What are mixtures?

1. Mixtures are combinations of two or more substances which are not chemically joined together. Each substance retains its own chemical and physical properties.

2. Mixtures can be divided into two main groups - homogeneous and heterogeneous. 

The table below shows the differences between homogeneous and heterogeneous mixtures.

What is a solution?

A solution is a mixture consisting of particles of two or more substances that are distributed evenly throughout.

Examples of Solutions

In a solution, the solute is dispersed uniformly throughout the solvent. A solution can be formed by a solute and a solvent of the same or different physical states.

Characteristics of an Aqueous Solution

1. Water is called the universal solvent as many substances can dissolve in it.
e.g. human bodies contain about 75 to 85% of water which contains many dissolved chemicals, minerals and nutrients.

2. An aqueous solution is a solution in which the solvent is water.

3. An aqueous solution is a solid-liquid mixture with the following characteristics:

- It cannot be filtered. No residue is left on the filter paper when filtration is carried out as the solute particles are so small that they can pass through the pores of the filter paper.

- It is clear and transparent. Light is able to pass through as the solute particles are too small to block any light passing through the solution.

- When left to stand, no particles sink to the bottom of the container.

What is a suspension?

1. A suspension is a mixture containing insoluble solid particles suspended in a medium.

2. In a suspension, a solute does not dissolve in the solvent. The solute particles are large enough to be clearly visible when suspended in a solvent. Examples of suspensions are gastric medicine, calamine lotion, haze and muddy water.

3. The characteristics of a suspension:

- A suspension can be separated by filtration. Residues are left on the filter paper as the solute particles are too large to pass through the pores of the filter paper.

- It does not allow light to pass through and scatters light. Light is unable to pass through a suspension as the solute particles are large enough to block any light passing through the suspension.

- When left to stand, the particles settle to the bottom of the container.

Watch the video below to learn more about how a solution differs from a suspension.

Comparison Between Solutions and Suspensions

The table below shows the differences between solutions and suspensions.

What does concentration of a solution mean?

Concentration of a solution is a measure of the amount of solute dissolved in a given amount of solvent.

There are dilute, concentrated and saturated solutions.

Calculating the Concentration of a Solution

The concentration of a solution can be calculated by using the formula below.

What is solubility?

Solubility is the maximum amount of solute which can dissolve in 100 g of water at a fixed temperature. 

When a solvent is able to dissolve in a solvent, it is soluble. When a substance is not able to dissolve in a solvent, it is called insoluble.

There are three factors that affect solubility.

Solubility Curve

A solubility curve is a graph showing the maximum amount of a solute that can dissolve in 100g of water at a given temeprature to form a saturated solution.

The features of a solubility curve are shown below.

Interpreting the Solubility Curve

Refer to the figure below to learn how to derive information from a solubilty curve.

Rate of Dissolving of Substances

Rate of dissolving is a measure of how fast a solute dissolves in a fixed amount of solvent completely. It is also called the rate of solvation or dissolution. 

The rate of dissolving is affected by the following factors.