Review 7th

Which of the following actions will increase the rate of dissolution of a solid solute into an aqueous solution?

• Stirring with a spoon

• Freezing the solute

• Decreasing the temperature

• Continuously adding more solute

Answer explanation

Stirring with a spoon increases the rate of dissolution by enhancing the interaction between the solute and solvent, allowing more solute to dissolve faster. Freezing, decreasing temperature, or adding more solute does not aid dissolution.

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-4

The image shows two different samples of the same compound, calcium carbonate. There are two beakers full of water. One sample is added to each beaker. Which of the following options correctly compares the rate of dissolution of the samples?

• The calcium carbonate stones will dissolve slowly since they have a lower surface area than the calcium carbonate powder.

• The calcium carbonate stones and calcium carbonate powder will dissolve at the same rate since they have the same surface area.

• The calcium carbonate stones will dissolve quickly since they have a greater surface area than the calcium carbonate powder.

• The calcium carbonate stones will dissolve slowly since they have a lower surface area than the calcium carbonate powder.

Answer explanation

The calcium carbonate stones have a lower surface area compared to the calcium carbonate powder, which means they will dissolve more slowly in water. This is why the correct choice is that the stones dissolve slowly.

You have a solution of saltwater. Which statement best describes what happens when you perform a dilution by adding water?

• The concentration of the solution will increase.

• The concentration of the solution does not change.

• The concentration of the solution will decrease.

• The amount of solute increases.

Answer explanation

When you dilute a saltwater solution by adding water, the total volume increases while the amount of salt (solute) remains the same. This results in a lower concentration of salt in the solution, making the correct choice "The concentration of the solution will decrease."

Zahara needs to make a CuSO4 solution as quickly as possible for class. What actions should she take to speed up the process of dissolving the CuSO4 in an aqueous solution?

Answer explanation

To speed up dissolving CuSO4, Zahara should stir the solution, increase the temperature, and use smaller crystals of CuSO4. These actions enhance solubility and increase the rate of dissolution.

Identify the solvent in this solution. Describe two different ways you could increase the concentration of the solution. Explain what action should not be taken because it would decrease the concentration of the solution. Be sure to use terms such as solute and solvent in your answer.

Answer explanation

The solvent is the substance that dissolves the solute. To increase concentration, you can add more solute or evaporate some solvent. Do not dilute the solution with more solvent, as this would decrease the concentration.

To increase the _________ of a solution, a person would dissolve more _________ into the _________. Which words best complete the sentence?

• dilution; solvent; solute

• dilution; solute; solvent

• concentration; solute; solvent

• concentration; solvent; solute

Answer explanation

To increase the concentration of a solution, one must dissolve more solute into the solvent. This correctly completes the sentence, as concentration refers to the amount of solute in a given volume of solvent.

A antacid tablet is a ______ that dissolves into the _______, water.

• solvent; solute

• solution; solute

• solute; solvent

• solvent; solution

Answer explanation

An antacid tablet acts as a solute that dissolves in water, which is the solvent. Therefore, the correct choice is 'solute; solvent'.

3. Erika is making a saltwater solution to remove ice from her driveway. She pours salt into a big bucket of water, but most of it sinks to the bottom.

What is the simplest way to get the salt to dissolve?

• 1. Stir the solution with a stick so the salt will dissolve.

• 1. Crush the granules of salt into a finer powder.

• 1. Heat the water so the salt dissolves and then cool it back down again.

• 1. Add ice to cool the salt even more so the salt dissolves.

Answer explanation

Heating the water increases its capacity to dissolve salt, making it the simplest method. Once the salt is dissolved, cooling the solution will not affect the dissolved salt, ensuring it remains in solution.

In a solution, what does the dissolving?

• solute

• solvent

• solution

• none of the above

Answer explanation

In a solution, the solvent is the substance that dissolves the solute. Therefore, the correct answer is 'solvent', as it is responsible for the dissolving process.

True or False.

A chemical change is reversible.

• true

• false

Answer explanation

A chemical change involves the formation of new substances, which typically cannot be reversed. Therefore, the statement that a chemical change is reversible is false.