Rate of Dissolution

Rate of Dissolution

Middle School

​

Learning Objectives

• Define the rate of dissolving and identify the solute and solvent in a solution.

• List the three main factors that influence the rate at which a solute dissolves.

• Explain how stirring, temperature, and particle size each affect the speed of dissolving.

• Apply this knowledge to determine the best way to dissolve a substance quickly.

Key Vocabulary

​

Solute

The substance that gets dissolved in a solution, like sugar in tea.

​

Solvent

The substance that dissolves the solute, such as water in iced tea.

​

Rate of Dissolving

A measure of how fast a solute dissolves within a specific solvent.

​

Solution

A uniform mixture that is formed when a solute dissolves in a solvent.

Factors Affecting the Rate of Dissolving

​

Stirring

• Stirring a solute in a solvent makes it dissolve much faster.

• This action helps to spread the solute particles throughout the solvent.

• It increases contact between the solute and the solvent particles.

​

Temperature

• A solute generally dissolves much faster in a warmer solvent.

• Warmer solvent particles have more energy and move around more quickly.

• This leads to more frequent collisions with all the solute particles.

​

Particle Size

• Smaller solute particles will dissolve much faster than the larger particles.

• They have a greater total surface area for the same amount.

• This allows for more contact between the solute and the solvent.

Multiple Choice

What factor is being demonstrated when granulated sugar dissolves more quickly than a sugar cube?

• Temperature of the solvent

• Stirring the solution

• Particle size of the solute

• The type of solvent used

​

Common Misconceptions About Dissolving

Misconception	Correction
Dissolving is the same as melting.	Dissolving is mixing a solute in a solvent. Melting is a state change.
Stirring is what makes a substance dissolve.	Stirring only speeds up dissolving; it does not cause it to happen.
Any amount of a solute can be dissolved in a solvent.	Solvents have a limit to how much solute can be dissolved at a temperature.

Multiple Choice

Why does sugar dissolve faster in hot tea compared to iced tea?

• The sugar particles are smaller in hot tea.

• The water particles in hot tea have more energy and move faster.

• The tea is less dense when hot.

• Hot tea chemically changes the sugar.

Multiple Choice

If you want to dissolve bath salts in your bathwater as quickly as possible, what combination of actions should you take?

• Use cold water and don't stir.

• Use hot water and stir the salts in.

• Use a large, single block of salt in cold water.

• Let the salt sit at the bottom of the tub without stirring.

Multiple Choice

A student adds a spoonful of sugar to two identical glasses of water. They stir one glass but not the other. What is the expected outcome?

• The sugar in both glasses will dissolve at the same rate.

• The sugar in the unstirred glass will not dissolve at all.

• The sugar in the stirred glass will dissolve faster.

• Stirring makes the water colder, slowing down dissolving.

Multiple Choice

You need to sweeten a pitcher of cold lemonade for a party. To make the sugar dissolve fastest, what form of sugar should you use?

• Large sugar cubes

• Rock candy crystals

• Standard granulated sugar

• Fine powdered sugar

​

Summary

• The rate of dissolving measures how quickly a solute dissolves in a solvent.

• Stirring, temperature, and particle size affect how fast a substance dissolves.

• A higher temperature gives solvent particles more energy to break down the solute.

• Smaller solute particles have a larger surface area, dissolving them faster.

Poll

On a scale of 1-4, how confident are you about the factors affecting the rate of dissolution?

• 1

• 2

• 3

• 4