In this video, we will focus on separation of insoluble solid from a liquid.
Chemistry is everywhere
Let’s say you are really hungry and are craving badly for a bowl of hot steamed rice.
Before steaming, let’s wash the rice. You stir the rice and pour away the water. You add water again for a second wash. You may choose to simply pour away the water again, but you know that by doing that, a little amount of water will remain in the bowl. You, being a meticulous Chemistry student, decided to pour the mixture into a kitchen sieve to get rid of all water
Now you do realise, when we wash the rice in water, the rice did not dissolve in the water. This is because rice is insoluble in water. We can simply use a kitchen sieve to separate rice and water because the size of a rice grain is bigger than the hole of the kitchen sieve. The act of separating insoluble solid from a liquid, is called filtration in chemistry terms. Yes. Chemistry is everywhere, even in your home kitchen.
Separation of sand and water
Now, let’s say we have a mixture of sand and water. If sand is added into water, sand does not dissolve at all, just like rice. Hence, sand is insoluble in water. To separate sand and water, we can use the physical method, filtration, just like how we separate rice and water. However, the size of each sand grain is small, smaller than the holes of the kitchen sieve. If we pour the mixture, both sand and water will flow through the sieve.
So, what shall we do?
We will pour the mixture through the filter paper. The filter paper will act as a sieve. There are small pores on the filter paper. The size is so small, only water can pass through. The solid particles that are bigger than the pores of the filter paper will not be able to do so.
Let’s prepare the filter paper. The filter paper you see in a Chemistry Lab is round. We will fold it in half, then a quarter. Split open one flap, leaving 3 flaps at the other side. You should achieve a cone. Place this filter paper cone into a filter funnel.
Pour the mixture into the filter paper. You will realise, sand will remain in the filter paper. Water will flow through, into the conical flask.
Residue and Filtrate
Upon filtration, the solid that remains on the filter paper is called the residue. In this case, sand is the residue.
The liquid that passes through the filter paper is called the filtrate. In this case, water is the filtrate.
What if we have a mixture of sand and copper(II) sulfate solution? How do we separate this mixture and achieve sand and copper(II) sulfate crystals? Think about it. I will go through with you in the upcoming video.