Chapter 4
Acids, Bases and Salts
1. State differences between acids and bases.
Ans: Acid is a kind of chemical compound that when dissolved in water gives a solution with H+ ion activity more than purified water. A base is an aqueous substance that donates electrons, accepts protons or releases hydroxide (OH-) ions. An acid is a proton donor.
2. Ammonia is found in many household products, such as window
cleaners. It turns red litmus blue. What is its nature?
Ans: basic in nature.
3. Name the source from which litmus solution is obtained. What is the
use of this solution?
Ans: litmus solution is obtained from lichens and it is used in predicting the nature of the solution i.e. acid or base.
4. Is the distilled water acidic/basic/neutral? How would you verify it?
Ans: neutral.
5. Describe the process of neutralisation with the help of an example
Ans: Neutralisation Reaction. When a strong acid reacts with a strong base the resultant salt is neither acidic nor basic in nature i.e. it is neutral. For example when HCl (Hydrochloric acid), a strong acid, reacts with NaOH, a strong base, the resulting salt is sodium chloride and water.
6. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turn red litmus blue. (T/F)
Ans: False .
(ii) Sodium hydroxide turns blue litmus red. (T/F)
Ans: False.
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and
form salt and water. (T/F)
Ans: False.
(iv) Indicator is a substance which shows different colours in acidic
and basic solutions. (T/F)
Ans: true.
v) Tooth decay is caused by the presence of a base. (T/F)
Ans: False.
7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Ans: Dorji can use a handy tool called litmus paper to identify the acidity or alkalinity (basicity) of the unlabeled drinks. Here's how it works:
- Litmus paper comes in two types: red and blue.
- For acidic drinks: If Dorji dips a piece of blue litmus paper into a drink and it turns red, that drink is acidic.
- For basic drinks: If he dips a piece of red litmus paper into a drink and it turns blue, that drink is basic.
- For neutral drinks: If there's no color change on either red or blue litmus paper, then the drink is considered neutral (with a pH of 7).
By using litmus paper on each drink, Dorji can easily identify the acidic, basic, and neutral drinks to fulfill his customers' requests.
8. Explain why:
(a) An antacid tablet is taken when you suffer from acidity.
Ans: That's absolutely correct! Antacid tablets are specifically designed to help relieve discomfort caused by excess stomach acid. They work by neutralizing the acid in your stomach, providing relief from heartburn, indigestion, and sour stomach.
(b) Calamine solution is applied on the skin when an ant bites
Ans: When an ant bites, it injects an acidic liquid (formic acid) into the skin. Calamine solution contains zinc carbonate, which is basic in nature and neutralises the effect of acid injected by the ant. That's why it is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water
bodies.
Ans: Factory wastes contain chemicals and harmful acids which may be harmful to the aquatic life and also lead to pollution of water. That's why factory waste is neutralised before disposing it into the water bodies.
9. Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.
Ans: The turmeric in the sugar solution will turn red upon addition of sodium hydroxide as the solution will turn basic. Whereas the turmeric in the hydrochloric solution will undergo no change as the solution will become neutral upon addition of the base and turmeric is yellow in acidic as well as
10. Blue litmus paper is dipped in a solution. It remains blue. What is the 10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Ans: Basic and neutral solutions do not have any effect on blue litmus paper. Only acidic solution can change the colour of blue litmus paper to red. So, the solution can be basic or neutral.
11. Consider the following statements:
(a) Both acids and bases change colour of all indicators.
Ans:
(b) If an indicator gives a colour change with an acid, it does not give a
change with a base.
Ans:
(c) If an indicator changes colour with a base, it does not change colour
with an acid.
Ans:
Which of these statements are correct?
(i) All four (ii) a and d (iii) b, c and d (iv) only d
1. Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet root. Explain how it works.
Ans: Baking soda is a base, while beetroot is acidic. The anthocyanin pigment in the beetroot reacts with the alkaline baking soda, causing a color change. The hidden message written with the baking soda solution will start to appear on the paper as a result of the chemical reaction.
3. Bring the soil sample of your area, find out if it is acidic, basic or neutral. Discuss with farmers if they treat the soil in any manner.
Ans: We can check that soil is acid basic or salt by mixing little amount of water with soil in a beaker. After that we have to put an universal indicator in the beaker. They usually treat with calcium chalk or slaked lime when the soil becomes too acidic to neutrilize it.
4. Visit a doctor. Find out the medicines, he prescribes to treat acidity. Ask him how acidity can be prevented.
