Question

What is the molarity of a solution composed of $5.85\mathrm{g}$ of potassium iodide, $\mathrm{KI}$, dissolved in enough water to make $0.125\mathrm{L}$ of solution?

Answer 1

Step 1: Given,

$$\begin{gathered} \mathrm{Mass}\mathrm{of}\mathrm{KI}=5.85\mathrm{g} \\ \mathrm{Volume}\mathrm{of}\mathrm{solution}=0.125\mathrm{L} \end{gathered}$$

Step 2: Formula used to calculate the molarity of a solution.

$\mathrm{Molarity}=\frac{\mathrm{m}}{\mathrm{M}\times \mathrm{V}}$

Where,

• $\mathrm{m}$ is mass of solute
• $\mathrm{M}$ is molar mass of solute
• $\mathrm{V}$ is volume of solution in liter

Step 3: To determine the molar mass of $\mathbf{KI}$.

$$\begin{gathered} \mathrm{Molar}\mathrm{mass}\mathrm{of}\mathrm{KI}=\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{K}+\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{I} \\ \mathrm{Molar}\mathrm{mass}\mathrm{of}\mathrm{KI}=39+126.9 \\ \mathrm{Molar}\mathrm{mass}\mathrm{of}\mathrm{KI}=165.9\mathrm{g}{\mathrm{mol}}^{-1} \end{gathered}$$

Step 4: To determine the molarity of a solution.

$$\begin{gathered} \mathrm{Molarity}=\frac{\mathrm{m}}{\mathrm{M}\times \mathrm{V}} \\ \mathrm{Molarity}=\frac{5.85\mathrm{g}}{165.9\mathrm{g}{\mathrm{mol}}^{-1}\times 0.125\mathrm{L}} \\ \mathrm{Molarity}=0.282\mathrm{mol}{\mathrm{L}}^{-1} \end{gathered}$$

Therefore, the molarity of a solution is $\mathbf{0}\mathbf{.}\mathbf{282}\mathbf{}\mathbf{mol}\mathbf{}{\mathbf{L}}^{\mathbf{-}\mathbf{1}}$.