Separation Techniques Lesson for Grade 4 Students

Filtration and Evaporation

Sylvia and her family were out camping in the Appalachian trail. They had read ‘A walk in the Woods’ by Bill Bryson. The descriptions in the book had captivated the family. So, at the first opportunity, they set out. The first two days were exhilarating. Sylvia and her brothers found all sorts of insects. And other small creatures. On the third day, calamity struck. One of the water cans tipped over. All the precious drinking water spilled to the ground. The family was alarmed, but Sylvia’s father said that he knew some separation techniques to get drinking water from muddy water. He collected some muddy water from the pool nearby. Using his white handkerchief as a filter, he collected some water for drinking. Sylvia was very impressed. She made up her mind to ask her science teacher Mr. Johanssen about such separation techniques.

Sylvia: Good morning Mr. Johanssen.

Mr. Johanssen: Oh Sylvia. Welcome back. How did the trip go?

Sylvia: It was great fun! Especially the part where dad had to filter water! I wanted to ask you about such separation techniques.

Mr. Johanssen: Do you mean separation techniques to separate the substances in a mixture?

Sylvia: Yes.

Mr. Johanssen: So, you are talking about physical methods such as filtration.

Sylvia: Isn’t filtration used to separate an insoluble solid from the liquid in a mixture?

Mr. Johanssen: Exactly. What you do is let the liquid pass through a filter paper.

Sylvia: Filter paper has tiny pores that allow the liquid to pass through, right?

Mr. Johanssen: Yes, but the insoluble solid particles cannot pass through. They are left behind.

Sylvia: I see.

Mr. Johanssen: The insoluble solid is called residue. The liquid that passes through the filter paper? It is called filtrate.

Sylvia: Is filtration used to purify water everywhere?

Mr. Johanssen: In most countries, filtration is one of the stages of water treatment.

Sylvia: With just filter paper?

Mr. Johanssen: Oh no. The raw water is filtered through layers of sand beds. These sand beds contain sand grains of different sizes.

Sylvia: So, the sand filters help to trap suspended particles while allowing clear water to run through

Mr. Johanssen: Excellent. You got the concept right.

Sylvia: Why can’t waste water be filtered like this to remove impurities?

Mr. Johanssen: Many industries do that. For example, in the textile industry, they treat their waste water before recycling for further use.

Sylvia: I see. Can you tell me about any other separation techniques?

Mr. Johanssen: Yes. Evaporation is another method.

Sylvia: Can you give an example?

Mr. Johanssen: Yes, we can use evaporation to separate salt from sea water. When the liquid in the mixture has completely evaporated, the residue is the solid salt.

Sylvia: Is this done on a small scale?

Mr. Johanssen: This can be done on a small scale. But in some parts of the world this is done on a large scale.

Mr. Johanssen: The sea water is allowed to flow into large flat areas called salt pans. The sun helps to evaporate the water, leaving salt behind.

Sylvia: How do they do that?

Sylvia: Amazing. During our camping trip I really realized how important water is. We waste a lot of water in daily life, I think.

Mr. Johanssen: You are right, Sylvia. Youngsters like you should start conserving water. At home, try washing dishes in a tub of water instead of under a running tap.

Sylvia: I can also turn off the tap while brushing teeth. I will tell my siblings and parents too. We can use a cup of water to rinse our mouth.

Mr. Johanssen: Excellent. You can also reuse water that has been used to wash vegetables to water your plants.

Sylvia: That is a very good idea. I think we should always check for leaking or broken taps and pipes too. Sometimes a lot of water is wasted like that.

Mr. Johanssen: You are right. Water is absolutely essential in daily life for an individual, but it is also used in industries. Agriculture, mineral water industries, textiles and oil refineries all depend heavily on water.

Sylvia: I can see why it is so important to conserve water. It is truly life-giving.

Mr. Johanssen: You are right, Sylvia. You are on the right track. Got to go now. See you in class.

Sylvia: Thank you, Mr. Johanssen.