c×M×V}\\ =0.68\text{mol/L}\times \text{56}\text{.1}\text{g/mol}\times \text{0}\text{.4}\text{L}\\ \text{=15}\text{.26}\text{g}\end{array}$

About $\text{15}\text{.26}\text{g}$ is diluted in $\text{400}\text{ml}$ in order to get the prepare $0.680\text{M}$ of $\text{KOH}$ .