Diffusion of Gases and Liquids (KPT) Practical.

This lab session, we investigated diffusion in Gases and Liquids.

Introduction to the experiment's aims and theories tested:

• The Kinetic Particle Theory (KPT) explains the way in which matter behaves and its physical properties in terms of the movement of the tiny particles the matter is made up of.
• Diffusion is a physical phenomenon that takes place in liquids and gases where the particles spread out and travel away in a haphazard and random way.
• Gases diffuse at different rates.
• Lighter particles travel faster than heavier ones (at the same temperature).
• Particles also move faster at higher temperatures, compared to lower temperatures.
• Diffusion takes place slower in liquids due to its lower kinetic energy.
• In liquids and gases when diffusion is taking place, a process called intimate mixing takes place.
• Intimate mixing: When collisions are taking place between these particles, the KPT states that there is sufficient space between the particles of one substance (the substance with larger particles) for the particles of another substance (the substance with smaller particles) to move into.

Aims:

• To infer and observe the properties of particles of matter
• To investigate relationships between the rate of diffusion and density(mass) of gas
• To investigate and observe the diffusion of liquid in water.

Procedure of experiment part 1:

1. Add 50 cubic cm of beans to a measuring cylinder
2. Add 50 cubic cm of sand to the same measuring cylinder.
3. Mix the 2 solids by shaking the mixture well and then, let it settle.
4. Measure the volume of the mixture.

Observations:

The volume of the mixture is 88 cubic cm although the addition of the 2 original volumes of the beans and sand is actually 100 cubic cm.

Conclusion:

When equal volumes of sand and beans are mixed, the total volume is less than the 2 volumes added together. The lesser volume is caused by the spaces in between the beans. The smaller particles of sand occupy the spaces in between the beans, causing the volume to be lesser.

Procedure of experiment part 2:

1. Fill up half the plastic tube with water.
2. Top up the remaining half of the tube with alcohol. (make sure the 2 liquids do not mix and there is an interface indicating the 2 layers of liquids)
3. Hold the tube with your thumb covering the opening of the tube fully.
4. Hold on and invert the tube a few times, taking note of the sensation the mixing creates on the thumb.
5. Hold the tube back upright.

Observations:

The final total volume of the alcohol and water became lesser than the sum of the original two volumes of the 2 liquids (the level (height) of total liquid in the tube dropped). A strange sensation (like being suctioned) was created on the thumb while the tube was inverted.

Conclusion:

When equal volumes of alcohol and water are mixed, the total volume is lesser than the 2 volumes added together. Also, the thumb used to cover the tube feels like its being suctioned. This is because when the tube is inverted, the alcohol particles, which have a lower density than water will rush upwards (towards the bottom of tube) while the water particles will rush downwards (towards the thumb) as they have a higher density. During this, the smaller water particles will collide with the alcohol particles and fill in the spaces between the alcohol particles. Thus, the total volume will decrease. Also, as the spaces in between the small water particles (which cannot be filled by alcohol particles as they are much larger) are not filled, there is vacuum between the solution and the thumb. As the pressure in a vacuum is much lower than that in normal atmosphere conditions, the thumb will feel as if its suctioned in.

Procedure of Teacher's demonstration: 

1. Two pieces of cotton wool is placed at the 2 ends of a hollow tube and held by a retort stand.
2. One cotton wool is soaked in concentrated hydrochloric acid of relative molecular mass, 36.5. (this end of the tube is called A)
3. The other is soaked with concentrated ammonia solution of relative molecular mass, 17. (this end of the tube is called B)
4. Stoppers are placed at both ends to seal the tube and then, teh set-up is observed.

Observation:

A white ring is observed nearer to end A (the Hydrochloric acid).

Conclusion:

Ammonia Gas diffuses faster than Hydrochloric acid. As Ammonia solution has a smaller mass than Hydrochloric acid, it diffused and travelled faster towards the other end (which is end A) and thus, the white ring of Ammonium Chloride (Solution formed when HCl and NH3 mix) formed nearer end A. This proves that the smaller the mass of the gas is, the faster the rate of diffusion is as well.

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