Science 2 Marks Questions

China rose (gudhal) is an acid-base indicator which shows the following changes in different mediums.
China rose + acid → Give dark pink colour
China rose + base → Give green colour
China rose + neutral → No change in colour
They got variation in their results because solution 'A' was acidic, solution 'B' was basic and solution 'C' was neutral which gave different results with China rose indicator.

We can get solid sodium chloride by evaporation method. It is the process by which water changes from a liquid to a gas or vapour by heating the solution.
Rate of evaporation increases with temperature.

(i) If the wastes of a factory flow into waterbodies, it can cause a threat to the lives of sea creatures. Thus, fish were dying because factory waste may contain acids or bases or other toxic materials.
(ii) If the factory waste is acidic in nature, it can be neutralised by adding basic substances.

No, because orange juice is acidic in nature. Excess of acid in her stomach can increase indigestion. She should take an antacid such as milk of magnesia which contains magnesium hydroxide to neutralise the excess acid.

Wasp sting inject a liquid in the skin which is acidic in nature. Hence, baking soda is the appropriate remedy as it is basic in nature and neutralises the acid.

Nature of solution is given below

Test tube	Nature of solution	Change in colour of red litmus
A	Neutral	No change
B	Basic	Turn blue
C	Acidic	No change
D	Neutral	No change

A small amount of hydrochloric acid produced in the stomach is useful as it can kill the harmful bacteria that may enter into the stomach along with the food. However, if excess of acid is produced, there is a burning sensation in the stomach. We should take milk of magnesia as an antacid medicine to neutralise the excess acid.

The reaction in which an acid reacts with a base to form salt and water is called neutralisation. Acids and bases are chemically opposite substances. So, when an acid is mixed with a base, they neutralise (or cancel) the effect of each other. In this process, both the acidic nature of acid and basic nature of base are destroyed.
The solution formed is neutral, but salt produced during the reaction can be acidic, basic or neutral.
Some heat is always evolved, during the reaction, which raises the temperature of the mixture.
The general reaction takes place is given as
Acid + Base → Salt + Water (Heat is evolved)
This can be understand by following example

The reason for low crop yield in farmer's field was that the soil at a place is either too acidic or too basic. The soil may be acidic or basic naturally. The excessive use of fertilisers in the fields also makes the soil too acidic. In this case, it is treated with base such as quicklime (calcium oxide) or slaked lime (calcium hydroxide) which neutralises the excess acid present in the soil and reduces its acidic nature.
If the soil is too basic, then decaying organic matter (called manure or compost) is added to it. The decaying organic matter releases acid which neutralises the excess bases present in the soil and reduces its basic nature.

The neutralisation reactions play a very important role in our everyday life. Some of the examples that involves neutralisation reaction are as follows
Indigestion
Our stomach produces Hydrochloric Acid (HCl) which helps in digesting the food present in it. Sometimes, excess of hydrochloric acid causes indigestion. It can lead to pain and irritation in the stomach.
To relieve indigestion, we take an antacid which contains bases, e.g. milk of magnesia has magnesium hydroxide. It neutralises the excess acid present in the stomach and cures indigestion.
Ant Bite
When an ant bites, it injects an acidic liquid into the skin of the person which causes burning sensation. The sting of an ant contains an acid called formic acid.
The effect of the acid can be neutralised by rubbing a mild base, e.g. baking soda solution (sodium hydrogen carbonate) or calamine solution which contains zinc carbonate.
Thus, being a base, baking soda solution or calamine solution neutralises the acidic liquid injected by the ant and cancel its effect.

In neutralisation reaction, heat is always evolved which raises the temperature of the reaction mixture. Therefore, if we touch the test tube immediately after the neutralisation reaction, it is found to be hot.
Acid + Base → Salt + Water (heat is evolved)

Acid can be tested in any substance by the following methods
(i) Take a drop of the dilute solution of the substance on the tips of your tongue. If tastes sour, it is acidic.
(ii) Dip a blue litmus paper in the solution. If the colour of the litmus paper turns red, the solution is acidic.

Characteristics of acids are
(i) They are sour in taste.
(ii) They turn blue litmus paper/solution to red.
(iii) They react with bases to form salt and water.

(A) Only (iv)
All indicators do not change colour with acids as well as bases, e.g. turmeric changes its colour to pink with base, but it remains yellow with acid. Therefore, statement (i) is incorrect.
There are some indicators which changes colour with both acid and base, e.g. methyl orange, litmus, thus statement (ii) and (iii) are also incorrect. Change of colour with an acid and a base depends on the type of the indicator used. Hence, only statement (iv) is correct.

We will put a drop each of hydrochloric acid, sodium hydroxide and sugar solution on the turmeric indicator one by one. The liquid which changes the colour of turmeric indicator to red is basic in nature that is sodium hydroxide.
Now, this red turmeric paper may be used to identify which one of the remaining two liquids is hydrochloric acid. Put one drop of each of these remaining liquid on the red turmeric paper. The liquid whose drop will turn this red paper to yellow is hydrochloric acid. This is because hydrochloric acid neutralised the effect of sodium hydroxide on turmeric paper. There is no effect on turmeric solution by sugar solution as it is a neutral solution.

The neutralisation reactions play a very important role in our everyday life.
Some of the examples that involves neutralisation reaction are as follows
Indigestion
Our stomach produces Hydrochloric Acid (HCl) which helps in digesting the food present in it. Sometimes, excess of hydrochloric acid causes indigestion. It can lead to pain and irritation in the stomach.
Ant Bite
When an ant bites, it injects an acidic liquid into the skin of the person which causes burning sensation. The sting of an ant contains an acid called formic acid.

Differences between acids and bases are as follows

Acids	Bases
They are sour in taste.	They are bitter in taste.
They turn blue litmus to red.	They turn red litmus to blue.
They are not soapy to touch.	They are soapy to touch.
They are soluble in water.	They may or may not be soluble in water.

The acid used in the making of paneer at home is citric acid or lactic acid, which is present in lemon juice or curd.