Unit 2: Properties of Solutions (7.6D)

A solution is made by dissolving 10 grams of salt in 100 mL of water. If the solution is diluted by adding 50 mL of water, what is the new concentration of the solution in grams per mL?

• 0.1 g/mL

• 0.067 g/mL

• 0.15 g/mL

• 0.2 g/mL

Answer explanation

Initially, the concentration is 10 g / 100 mL = 0.1 g/mL. After adding 50 mL of water, the total volume is 150 mL. The concentration becomes 10 g / 150 mL = 0.067 g/mL, which is the correct answer.

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DOK Level 3: Strategic Thinking

TEKS.SCI.7.6D

Which of the following factors does NOT affect the rate of dissolution of a solute in a solvent?

• Temperature

• Surface area of the solute

• Color of the solute

• Stirring

Answer explanation

The color of the solute does not influence how quickly it dissolves in a solvent. Factors like temperature, surface area, and stirring directly impact the rate of dissolution.

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A scientist needs to prepare 500 mL of a 0.2 M solution from a 1 M stock solution. How much of the stock solution should be used?

• 100 mL

• 200 mL

• 50 mL

• 250 mL

Answer explanation

To prepare a 0.2 M solution from a 1 M stock, use the dilution formula: C1V1 = C2V2. Here, C1 = 1 M, C2 = 0.2 M, and V2 = 500 mL. Solving for V1 gives V1 = (0.2 M * 500 mL) / 1 M = 100 mL.

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In a laboratory experiment, a student observes that sugar dissolves faster in hot water than in cold water. Which of the following best explains this observation?

• Hot water has a higher density.

• Sugar molecules are smaller in hot water.

• The increased temperature increases the kinetic energy of water molecules.

• Hot water has a different pH level.

Answer explanation

The increased temperature raises the kinetic energy of water molecules, allowing them to collide with sugar molecules more frequently and effectively, leading to faster dissolution in hot water.

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DOK Level 3: Strategic Thinking

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A graph shows the concentration of a solute in a solution over time. If the graph shows a steady decrease in concentration, what process is most likely occurring?

• Evaporation

• Dilution

• Precipitation

• Saturation

Answer explanation

The steady decrease in solute concentration indicates that the solution is being diluted, likely by the addition of more solvent, which reduces the concentration of the solute over time.

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Which of the following real-world applications involves the concept of dilution?

• Mixing paint colors

• Preparing a saline solution for medical use

• Baking a cake

• Growing crystals

Answer explanation

Dilution is crucial in preparing a saline solution for medical use, as it involves mixing a concentrated salt solution with water to achieve the desired concentration for safe administration.

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If a solution is described as being "saturated," what does this mean in terms of solute and solvent?

• The solvent can dissolve more solute.

• The solute has completely evaporated.

• The solution contains the maximum amount of solute that can dissolve at that temperature.

• The solute and solvent are in equal proportions.

Answer explanation

A saturated solution means it contains the maximum amount of solute that can dissolve in the solvent at a specific temperature. This indicates that no more solute can be added without it precipitating out.

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A student is tasked with increasing the concentration of a solution. Which of the following actions would achieve this?

• Adding more solvent

• Adding more solute

• Heating the solution

• Cooling the solution

Answer explanation

To increase the concentration of a solution, you should add more solute. This increases the amount of dissolved substance relative to the solvent, making the solution more concentrated. Adding solvent would dilute the solution.

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How does increasing the surface area of a solute affect its rate of dissolution in a solvent?

• It decreases the rate of dissolution.

• It has no effect on the rate of dissolution.

• It increases the rate of dissolution.

• It changes the solute's chemical properties.

Answer explanation

Increasing the surface area of a solute allows more solute particles to interact with the solvent, leading to a faster rate of dissolution. Therefore, it increases the rate of dissolution.

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Match the following

• Concentrated Solution

• 
• Diluted Solution

• 
• Saturated Solution

• 

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NGSS.MS-PS1-2

NGSS.MS-PS1-5