Mixtures

 

Objective

At the end of the lesson, you should be able to:

• discuss mixture and its type; and
• differentiate solutions, suspensions, and colloids.

Mixture

• It is composed of two or more pure substances combined through physical means in varying proportions.

• Each pure substance in a mixture retains its property.
• The components of a mixture can be separated by physical means depending on the states of the pure substances in a mixture.
  
• It can be classified into two namely homogeneous and heterogeneous mixtures.

Homogeneous Mixture

• It has uniform composition and properties.
• It has only one phase in which it is hard to determine the components of the mixture visually.

Example

A salt solution is a homogeneous mixtures.

Heterogeneous Mixture

• It has varying composition and properties.
• It may have two or more phases since the individual substance is visually distinct

Example

An oil and water mixture is a heterogeneous mixture.

Solution, Suspension and Colloid

• Mixtures can also be classified based on particle size namely solution, suspension, and colloid.
• A solution is a homogeneous mixture while a suspension and a colloid are heterogeneous mixtures.

1. Solution

• It has two or more substances uniformly dispersed throughout the mixture. It forms a single phase
• It has the smallest particle size. Particles of a solution are invisible to the naked eye.

2. Suspension

• The components of a suspension separate over time due to the influence of gravity.
• It has the largest particle size compared to the other types of mixtures. The particles in a suspension are visible to the naked eye

3. Colloid

• The particles in a colloid only remain suspended in the medium when viewed using a microscope.
  
• It has an intermediate particle size compared to solutions and suspensions. The particles appear to be invisible to the naked eye.

Examples

• Solution: salt-water mixture and metal alloys.
• Suspension: soil-water mixture
• Colloid: milk and paint

Tyndall Effect

Colloidal particles exhibit Brownian movement and cause Tyndall effect.

• Brownian movement is the random movement of particles suspended in gas or liquid.
• This random motion of particles causes the scattering of light or Tyndall effect. Tyndall effect is usually demonstrated by passing a ray of light through a sample mixture.
• Tyndall effect could be used to identify the mixture as solution, colloid, or suspension.

• When light passes through a given mixture, the mixture is a solution.
• When light does not pass through a given mixture, the mixture is a suspension.
• When light passes through a given mixture and the light scatters, the mixture is a colloid.

Key Points

• A mixture is composed of two or more pure substances combined through physical means in varying proportions. Its components retain its property and can be separated by physical means.
• Mixture can be classified into two.
  • A homogeneous mixture has uniform composition and properties and has only one phase.
  • A heterogeneous mixture has varying composition and properties. It may have two or more phases.
• Mixtures can also be classified based on particle size namely solution, suspension, and colloid. A solution is a homogeneous mixture while a suspension and a colloid are heterogeneous mixture.
  • A solution has two or more substances uniformly dispersed throughout the mixture. It has the smallest particle size.
  • A suspension has the largest particle size. The components of a suspension separate over time due to the influence of gravity.
  • A colloid has an intermediate particle size. The particles in a colloid remain suspended in the medium. However, it appears to be invisible to the naked eye.
• Colloidal particles exhibit Brownian movement and cause Tyndall effect.
  • Brownian movement is the random movement of particles suspended in gas or liquid.
  • Tyndall effect is the scattering of light.