Learning Objectives

• Define an aqueous solution and identify the solute and the solvent within it.

• Describe the concepts of concentration, dilution, and the solubility of a substance.

• Explain the various factors that can affect the rate at which a substance dissolves.

Key Vocabulary

Aqueous Solution

A solution in which the solvent is water, resulting in a uniformly mixed substance.

Solvent

The substance that exists in the greatest quantity in a solution and dissolves the other substance.

Solute

The substance that is dissolved in a solvent to form a solution, and exists in a lesser quantity.

Concentration

A measure of how much solute is dissolved within a certain amount of the solvent.

Solubility

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

Dilution

The process of reducing a solution's concentration, typically by adding more solvent to it.

What is an Aqueous Solution?

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

• An aqueous solution is a specific type where water is the solvent.

• The solute is the substance that gets dissolved in a solution.

• In seltzer, carbon dioxide (CO₂) is the solute and water is the solvent.

States of Matter in Solutions

Solid Solutions

• ​These are solutions where the solvent is a solid, creating a mixture.

• ​​A saxophone is a solid solution of solid copper and solid zinc.

• ​The state of the solvent determines the final state of the solution.

Liquid Solutions

• ​Liquid solutions are formed when solutes dissolve in a liquid solvent.

• ​​Soda contains liquid water, gas CO₂, and solid sugar as solutes.

• ​Water acts as the solvent, dissolving both the gas and solid.

Gaseous Solutions

• ​Gaseous solutions are uniform mixtures of different gases, like the air.

• ​​Air is a solution where nitrogen is the solvent in greatest quantity.

• ​Oxygen and various other gases act as the solutes in the air.

Concentration and Dilution

• Concentration is how much solute is dissolved in a solvent.

• A solution with a lot of solute is called concentrated.

• A solution with very little solute is called dilute.

• Adding more solvent makes a solution less concentrated, or diluted.

Factors Affecting Rate of Dissolution

Heating the Solvent

• Heating a solvent makes its molecules move much faster.

• This causes more frequent collisions with the solute particles.

• More collisions mean the solute dissolves more quickly.

Stirring the Solution

• Stirring a solution increases the movement of the particles.

• It moves dissolved solute away from the undissolved solid.

• This exposes fresh solvent to the remaining solute particles.

Breaking Up the Solute

• Breaking the solute into smaller pieces increases its surface area.

• More of the solute is exposed to the solvent at once.

• This allows the solvent to dissolve all the particles faster.

Common Misconceptions

Summary

• An aqueous solution has a solute dissolved in a water solvent.

• Solutions can be solid, liquid, or gas, depending on the solvent.

• Solubility is the maximum solute that can dissolve at a certain temperature.

• Heating, stirring, or breaking up a solute makes it dissolve faster.