Page 43 - Science Class 07

Change of colours of indicators in acidic
solu ons:
Take a few drops of lemon juice in a test tube.
Indicator Change of Colour Now, test it with a litmus paper. What will you
observe? You will observe that the colour of
Blue litmus Red
the blue litmus paper has turned into red.
Red litmus Red Similarly, you can use other indicators such as

Phenolphthalein Colourless red litmus, phenolphthalein and methyl
orange.
Methyl orange Orange

Physical Proper es of Acid v Acid does not show any effect when it is

v Acids have sour taste. poured into an acidic solu on.
v Acid turns blue litmus red. v Some acids are soluble in water.

v Acid turns methyl orange solu on orange. v Strong acid like hydrochloric acid and
sulphuric acid are corrosive in nature.

Collect a li le amount of juice from the following eatable items and with the help of
different indicators try to find out whether the given juice is acidic or not.

Eatable items Indicator used A cidic (Yes/No)

Mango
Tomato

Lemon
Grapes

Rice
Onion

Guava
Orange

Apple
Potato

Wheat
Pumpkin

Uses of Acids Hydrochloric Acid
Hydrochloric acid, sulphuric acid and nitric acid Its main uses are as follows:
are the most commonly used acids in the v In the oil industry, it is used to dissolve oil-
laboratory as well as in several industries. bearing rocks.

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