NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts
Class 7 Science Chapter 5 Acids, Bases and Salts for cbse/icse students
Question 1. State differences between acids and bases.
- Bases are bitter to taste while acids are sour.
- Litmus turns blue when acid is present while Bases turn red litmus blue.
- A substance that contains hydrogen ions is called an acid. Bases are substances that contain hydroxyl ions
Question 2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Ans: Ammonia is a basic substance.
Question 3. Name the source from which litmus solution is obtained. What is the use of this solution?
Ans: Lichen ( association of algae and fungi) is used to extract litmus solution. It determines whether a given solution is acidic or basic.
Question 4. Is the distilled water acidic, basic, or neutral? How would you verify it?
Ans: Distilled water is neutral. As we can see, neither blue nor red litmus paper changes color when dipped in them.
Question 5. Describe the process of neutralization with the help of an example.
Ans: A neutralization reaction occurs when an acid reacts with a base to form salt and water. For example,
HCL + NAOH = NACL + H2O
Question 6. Mark ‘T’ if the statement is true and ‘F’ if it is false:
- Nitric acid turns red litmus blue. (T/F)
- Sodium hydroxide turns blue litmus red. (T/F)
- Sodium hydroxide and hydrochloric acid neutralize each other and form salt and water. (T/F)
- Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
- Tooth decay is caused by the presence of a base. (T/F)
Question 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 a neutral drink. How will Dorji decide which drink is to be served to whom?
Ans: An indicator can help him decide. It is basic if the sample of drink turns red litmus blue. It turns blue litmus red if it is acidic. It is neutral if it does not affect litmus.
Question 8.Explain why :
(a) An antacid tablet is taken when you suffer from acidity.
Ans: We take an antacid such as milk of magnesia to treat indigestion. It has the ability to neutralize acidic effects.
(b) Calamine solution is applied on the skin when an ant bites.
Ans: All ants inject acidic liquid in human skin when they bite. Inflammation of the skin is caused by this acidic liquid, which is formic acid. Calamine solution, which contains zinc carbonate, can be used to neutralize the sting. Zinc carbonate is a weak base and does not harm the skin.
(c) Factory waste is neutralized before disposing it into the water bodies.
Ans: Many factories produce acidic wastes. Acids will kill fish and other aquatic organisms if allowed to flow into water bodies without being neutralized properly. Therefore, factory wastes need to be neutralized by adding a few basic substances to them before they can be dumped into water bodies.
Question 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 a turmeric indicators.
Ans: Hydrochloric acid – Turmeric’s yellow color turns blue
Sodium hydroxide – Color of turmeric changes to red
Sugar solution – No change
Question 10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Ans: Solution may be neutral or basic. Blue litmus is unaffected by either type of substance. You can test the color of this solution by putting a drop on a red litmus paper. IF the solution turns blue, then it’s a basic solution, and if no color change occurs, then it’s a neutral solution.
Question 11. Consider the following statements:
(a) Both acids and bases change colour of all indicators.
(b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in acid, and a base depends on the type of the indicator.
Which of these statements are correct?