Lecture 2 – Dissolving, Filtration and Evaporation

ACKNOWLEDGEMENT:

Figure	Source of Figure
Figure 1	seanlinnane.blogspot.com
Figure 2	seanlinnane.blogspot.com
Figure 3	cnx.org
Figure 4	science.taskermilward.org.uk

Technique 1: Dissolving, Filtration and Evaporation

Separating a mixture of Sand and Salt:

This technique is used to separate a mixture of 2 solids, out of which one dissolves in some liquid. Here, an example of a mixture of sand and salt is taken. Salt is soluble in water.

i.                    Dissolving the mixture in water:

Ø The mixture is dissolved in water

Ø Salt being soluble, dissolves in water, while sand remains undissolved

Ø
Figure 4a:

ii.                  Filtration of the solution:

Ø The mixture is filtered

Ø Sand collects as residue in the filter paper. It is washed thoroughly with water to flush out any traces of salt solution and dried

Ø
Figure 4b

iii.                Evaporation:

Ø The filtrate is heated to evaporate excess water to obtain salt

Ø
Figure 4c 

Evaporation & Crystallization:

Water is evaporated from the salt solution to yield salt. This evaporation can be done using high amount of heat which can evaporate the water quickly to yield salt. However, the shape/physical form of this salt is amorphous and appears to be powdered. To obtain, proper salt crystals from the solution, Crystallization must be done.

Crystallization is the evaporation of excess water in a slow, steady and natural way to obtain regularly shaped salt crystals. Crystallization allows the crystals to keep their water of crystallization which is necessary for their proper shape.  

Figure 4d: Shows a method to obtain crystals of a solid by slow evaporation.

Note: Slower the rate of evaporation/crystallization, the bigger/larger the crystals are formed and vice versa.