Q. 9.114 - An Introduction to General, Organic, and Biological Chemistry

Question

In a laboratory experiment, a $15.0‐ \mathrm{mL}$ sample of $\mathrm{KCl}$ the solution is poured into an evaporating dish a mass of $24.10 \mathrm{g}$. The combined mass of the evaporating dish and $\mathrm{KCl}$solution is $41.50 \mathrm{g}$. After heating, the evaporating dish and dry $\mathrm{KCl}$ have a combined mass of $28.28 \mathrm{g}. (9.4)$

a. What is the mass percent $\left(\mathrm{m}/\mathrm{m}\right)$ of the $\mathrm{KCl}$ solution?

b. What is the molarity $\left(\mathrm{M}\right)$ of the $\mathrm{KCl}$ solution?

c. If water is added to $10.0 \mathrm{mL}$ of the initial $\mathrm{KCl}$ solution to give a final volume of $60.0 \mathrm{mL}$, what is the molarity of the diluted $\mathrm{KCl}$ solution?

Step-by-Step Solution

Answer

a. The mass percent $(\mathrm{m}/\mathrm{m})$ of the $\mathrm{KCl}$solution is $24 \%$.

b. The molarity $\left(\mathrm{M}\right)$ of $\mathrm{KCl}$ the solution is $1.61 \mathrm{M}$.

c. the molarity of the diluted $60.0 \mathrm{mL}$ solution is  $0.27 \mathrm{M}$.

Part (a) Step 1: Given Information

Amount of KCL = $15ml$

Mass of evaporating dish = $24.10g$

Combined mass = $41.50g$ and after heating the mass = $28.28g$

Finding the mass percent  of the KCL solution

Part (a) Step 2: Explanation

Now,

Calculating the mass percent,

$\left(\mathrm{m}/\mathrm{m}\right)=\frac{28.28 \mathrm{g}-24.10 \mathrm{g}}{41.50 \mathrm{g}-24.10 \mathrm{g}}=0.24$

the mass percent is $0.24\%$.

Part (b) Step 1: Given Information

Amount of KCL = $15ml$

Mass of evaporating dish = $24.10g$

Combined mass =$41.50g$  and after heating the mass = $28.28g$

finding the molarity $\left(\mathrm{M}\right)$ of the $\mathrm{KCl}$ solution.

Part (b) Step 2: Explanation

Here,

Calculating the molarity,

$\mathrm{c}=\frac{24.10 \mathrm{g}}{15 \mathrm{mL}}=1.61 \mathrm{M}$

the molarity is $1.61 \mathrm{M}$.

Part (c) Step 1: Given Information

Amount of KCL = $15ml$

Mass of evaporating dish = $24.10g$

Combined mass = $41.50g$ and after heating the mass = $28.28g$

finding the molarity of the diluted $60.0 \mathrm{mL}$ solution.

Part (c) Step 2: Explanation

Now,

Calculating the molarity of the diluted $60.0 \mathrm{mL}$, 

${\mathrm{c}}_2=\frac{{\mathrm{c}}_1\times {\mathrm{V}}_1}{{\mathrm{V}}_2}=\frac{1.61 \mathrm{M} \times 10 \mathrm{mL}}{60 \mathrm{mL}}=0.27 \mathrm{M}$