Solubility Curves

Solubility Curves

Middle School

​

Learning Objectives

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

• Explain the relationship between temperature and the solubility of solids.

• Interpret solubility curves to find the amount of solute that dissolves.

Key Vocabulary

​

Solution

A homogeneous mixture where substances are evenly mixed together, forming a single phase.

​

Solute

The substance in a solution that is being dissolved by another substance, the solvent.

​

Solvent

The substance in a solution that does the dissolving of another substance, the solute.

​

Solubility

The maximum amount of a substance that can dissolve in a solvent at a specific temperature.

​

​

What is a Solution?

Solute

• A solution is a homogeneous mixture where substances are evenly mixed together.

• The solute is the substance that gets dissolved into the other substance.

• For example, the flavor mix is the solute when you are making Kool-Aid.

Solvent

• A solution is made of two parts: a solute and the solvent.

• The solvent is the substance that does the dissolving of the other substance.

• For example, the water is the solvent when you are making Kool-Aid.

Multiple Choice

When you make hot chocolate, the chocolate powder is the what?

• Solute

• Solvent

• Solution

• Mixture

​

​

Temperature and Solubility

Higher Temperature

• When a solvent gets warmer, its particles gain energy and move much faster.

• This increased movement allows more solid solute particles to dissolve in the solvent.

• As a result, the solubility of the solid solute increases with higher temperatures.

Lower Temperature

• When a solvent gets cooler, its particles lose energy and start to slow down.

• This reduced movement means fewer solid solute particles can be held in the solvent.

• Consequently, the solubility of the solid solute decreases as the temperature goes down.

Multiple Choice

What generally happens to the solubility of a solid in a liquid when the temperature goes up?

• It increases

• It decreases

• It stays the same

• It cannot be determined

​

​

Reading Solubility Curves

• A solubility curve shows how much solute dissolves at a specific temperature.

• First, find the line for the substance and the temperature on the x-axis.

• Follow the temperature line up to the substance's curve.

• Read the corresponding solubility on the y-axis in g/100g H₂O.

Multiple Choice

On a standard solubility curve, what information is found on the x-axis?

• Temperature

• Solubility in grams

• The name of the substance

• The type of solvent

​

Common Misconceptions

Misconception	Correction
The terms 'solute' and 'solvent' are interchangeable.	The solute is what dissolves; the solvent is what does the dissolving.
You can dissolve an unlimited amount of a solid in a liquid.	A liquid has a limit to how much solid it can dissolve.
A solubility curve is just a random line.	It shows a substance's exact solubility at different temperatures.

Multiple Choice

Why is it important to know the temperature when determining the maximum amount of salt that can dissolve in water?

• Because temperature changes the color of the salt.

• Because the maximum amount of solute that can dissolve changes with temperature.

• Because the salt only dissolves at its boiling point.

• Because temperature determines if the salt is a solute or a solvent.

Multiple Choice

If you want to dissolve more sugar in your iced tea, what is the most effective method based on the principles of solubility?

• Stir the tea more vigorously.

• Use a larger glass.

• Warm the tea up before adding sugar.

• Add ice to the tea first.

Multiple Choice

A scientist needs to dissolve 40g of ammonium chloride (NH₄Cl) in 100g of water. According to a solubility curve, this is possible at 50°C. What would happen if they tried to dissolve the same amount in water at 20°C?

• It would dissolve much faster.

• More than 40g would be needed.

• Not all 40g of the solute would dissolve.

• The solution would become a gas.

Multiple Choice

A solubility curve shows how much solute dissolves at different temperatures. How do you find the solubility of a substance at a specific temperature?

• Find the solubility on the y-axis first, then go horizontally to the curve

• Find the temperature on the x-axis, go up to the substance’s curve, then read the solubility on the y-axis

• Use the highest point of the curve regardless of the temperature

• Estimate the solubility by averaging the solubilities of other temperatures

​

Summary

• A solute dissolves in a solvent to form a uniform solution.

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

• Solubility curves graph the relationship between temperature and solubility for a substance.

• Read a solubility curve by tracing from temperature to the substance's solubility.

Poll

On a scale of 1-4, how confident are you about reading a solubility curve to find the amount of solute that dissolves at a certain temperature?

• 1

• 2

• 3

• 4