NCERT solutions for Science [English] Class 7 chapter 4 - Acids, Bases and Salts [Latest edition]

State the differences between acids and bases.

Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Name the source from which litmus solution is obtained. What is the use of this solution?

Is the distilled water acidic/basic/neutral? How would you verify it?

Describe the process of neutralization with the help of an example.

Nitric acid turns red litmus blue.

Sodium hydroxide turns blue litmus red.

Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water.

Indicator is a substance which shows different colours in acidic and basic solutions. 

Tooth decay is caused by the presence of a base.

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?

Explain why An antacid tablet is taken when you suffer from acidity.

Explain why Calamine solution is applied on the skin when an ant bites.

Explain why factory waste is neutralised before disposing it into the water bodies.

Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and the third is a sugar solution. How will you identify them? You have only turmeric indicator.

Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

1. Both acids and bases change colour of all indicators.
2. If an indicator gives a colour change with an acid, it does not give a change with a base.
3. If an indicator changes colour with a base, it does not change colour with an acid.
4. Change of colour in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

Using the knowledge of acids and bases, write a secret message with the help of baking soda and beet root. Explain how it works.

(Hint: Prepare baking soda solution in water. Use this solution to write the message on a sheet of white paper with a cotton bud. Rub a slice of fresh beetroot over the message.)

Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and basic solutions with it. Present your observations in the form of a table.

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.

Visit a doctor. Find out the medicines, he prescribes to treat acidity. Ask him how acidity can be prevented.