Difference Between True Solutions and Suspensions

This experiment aims to prepare solutions for various substances and to identify them as true solutions and suspensions.

A solution is a mixture of two or more components, namely solvent and solute. In general, the solvent is the component in a larger quantity, whereas the solute is the component in a smaller quantity.

Based on the size of particles, solutions can be divided into 3 types:

(i) True Solution

• It is a homogeneous mixture having a particle size smaller than 1 nm (10^-9 m) in diameter, thus not visible to the human eye.
• It is a stable solution that cannot be separated into its components through filtration.
• It appears clear and transparent.
• Its particles do not exhibit the Tyndall Effect.

(ii) Suspension

• It is a heterogeneous mixture having a particle size greater than 1000 nm (10^-6 m) in diameter, thus visible to the human eye.
• It is an unstable solution that can be separated into its components through filtration.
• It appears opaque.
• Its particles scatter a beam of light, i.e. exhibit the Tyndall Effect.

(iii) Colloid

• It is a heterogeneous mixture having particle sizes between 10^-9 m and 10^-6 m, thus visible to the human eye.
• It is a stable solution that cannot be separated into its components through filtration.
• It appears translucent.
• Its particles scatter a beam of light, i.e. exhibit the Tyndall Effect.

Apparatus and Chemicals Required

To perform this experiment, the apparatus and material required are:

Apparatus and Chemicals:

• 6 Beakers – 250 mL
• 6 Glass rods 
• 2 Filter papers
• 2 Funnels 
• 2 Ring stands
• Torch

Chemicals:

• Watch glass containing 5 g sodium chloride (common salt) 
• Watch glass containing 5 g sugar 
• Watch glass containing 5 g baking soda 
• Watch glass containing 5 g chalk powder 
• Watch glass containing 5 g fine sand
• Watch glass containing 5 g sulphur powder

Procedure

The true solution of common salt:

1. Take a beaker labelled ‘A’ of 250 mL filled with 100 mL distilled water.
2. Add sodium chloride to the beaker & stir the mixture using a glass rod.
3. Sodium chloride dissolves completely to form a clear & transparent solution.
4. This solution is stable as it does not change appearance after leaving for some time.
5. Its particles cannot be separated through filtration.
6. Hence, we can say it is homogeneous & a true solution.

The true solution of sugar:

1. Take a beaker labelled ‘B’ of 250 mL filled with 100 mL distilled water.
2. Add sugar to the beaker & stir the mixture using a glass rod.
3. Sugar dissolves completely to form a clear & transparent solution.
4. This solution is stable as it does not change appearance after leaving for some time.
5. Its particles cannot be separated through filtration.
6. Hence, we can say it is homogeneous & a true solution.

The true solution of baking soda:

1. Take a beaker labelled ‘C’ of 250 mL filled with 100 mL distilled water.
2. Add baking soda to the beaker & stir the mixture using a glass rod.
3. Baking soda dissolves completely to form a clear & transparent solution.
4. This solution is stable as it does not change in appearance after leaving for some time.
5. Its particles cannot be separated through filtration.

Conclusion

To conclude, the following are the learnings from this experiment:

• Sodium chloride, sugar and baking soda form stable and clear solutions, whereas chalk powder, fine sand and sulphur powder form unstable and opaque solutions. 
• Sodium chloride, sugar, and baking soda solutions pass through filter paper completely, whereas chalk powder, fine sand and sulphur powder solutions leave a residue on them.
• Solutions of sodium chloride, sugar and baking soda are homogeneous, whereas those of chalk powder, fine sand and sulphur powder are heterogeneous.
• Homogeneous mixtures do not scatter light, whereas heterogeneous mixtures scatter light. 
• Solutions of sodium chloride, sugar and baking soda are true solutions, whereas those of chalk powder, fine sand and sulphur powder are suspensions.

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