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E3.3 · Explain temperature and pressure effects on solubility

Learn to explain temperature and pressure effects on solubility through clear examples and targeted practice.

Ontario Grade 11 Chemistry

Solutions and Solubility

Ontario Grade 11 Chemistry — study topic E3.3

Think about a cold, sealed bottle of a carbonated drink. When you open it, gas bubbles appear and rise. The drink contains dissolved gas, and opening the bottle lowers the pressure above the liquid. This example shows that conditions can affect how much of a substance stays dissolved. To explain the effect, first recall what dissolving means: particles of a solute spread through a solvent to make a solution. Solubility describes the maximum amount of solute that can dissolve in a given amount of solvent under stated conditions. Temperature and, for gases, pressure are important conditions. Their effects depend on whether the solute is a solid or a gas.

What you will learn

Define solubility and identify the conditions that affect it.
Explain how temperature usually affects the solubility of solid substances and gases in water.
Explain how pressure affects the solubility of a gas in a liquid.
Use particle-level reasoning to explain these patterns and recognize their limits.

1. A useful starting point: solutions and solubility

A solution is a uniform mixture. Its solvent is the substance that does the dissolving, and its solute is the substance being dissolved. In salt water, water is the solvent and salt is the solute. The dissolved particles are spread among the water particles, so they are not usually visible as separate grains.

Solubility is not the same as the amount that happens to be dissolved in a sample. It is the maximum amount that can dissolve in a specified amount of solvent at a particular temperature and pressure. A solution holding that maximum is called saturated. If less solute is dissolved than the maximum, the solution is unsaturated.

For example, a spoonful of a solid may dissolve in water, while extra solid remains at the bottom. The remaining solid is evidence that the solution has reached its capacity under those conditions. Changing the temperature can change that capacity. For a gas dissolved in a liquid, changing the pressure above the liquid can also change it.

Solubility refers to a maximum amount under stated conditions.
Temperature and pressure must be considered when comparing solubility.
The effect of a condition depends on whether the solute is a solid or a gas.

2. Temperature and solid solutes

In many familiar cases, more solid solute can dissolve in a liquid when the temperature is higher. For example, a hot drink can often dissolve more sugar than the same amount of cooler water. This is a general pattern, not a rule for every solid. Some solids show a small change, and a few become less soluble as temperature rises.

At the particle level, particles in warmer water move more rapidly. This motion helps water particles separate and surround particles from the solid. For many solids, the warmer conditions also make it possible for more solute particles to be present in the solution before the solution reaches its maximum. The key observation is the change in the maximum amount that dissolves, not simply how quickly the solid disappears.

A faster dissolving rate and a greater solubility are different ideas. Stirring or crushing a solid can make it dissolve faster, but those changes do not, by themselves, mean that more solid can dissolve in total. When explaining temperature and solubility, compare the maximum dissolved amount under the different temperatures.

Pressure has little effect on the solubility of solids in liquids in ordinary classroom situations. Solid and liquid particles are already close together, so changing the pressure above the liquid does not substantially change how much solid dissolves. The strong pressure effect discussed in this lesson applies to gases dissolved in liquids.

For many solid solutes, solubility increases as temperature rises.
This temperature pattern has exceptions, so avoid saying it is true for every solid.
A change in dissolving speed is not necessarily a change in solubility.
Pressure has little effect on the solubility of a solid in a liquid.

3. Temperature and pressure effects on gases

A gas dissolved in a liquid often behaves in the opposite way to a solid. As the liquid gets warmer, the solubility of most gases in it decreases. A warm carbonated drink tends to lose dissolved gas more readily than a cold one. In the particle model, gas particles move more rapidly at higher temperature, so they are more likely to leave the liquid and spread into the space above it.

Pressure has a clear effect on the solubility of a gas in a liquid. Increasing the pressure of the gas above a liquid generally allows more of that gas to dissolve. The gas particles are packed more closely above the liquid and have more opportunities to enter it. Lowering the pressure has the opposite effect: dissolved gas can leave the liquid more readily.

A sealed carbonated drink is kept under pressure, which helps maintain dissolved carbon dioxide. Opening the container lowers the pressure above the drink. Some carbon dioxide then leaves the liquid as bubbles. The bubbles are a visible sign of gas escaping; they do not mean that the gas has changed into a different substance.

These patterns are useful general rules for gases dissolved in liquids: higher pressure usually means greater gas solubility, while higher temperature usually means lower gas solubility. The rules describe trends. They do not give an exact amount without additional information about the substance and conditions.

For most gases dissolved in liquids, increasing temperature lowers solubility.
Increasing the pressure of a gas above a liquid generally increases its solubility.
Lower pressure lets dissolved gas escape more readily.
Bubbles from an opened carbonated drink are observable evidence of gas leaving the liquid.

4. Compare like conditions and explain the trend

A clear comparison changes one condition at a time. To describe a temperature effect, compare the same solute and solvent at different temperatures while keeping other conditions alike. To describe a pressure effect on a gas, compare the same gas and liquid at different pressures. This makes it easier to identify which change is linked to the solubility difference.

Use the substance type to choose the expected trend. For a solid in a liquid, higher temperature usually allows more to dissolve, though exceptions exist; pressure usually has little effect. For a gas in a liquid, higher temperature usually means less can remain dissolved, while higher pressure usually means more can dissolve.

Solubility can be reported with units, such as grams of solute per 100 grams of solvent. If a question provides a solubility value, keep its units attached while comparing values. Do not assume a numerical relationship that was not provided. The trends in this lesson are qualitative: they show the usual direction of change, not a formula for calculating an exact solubility.

Identify whether the solute is a solid or a gas before predicting a temperature effect.
State the condition being changed and the direction of the solubility change.
Use units when a numerical solubility value is supplied; do not invent a value from a qualitative trend.

Usual solubility trends in a liquid

Solute type	Higher temperature	Higher pressure
Solid	Usually increases solubility; exceptions occur	Little effect
Gas	Usually decreases solubility	Usually increases solubility

Worked example

Explaining a change in a carbonated drink

A sealed carbonated drink is cold. It is opened and left to warm. Explain how the pressure and temperature changes affect the solubility of carbon dioxide in the drink.

Identify the solute
Carbon dioxide is the gas solute, and the liquid drink is the solvent. The gas rules apply.
Consider opening the container
Opening the container lowers the pressure above the liquid. At lower pressure, less gas tends to remain dissolved, so carbon dioxide leaves the drink as bubbles.
Consider warming the drink
For most gases dissolved in liquids, raising the temperature lowers solubility. As the drink warms, less carbon dioxide can remain dissolved under the new conditions.
Combine the effects
Both changes favour carbon dioxide leaving the liquid: the pressure decreases and the temperature increases. The visible bubbles are consistent with gas escaping.

Answer: Opening the drink lowers pressure, and warming it raises temperature. Both changes lower the amount of carbon dioxide that tends to remain dissolved, so gas escapes as bubbles.

Check: The prediction follows the gas-in-liquid trends: lower pressure and higher temperature both reduce gas solubility.

Common mistakes and how to avoid them

Saying that heating always increases solubility.

Correction: Heating usually increases the solubility of many solids, but usually decreases the solubility of gases. Some solids are exceptions.

Treating faster dissolving as proof that more solute can dissolve.

Correction: Dissolving speed describes how quickly a solute dissolves. Solubility describes the maximum amount that can dissolve under specified conditions.

Claiming that pressure strongly changes the solubility of every substance.

Correction: Pressure has a noticeable effect on gases dissolved in liquids. It usually has little effect on solid solutes in liquids.

Saying that opening a carbonated drink increases gas solubility.

Correction: Opening lowers the pressure above the drink. Lower pressure means less gas tends to stay dissolved, so bubbles can form.

Lesson summary

Solubility is the maximum amount of solute that dissolves in a specified amount of solvent under stated conditions.
For many solids in liquids, higher temperature usually increases solubility, but exceptions occur.
For most gases in liquids, higher temperature usually decreases solubility.
Higher pressure usually increases the solubility of a gas in a liquid. Lower pressure encourages dissolved gas to escape.
Pressure usually has little effect on the solubility of solids in liquids.

Check your understanding

Question 1

A gas is dissolved in a liquid. What usually happens to its solubility when the pressure above the liquid increases?

It increases.
It decreases.
It stays exactly the same in every case.
correctIndex

Show answer and explanation

It increases.

Higher pressure above a liquid generally allows more gas to dissolve.

Question 2

What is the usual effect of warming a liquid that contains a dissolved gas?

The gas solubility usually increases.
The gas solubility usually decreases.
The gas changes into a solid.
correctIndex

Show answer and explanation

The gas solubility usually decreases.

For most gases dissolved in liquids, higher temperature lowers solubility.

Question 3

Which statement best describes many solid solutes in water?

Higher temperature usually allows more to dissolve, though exceptions occur.
Higher pressure always causes much more to dissolve.
Higher temperature always makes the solid less soluble.
correctIndex

Show answer and explanation

Higher temperature usually allows more to dissolve, though exceptions occur.

Many solids become more soluble as temperature rises, but this is not true of every solid.

Key terms

Solution: A uniform mixture in which one or more solutes are spread through a solvent.
Solute: The substance that is dissolved in a solution.
Solvent: The substance that dissolves the solute.
Solubility: The maximum amount of solute that can dissolve in a stated amount of solvent under specified conditions.
Saturated solution: A solution that contains the maximum amount of dissolved solute possible under its conditions.
Particle model: A way to explain matter by describing it as tiny particles and considering how they move and interact.

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Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 11 Chemistry (SCH3U), expectation E3.3. It is a study resource, not an official curriculum publication.

Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.

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