Concentration Worksheet 1 - Free Printable

Concentration Worksheet Solutions

#### 1) Explain why chemical compounds tend to dissolve more quickly in hot solvent than in cold solvent.

Solution:
Chemical compounds tend to dissolve more quickly in hot solvents compared to cold solvents due to the following reasons:

- Increased Kinetic Energy: When a solvent is heated, the molecules gain kinetic energy. This increased motion allows solute particles to move more rapidly and collide more frequently with the solvent molecules, facilitating faster dissolution.

- Enhanced Solvent Mobility: The increased kinetic energy of the solvent molecules also leads to greater mobility, allowing them to surround and separate solute particles more efficiently.

- Weakened Intermolecular Forces: Heating can weaken the intermolecular forces (e.g., hydrogen bonds, van der Waals forces) between solute particles, making it easier for the solvent to break these interactions and dissolve the solute.

In summary, heat accelerates the dissolution process by increasing molecular motion and reducing the resistance to solvation.

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#### 2) Give an example of two liquids that are immiscible.

Solution:
Two liquids are considered immiscible if they do not mix with each other in any proportion. A common example is oil and water. Oil (e.g., vegetable oil or mineral oil) and water are immiscible because oil is nonpolar, while water is polar. Polar and nonpolar substances generally do not mix due to differences in their intermolecular forces.

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#### 3) How can you make a saturated solution from a supersaturated solution?

Solution:
A supersaturated solution contains more dissolved solute than a saturated solution at a given temperature. To convert a supersaturated solution into a saturated solution, follow these steps:

1. Cool the Solution: Supersaturation is often achieved by dissolving a solute in a hot solvent and then cooling it slowly. To make the solution saturated, allow the solution to cool further until the excess solute begins to crystallize out. At this point, the solution will be saturated.

2. Add a Seed Crystal: Alternatively, add a small crystal of the solute (a "seed crystal") to the supersaturated solution. This provides a surface for the excess solute to crystallize onto, causing the solution to become saturated.

By either cooling the solution or adding a seed crystal, the excess solute will precipitate, leaving behind a saturated solution.

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#### 4) How can you make a supersaturated solution from a saturated solution?

Solution:
To convert a saturated solution into a supersaturated solution, follow these steps:

1. Heat the Solution: Heat the saturated solution to increase its temperature. As the temperature rises, the solubility of most solutes increases, allowing more solute to dissolve in the solvent.

2. Stir Vigorously: While heating, stir the solution vigorously to ensure that additional solute dissolves completely.

3. Cool Slowly: After heating, allow the solution to cool slowly. During slow cooling, the solute remains dissolved even though the solubility decreases with lower temperatures, resulting in a supersaturated solution.

By heating and then slowly cooling the saturated solution, you can create a supersaturated solution where the solute concentration exceeds the saturation limit at the final temperature.

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#### 5) How can you make an unsaturated solution from a saturated solution?

Solution:
An unsaturated solution contains less solute than the maximum amount that can dissolve at a given temperature. To convert a saturated solution into an unsaturated solution, follow these steps:

1. Add More Solvent: Add more solvent (e.g., water) to the saturated solution. This dilutes the solution, reducing the concentration of the solute below the saturation limit.

2. Increase Temperature: Increase the temperature of the saturated solution. As the temperature rises, the solubility of the solute increases, allowing the solution to hold more solute without becoming saturated. However, since no additional solute is added, the solution becomes unsaturated.

By either adding more solvent or increasing the temperature, the solution will become unsaturated.

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#### 6) What is the molarity of a solution made when you dilute 35 grams of sodium carbonate to a volume of 3,400 mL?

Solution:
To calculate the molarity of the solution, we use the formula:

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

Step 1: Calculate the moles of sodium carbonate.

The molar mass of sodium carbonate (\(\text{Na}_2\text{CO}_3\)) is calculated as follows:
- Sodium (\(\text{Na}\)): \(23.0 \, \text{g/mol} \times 2 = 46.0 \, \text{g/mol}\)
- Carbon (\(\text{C}\)): \(12.0 \, \text{g/mol}\)
- Oxygen (\(\text{O}\)): \(16.0 \, \text{g/mol} \times 3 = 48.0 \, \text{g/mol}\)

\[
\text{Molar mass of } \text{Na}_2\text{CO}_3 = 46.0 + 12.0 + 48.0 = 106.0 \, \text{g/mol}
\]

Now, calculate the moles of sodium carbonate:
\[
\text{Moles of } \text{Na}_2\text{CO}_3 = \frac{\text{mass}}{\text{molar mass}} = \frac{35 \, \text{g}}{106.0 \, \text{g/mol}} \approx 0.3302 \, \text{mol}
\]

Step 2: Convert the volume of the solution to liters.

\[
\text{Volume} = 3,400 \, \text{mL} = 3.400 \, \text{L}
\]

Step 3: Calculate the molarity.

\[
\text{Molarity} = \frac{\text{moles of solute}}{\text{liters of solution}} = \frac{0.3302 \, \text{mol}}{3.400 \, \text{L}} \approx 0.0971 \, \text{M}
\]

Thus, the molarity of the solution is:

\[
\boxed{0.097 \, \text{M}}
\]

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#### 7) Explain how you would make 450 mL of a 0.25 M calcium chloride solution.

Solution:
To prepare 450 mL of a 0.25 M calcium chloride (\(\text{CaCl}_2\)) solution, follow these steps:

1. Calculate the moles of calcium chloride needed.

The formula for molarity is:
\[
\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}
\]

Rearrange to solve for moles:
\[
\text{Moles of solute} = \text{Molarity} \times \text{liters of solution}
\]

Convert the volume to liters:
\[
450 \, \text{mL} = 0.450 \, \text{L}
\]

Now calculate the moles:
\[
\text{Moles of } \text{CaCl}_2 = 0.25 \, \text{M} \times 0.450 \, \text{L} = 0.1125 \, \text{mol}
\]

2. Calculate the mass of calcium chloride needed.

The molar mass of calcium chloride (\(\text{CaCl}_2\)) is calculated as follows:
- Calcium (\(\text{Ca}\)): \(40.1 \, \text{g/mol}\)
- Chlorine (\(\text{Cl}\)): \(35.5 \, \text{g/mol} \times 2 = 71.0 \, \text{g/mol}\)

\[
\text{Molar mass of } \text{CaCl}_2 = 40.1 + 71.0 = 111.1 \, \text{g/mol}
\]

Now, calculate the mass:
\[
\text{Mass of } \text{CaCl}_2 = \text{moles} \times \text{molar mass} = 0.1125 \, \text{mol} \times 111.1 \, \text{g/mol} \approx 12.50 \, \text{g}
\]

3. Prepare the solution.

- Weigh out 12.50 g of calcium chloride.
- Dissolve the calcium chloride in a small amount of distilled water in a volumetric flask.
- Once the solid is completely dissolved, add more distilled water to the flask until the total volume reaches 450 mL.
- Mix thoroughly to ensure the solution is homogeneous.

By following these steps, you will have prepared 450 mL of a 0.25 M calcium chloride solution.

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Final Answers:

1. Chemical compounds dissolve more quickly in hot solvents due to increased kinetic energy, enhanced solvent mobility, and weakened intermolecular forces.
2. Oil and water are immiscible liquids.
3. Cool the supersaturated solution or add a seed crystal to make it saturated.
4. Heat the saturated solution and cool it slowly to make it supersaturated.
5. Add more solvent or increase the temperature to make the solution unsaturated.
6. The molarity is \(\boxed{0.097 \, \text{M}}\).
7. Weigh 12.50 g of calcium chloride, dissolve it in water, and dilute to 450 mL.