Preparation of Colloidal Solution of Sulphur

Introduction to the Experiment

The aim of this experiment is to prepare a colloidal solution of sulphur and to differentiate it from a true solution and a suspension based on transparency and filtration.

To prepare a colloidal solution of sulphur in water, hydrogen sulphide gas must be oxidised by adding concentrated nitric acid as per the following reaction:

H₂S (aq) + 2HNO₃ (aq) → 2H₂O (l) + S (s) + 2NO₂ (g)

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

Experiment Procedure

To perform this experiment, the apparatus and material required are

Apparatus and Material:

• Distillation Flask
• Laboratory Thermometer (-10 °C to 110 °C)
• Condenser
• Two Beakers (250 mL)
• Tripod Stand
• Wire Gauze
• Single Bore Cork
• Burner
• Iron Stand

Materials:

• A mixture of Water and Acetone

Steps to follow for the preparation of colloidal solution:

Procedure

True solution of common salt

• Take a dry, clean beaker of 100 mL capacity labelled ‘1’  and fill it with 40 mL distilled water.
• Add 4 g sodium chloride to the beaker and stir using a glass rod.
• Sodium chloride dissolves completely to form a transparent solution that cannot be separated through filtration.
• Hence, we can say it is homogeneous and a true solution.

Colloid of sulphur

• Take a dry, clean beaker of 100 mL capacity labelled ‘2’ and fill it with 40 mL distilled water.
• Using Kipp’s apparatus, pass H₂S gas into the beaker and then add conc. HNO₃ to it in order to obtain a mixture of sulphur in water.
• Sulphur forms a translucent mixture in water, and the particles keep moving in the beaker.
• These particles cannot be separated through filtration.
• Hence, we can say it is heterogeneous and a colloid.

Suspension of chalk powder

• Take a dry, clean beaker of 100 mL capacity labelled ‘3’ and fill it with 40 mL distilled water.
• Add 4 g chalk powder to the beaker and stir using a glass rod.
• Chalk powder does not dissolve in water, forming an opaque, muddy solution.
• Its particles can be separated through filtration.
• Hence, we can say it is heterogeneous and a suspension.

Conclusion

We conclude that:

• We have prepared one sample each of a true solution, a colloidal solution and a suspension.
• A colloidal solution is translucent, a suspension settles down after a while, forming two separate layers, and the true solution is transparent throughout.
• A colloidal solution and a true solution cannot be separated into their constituents by filtration, whereas a suspension can be separated.

FAQs on Preparation of Colloidal Solution of Sulphur