The homogeneous mixtures are uniform in nature and consist of a single phase. In contrast, heterogeneous mixtures are not uniform. It means that if two samples are taken from a heterogeneous mixture, the chemical composition of these samples does not come out to be identical. 

Solutions are homogeneous mixtures made from dissolving solute/ solutes in a solvent. In solutions, a solute does not get filtered out from a solution if passed from a filter paper. Contrary to this, suspension and colloids are a heterogeneous mixture.  

Suspension

Suspensions are the type of heterogeneous mixtures of solid particles in a fluid. Unlike a solution, the solid particles in a suspension are large enough for sedimentation. When we define suspension, it is also crucial to remember that the solid particle in suspensions must be larger than one micrometre and may be visible to naked eyes. If a suspension is left undisturbed for some time, its solid particles settle down. But, a mixture is known as a suspension only when and until the particles do not settle down. No matter how many times or how hard one tries to dissolve the solid particles in a suspension, they do not get dissolved. 

The physical appearance of a suspension

Can one visually identify if a mixture is a suspension? Yes, unlike solutions in which particles do not float in the liquid, particles float in a suspended mixture in suspensions. Suspensions are not uniform in colour and might also appear to be cloudy or murky. 

Properties of suspensions

• Suspensions are heterogeneous mixtures. It is because the solute particles in a suspension do not get dissolved in the solvent and instead get suspended in it and float freely in the medium. 
• Suspensions have two phases- the internal phase and the external phase. The internal phase is solid particles that get dispersed in the external phase, which is a fluid, via mechanical agitation to form a suspension. 
• In contrast to solutions, the suspended particles of suspensions are visible under a microscope.
• If a suspension is kept undisturbed for some time, the suspended particles settle down. 
• Dispersed phase and dispersion medium are the two terms used to classify suspension. Dispersed phases are necessarily solid, whereas a dispersion medium can be solid, liquid or gas. 
• The large particle size of suspensions enables them to exhibit the Tyndall effect, i.e. they scatter light. 
• However, if the particle of a suspension settles down, it no longer scatters light.
• The suspension particles can be separated with filtration. 
• Suspensions are unstable if considering a thermodynamic point of view. But, they are kinetically unstable. This also defines the shelf life of suspension. 

Examples of suspension

1. Milk of magnesia, i.e a mixture of Magnesium hydroxide with water
2. A mixture of sand and water
3. Lemonade
4. Flour suspended in water
5. Mud in water
6. A mixture of chalk and water
7. Water-based paints
8. Calcium hydroxide (slaked lime) with water

How are suspensions different from colloids?

• Definition

Suspensions: These are heterogeneous mixtures that have particle sizes above 100 nm. 

Colloids: Heterogeneous mixtures with particle sizes ranging between 1 nm and 100 nm. 

• Particle visibility

Suspensions have particles that can be seen with naked eyes. 

Colloids have particles that are not visible with naked eyes. 

• Permeability through filter paper

Particles of suspensions do not pass through filter paper, i.e. they get filtered out. 

The particles of colloid are not large enough. Hence, they can pass through a filter paper and do not get filtered out.

• Sedimentation

Suspensions undergo sedimentation. 

Colloids do not undergo sedimentation.

Differences between solutions and suspensions

• Solutions are defined as homogeneous mixtures. But, when we define suspension, they are known to be a type of heterogeneous mixture.
• Solutions have their particles at the ion or molecular level. The size of particles in solutions is very small. Therefore, not visible with naked eyes. Particles of suspensions are easily visible with naked eyes due to their large size. 
• The solute and solvent of a solution do not separate if left undisturbed. Whereas the components of suspensions separate. 
• The transparency of solutions allows light to pass through them. But, suspensions are opaque. Their opaqueness makes it unable for light to pass through them. 

Conclusion

Suspensions get often misunderstood as solutions. But, they are similar to the solutions only if we regard them as mixtures. The suspensions are heterogeneous mixtures of solid particles in a liquid, solid or gaseous medium. They have unique properties like undergoing sedimentation, exhibiting the Tyndall effect, large particle size etc. Some of the standard suspension chemistry examples are sand in water, milk of magnesia and numerous others. The two components of a suspension are known as the dispersed phase and dispersion medium. A mixture is qualified as a suspension only when the dispersed phase is solid, and the dispersion medium can be liquid, solid or gas.