When a farmer uses excessive chemical fertilisers in the soil then the soil becomes acidic. Plants do not grow well when the soil is either too acidic or too basic. When soil is too acidic, it is treated with bases. If the soil is basic, organic manure is added to it. Organic manure release acids which neutralise the basic nature of the soil.

Add a drop of phenolphthalein separately in liquids A, B and C. The one which turns pink is sodium hydroxide, let it be A. Divide this into two parts. Now add a few drops of other solutions in the above solution taken into parts. The solution which again turns solution A colourless is hydrochloric acid. Let it be B. Then solution left is sugar.

We will put a drop each of hydrochloric acid, sodium hydroxide and sugar solution on the turmeric indicator. The liquid which changes the colour of turmeric indicator to red is basic in nature that is sodium hydroxide. Now, we will put a drop of sodium hydroxide on a drop of each of the other two liquids separately.
After that, we will put the drops of their mixtures on turmeric indicator. The drop which will change the colour of the turmeric indicator to red contains sugar solution.
This is because the mixture of base and the neutral solution is basic in nature. On the other hand, the drop which will not change the colour of turmeric indicator contains hydrochloric acid because hydrochloric acid reacts with sodium hydroxide forms a neutral solution.

(i) As all the chemicals present in lab may not be preferred to taste because they are harmful if you consume them.
(ii) Unknown substances may be responsible to burn the skin inside our mouth or in any other way it may harm our digestive system.
(iii)Pratik is cooperative, helpful and aware about scientific facts

The most commonly used natural indicator is litmus. It is extracted from lichens. It has a purple colour in distilled water. It is available in the form of a solution or in the form of strips of paper. It is available as red and blue litmus paper.

Place a drop of the liquid/a crystal of solid of the given acid on a moist blue litmus paper. If the colour changes from blue to red, it is an acid. Also metallic sodium gives hydrogen with brisk effervescence on reaction with an acid.

The effect of an ant bite can be neutralised by rubbing moist baking soda.

Neutralisation reaction.

Use both red and blue litmus solution and predict the colours in each case. In acidic medium, blue litmus solution turns to red. In basic medium, red litmus solution turns to blue

(a) Acidic oxides: Non-metals burn in oxide and form acidic oxides. These form an acid on treatment with water. Such oxides turn blue litmus red. For example, carbon dioxide (CO₂), sulphur dioxide (SO₂)
(b) Basic oxides: These are also called metallic oxides. These oxides form bases on treatment with water. These are generally basic in nature and turn red litmus blue. For example, sodium oxide (Na₂O), magnesium oxide (MgO).
(c) Amphoteric oxides: These oxides show properties of both acidic oxides and basic oxides. For example, aluminium oxide (Al₂O₃), silicon dioxide (SiO₂).
(d) Neutral oxides: These are neither acidic nor basic and have no effect on litmus paper. For example, water (H₂O).

(i) Detergent solution-Basic solution, gives blue colour with litmus paper.
(ii) Lime water-Basic solution, gives blue colour with litmus paper.
(iii) Soft drinks-Acidic solution, gives red colour with litmus paper.
(iv) Sugar solution-Neutral solution, gives purple colour with litmus paper.
(v)Vinegar-Acidic solution, gives red colour with litmus paper.

(a) Rahul knows that our stomach contains hydrochloric acid. It helps us to digest food. But, too much acid in the stomach causes indigestion. Sometimes, indigestion is painful and some mild base should be taken to relief from this pain. So, this information given by his teacher helped him.
(b) He gave her mother baking soda solution which was available in the kitchen easily. He selects baking soda because it is a mild base and neutralises the excess acid in the stomach and it will give relief from pain.
(c) Rahul is very intelligent and caring boy.

China rose (gudhal) is an acid-base indicator.
China rose solution in different medium shows following changes:
China rose + acid \(\longrightarrow\) Give dark pink colour, hence A is an acidic solution.
China rose + base \(\longrightarrow\) give green colour, hence B is a basic solution.
China rose + neutral \(\longrightarrow\) No change in colour, hence C is a neutral solution.