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Physical changes/chemical changes

Everyday you come across many changes in your surroundings. These changes may be physical changes/chemical changes. These changes may involve one or more substances. For example, your mother  may ask you to dissolve sugar in water to make a cold drink. Similarly, setting curd from milk us a change.

Sometime, milk becomes sour . Souring of is a change. Stretched rubber band also represent a change.

Physical and chemical changes

Here in this blog you will know the nature of these changes. These changes are of two kinds physical changes/chemical changes

Physical changes/ chemical changes.

First of all telling about Physical changes.

Let us do one thing

  • Cut a piece of paper in 4 square pieces.
  • Cut each square pieces futher into 4 square pieces.
  • Lay these pieces on the floor or a table so that the pieces acquire the shape of the original piece of paper.

Obviously you can’t join the pieces back to make the original piece, but is there is a change in the property of the paper.

Is this physical changes/chemical changes?

In doing this , you saw that paper changes it’s size. Properties such as shape , size, colour , state of a substance are called it’s physical properties.

A change in which a substance undergoes a change in its physical properties is called a physical changes

Now friends, let us do one more thing

  • Dissolve about a teaspoon of copper sulphate in about half a cup of water in a glass tumbler or a beaker.
  • Add a few drops of Dilute sulphuric acid to the solution.
  • The solution become blue in colour
  • Save a small sample of the solution in a test tube or a small glass bottle.
  • Drop a nail or a used shaving blade into the remaining solution.
  • Wait for half an hour or so
  • Observe the colour of the solution.
  • Compare it with the colour of the sample solution saved separately.

Do you see any change in the colour of the solution?

Take out the nail or the blade.

The changes that you notice are due to a reaction between copper sulphate and iron. The change of colour of the solution from blue to green is due to the formation of iron sulphate,a new substance.

The brown deposit on the iron nail is copper, another new substance.

Is this physical changes/chemical changes?

In doing this you saw that in each change, one or more new substances were formed. A change in which one or more new substances are formed is called chemical changes

 

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