Is Matter Around Us Pure? Blog 10

Hello Learners,

Let us continue from the previous blog......

(H) How can we obtain pure Copper Sulphate from an Impure sample?

Principle: Crystallisation- Crystals are the purest form of a substance having definite geometrical shapes. Crystallisation is a process that separates a pure solid in the form of its crystals form a solution. This is one of the most commonly used techniques for purification of inorganic/organic solids. This is based upon the principle that when a crystal is formed, it tends to exclude the impurities which remain in the solution.

Activity 2.8 wants us to separate impurity from copper sulphate by heating its solution.

Observation:

Pure Copper sulphate forms as a crystal.  

Explanation:

Crystallisation is a property of some salts. In an over-saturated solution of the salt, molecules of salt join to form small clusters. These small clusters have a fix molecular arrangement. We call such clusters as crystals.

Here we heat a solution of copper sulphate. Heating produces a saturated solution of the salt. When this solution cool, over saturation results in the formation of copper sulphate crystals. Molecules of a crystal do not contain any impurity. As a result, we get pure copper sulphate.

https://www.youtube.com/watch?v=SAU-gptAFe0

Application: 1. During evaporation, the solution is heated to dryness. During this heat treatment, some solids may decompose or some solids, like sugar may get charred.

2. Both for evaporation or crystallization the solution of the impure solid is prepared in water or any other suitable solvent. This solution is then filtered to remove insoluble and suspended impurities.

3. The salt that we get from sea water contains a number of impurities. To remove these impurities the process of crystallization is used.

4. Crystallisation can also be used to obtain pure alum (phitkari), nitre(potassium nitrate) etc from impure samples.

Purification of Drinking Water

Harmful bacteria, suspended solid, colloidal clay particles are removed for water before supplying to our homes. It involves the following process.

Sedimentation: The water is allowed to stand for some time, during this time, many suspended solids settle down at the bottom of the tank.

Loading tank:  Small suspended low density particles are removed by the process of loading. In the loading tank, some alum is added to the water. It should be noted that the colloidal particles of the clay present in water are negatively charged. They do not settle down in the sedimentation tank. However, when alum is added, their negatively charged particles get neutralized by the positively charge aluminium ions present in alum. In this way, colloidal particles get neutralized by the positively charge aluminium ions becomes heavy and settle down at the bottom of the tank.

Filtration Tank: After the removal of insoluble solids and other suspended impurities, the water is passed through a filtration tank. The filtration tank has three layers.

Chlorination Tank:  The water obtained from the filtration tank is introduced into the chlorination tank where it is treated with bleaching powder or some other germicide such as ozone to kill bacteria. The water obtained after the above treatments is free all types of impurities and bacteria and is supplied to our homes for drinking purpose.

                          https://www.youtube.com/watch?v=qbCU5vk1QT4

Physical and Chemical Changes

https://www.youtube.com/watch?v=yggw_tEEEXU

Home Assignment

1. Complete the notes in your chemistry notebook.

2. Do in-text question in your note book.
3. Tabulate the difference between chemical and physical changes. 
4. Make a list of examples of chemical and physical changes.