Solubility

Solubility

Middle School

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Learning Objectives

• Define the key terms: solubility, solute, solvent, and solution.

• Differentiate between unsaturated, saturated, and supersaturated solutions.

• Explain how temperature and pressure affect the solubility of different substances.

• Identify factors that increase the rate of dissolving, like heating and stirring.

Key Vocabulary

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Solubility

The ability of a substance, the solute, to dissolve in a solvent to form a solution.

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Solute

The substance that is being dissolved in a solution, for example, sugar or salt.

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Solvent

The substance in a solution that does the dissolving, for example, water.

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Saturated Solution

A solution that contains the maximum amount of solute that can be dissolved at that temperature.

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Insoluble

A substance that cannot dissolve in a solvent is considered to be insoluble.

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What is Solubility?

• Solubility is how well a solute dissolves in a solvent to form a solution.

• A solution is a homogeneous mixture, meaning it looks the same throughout.

• A soluble substance like sugar dissolves, but an insoluble one like sand does not.

• Water is the "universal solvent" as it dissolves many different substances.

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Multiple Choice

In a solution made with sugar and water, which substance is the solute and which is the solvent?

• Both sugar and water are solutes.

• Sugar is the solvent, and water is the solute.

• Sugar is the solute, and water is the solvent.

• Both sugar and water are solvents.

Types of Solutions

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Unsaturated Solution

• This solution contains less solute than the maximum amount possible.

• You can continue to dissolve more solute into the solution.

• All of the solute is completely dissolved in the solvent.

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Saturated Solution

• Contains the maximum amount of solute that can be dissolved.

• If you add more solute, it will not dissolve anymore.

• Undissolved solute may settle at the bottom of the container.

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Supersaturated Solution

• This holds more solute than is normally possible at a temperature.

• These types of solutions are very unstable and can change easily.

• It is made by slowly cooling a hot, saturated solution.

Multiple Choice

You dissolve the maximum amount of salt possible in a glass of water at room temperature. What type of solution have you created?

• A supersaturated solution

• An insoluble solution

• A saturated solution

• An unsaturated solution

Factors Affecting Solubility

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Temperature

• For most solids, solubility increases when the temperature of the solvent increases.

• More sugar will dissolve in hot tea than it will in iced tea.

• For all gases, solubility decreases as the temperature of the solvent increases.

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Pressure

• Pressure mainly affects the solubility of gases in liquid solvents.

• As the pressure of a gas above a liquid increases, so does solubility.

• High pressure forces more gas particles to dissolve into the liquid.

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Rate of Dissolving

• You can make a solute dissolve faster by heating the solvent.

• Stirring or mixing the solution also increases the rate of dissolving.

• This changes the speed of dissolving, not how much can dissolve.

Multiple Choice

How does increasing the temperature of a liquid affect the solubility of a solid solute versus a gaseous solute?

• Increases for both solids and gases.

• Decreases for both solids and gases.

• Increases for solids, decreases for gases.

• Decreases for solids, increases for gases.

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Common Misconceptions About Solutions

Misconception	Correction
Any amount of a substance can dissolve in a liquid.	Solubility is limited; a solution can become saturated.
Dissolving is a chemical reaction.	Dissolving is a physical change, not a chemical one.
Heating always increases the solubility of a substance.	For gases, heating a liquid *decreases* their solubility.
Solutions are always a solid dissolved in a liquid.	Solutions can be gases, liquids, or solids. Air is a gaseous solution.

Multiple Choice

A can of soda fizzes when opened because the pressure is released. Why would a warm can of soda go 'flat' (lose its fizz) faster than a cold can?

• The solubility of the carbon dioxide gas is lower at higher temperatures.

• The water evaporates faster from the cold soda.

• The pressure increases more rapidly in the cold can.

• The sugar in the warm soda prevents the gas from escaping.

Multiple Choice

A student dissolves 35 grams of salt in 100 grams of water at 60°C. They cool the solution to 20°C, and no salt crystallizes. If the maximum solubility at 20°C is 30 grams, how can the solution at 20°C be classified?

• Unsaturated

• Supersaturated

• Saturated

• Insoluble

Multiple Choice

You are given two beakers, one with an unsaturated salt solution and one with a saturated salt solution, but you don't know which is which. What is the most effective way to identify the saturated solution?

• Heat both beakers; the saturated solution will start to boil first.

• Add a crystal of salt to each; it will dissolve only in the unsaturated solution.

• Taste both solutions; the saturated one will taste saltier.

• Shine a light through both; the saturated solution will be cloudier.

Multiple Choice

A factory needs to produce a large batch of a liquid product by dissolving a solid ingredient into a solvent as quickly and efficiently as possible. What combination of actions should they use?

• Apply high pressure and cool the solvent.

• Heat the solvent and let the solid sit at the bottom.

• Heat the solvent and stir the mixture vigorously.

• Cool the solvent and stir it slowly.

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Summary

• Solutions can be unsaturated, saturated, or supersaturated.

• The solubility of most solids increases with temperature.

• The solubility of gases decreases with temperature.

• The solubility of gases increases as pressure increases.

• Heating or stirring the mixture increases the rate of dissolving.

• Water is known as the "universal solvent".

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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