Question

A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the boxes shown in the given figure. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it. Q.1 Explain why the milk sample was illuminated. Name the phenomenon involved.​

Answer 1

Answer

Here the sample milk was illuminated as it was a colloid due to the Tyndall effect.

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• We know that there are three types of mixture

1. Solution
2. Suspension
3. Colloid

• Here the solvent and the solute gets mixed thoroughly and we can't see them seperately. An example would be the salt solution, here the Salt particles take a spot on the intermolecular spaces in water. A solution doesn't scatter light. They can't be seperately by filtering.
• A suspension is a substance where the solute particles settle down. Here they will scatter light and we can seperate the solute and the solvent by simply filtering.
• A colloid is a substance which is like a solution and also a suspension. Here the particles won't be dissolved completely nor settle down. They scatter light and this effect is called the Tyndall effect. This is because the particles are big enough to scatter light. And that's why the sample is illuminated. Centrifugation is the process used to seperate the mixture.

Answer 2

Answer:

1) Explain why the milk sample was illuminated ? Name the phenomenon involved.

➣ Milk is a colloid. If a beam of light is put on a milk sample contained in a beaker the path of light beam is illuminated and become visible when seen from the other side. This is because the colloidal particles are big enough to scatter light falling on them. This scattered light enters our eyes and we are able to see the path of light beam.

The scattering of light by colloidal particles is called Tyndall effect.

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