Chemistry worksheet on solution concentration calculations.

Problem 1: Percent Concentration (m/m)

Question: If you dissolve 8.56 grams of sodium chloride in 25.09 grams of water, calculate the percent (m/m) of sodium chloride.

#### Solution:
The formula for mass percent concentration (m/m) is:

\[
\text{Percent (m/m)} = \left( \frac{\text{Mass of solute}}{\text{Total mass of solution}} \right) \times 100
\]

1. Identify the given values:
- Mass of sodium chloride (solute) = 8.56 g
- Mass of water (solvent) = 25.09 g

2. Calculate the total mass of the solution:
\[
\text{Total mass of solution} = \text{Mass of solute} + \text{Mass of solvent}
\]
\[
\text{Total mass of solution} = 8.56 \, \text{g} + 25.09 \, \text{g} = 33.65 \, \text{g}
\]

3. Substitute the values into the formula:
\[
\text{Percent (m/m)} = \left( \frac{8.56 \, \text{g}}{33.65 \, \text{g}} \right) \times 100
\]

4. Perform the calculation:
\[
\text{Percent (m/m)} = \left( \frac{8.56}{33.65} \right) \times 100 \approx 25.4\%
\]

#### Final Answer:
\[
\boxed{25.4\%}
\]

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Problem 2: Molarity Calculation

Question: Calculate the molarity of a solution that contains 18.9 grams of sodium hydroxide in 3.67 L of solution.

#### Solution:
The formula for molarity (\(M\)) is:

\[
M = \frac{\text{moles of solute}}{\text{volume of solution (in liters)}}
\]

1. Identify the given values:
- Mass of sodium hydroxide (NaOH) = 18.9 g
- Volume of solution = 3.67 L

2. Calculate the molar mass of NaOH:
- Sodium (Na): \(22.99 \, \text{g/mol}\)
- Oxygen (O): \(16.00 \, \text{g/mol}\)
- Hydrogen (H): \(1.01 \, \text{g/mol}\)
\[
\text{Molar mass of NaOH} = 22.99 + 16.00 + 1.01 = 40.00 \, \text{g/mol}
\]

3. Calculate the moles of NaOH:
\[
\text{Moles of NaOH} = \frac{\text{Mass of NaOH}}{\text{Molar mass of NaOH}}
\]
\[
\text{Moles of NaOH} = \frac{18.9 \, \text{g}}{40.00 \, \text{g/mol}} = 0.4725 \, \text{mol}
\]

4. Calculate the molarity:
\[
M = \frac{\text{Moles of solute}}{\text{Volume of solution (in liters)}}
\]
\[
M = \frac{0.4725 \, \text{mol}}{3.67 \, \text{L}} \approx 0.13 \, \text{mol/L}
\]

#### Final Answer:
\[
\boxed{0.13 \, \text{mol/L}}
\]

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Problem 3: Moles from Molarity

Question: How many moles of potassium hydroxide are in 4.82 mL of a 0.050 M solution of potassium hydroxide?

#### Solution:
The formula to calculate moles from molarity is:

\[
\text{Moles of solute} = M \times V
\]

where:
- \(M\) is the molarity of the solution.
- \(V\) is the volume of the solution in liters.

1. Identify the given values:
- Molarity (\(M\)) = 0.050 mol/L
- Volume (\(V\)) = 4.82 mL

2. Convert the volume from mL to L:
\[
V = 4.82 \, \text{mL} \times \frac{1 \, \text{L}}{1000 \, \text{mL}} = 0.00482 \, \text{L}
\]

3. Calculate the moles of potassium hydroxide:
\[
\text{Moles of solute} = M \times V
\]
\[
\text{Moles of solute} = 0.050 \, \text{mol/L} \times 0.00482 \, \text{L} = 0.000241 \, \text{mol}
\]

#### Final Answer:
\[
\boxed{0.000241 \, \text{mol}}
\]

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Summary of Answers:

1. Percent (m/m) of sodium chloride: \(\boxed{25.4\%}\)
2. Molarity of sodium hydroxide solution: \(\boxed{0.13 \, \text{mol/L}}\)
3. Moles of potassium hydroxide: \(\boxed{0.000241 \, \text{mol}}\)