NCERT Solutions for Class 7 – Chapter 5: Acids, Bases and Salts are available here. You can also download Chapter 5: Acids, Bases and Salts of Class 7 Science NCERT textbook with the help of download link given at the end of this article.
Question1. State differences between acids and bases.
Differences between acids and bases are given below
1. Acids turn blue litmus red.
1. Bases turn red litmus blue.
2. Sour in taste.
2. Bitter in taste.
3. Acids give a dark pink colour with China Rose indicator.
3. Bases give a dark green colour with China Rose indicator.
Question2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
The nature of the Ammonia is basic.
Question3. Name the source from which litmus solution is obtained. What is the use of this solution?
Litmus solution is extracted from lichens. It is used as an indicator to distinguish between bases & acids.
Question4. Is the distilled water acidic/basic/neutral? How would you verify it?
Distilled water is neutral and one can easily test it with the help of litmus paper. When we dip litmus paper in neutral water, there will not be any change in the colour.
Question5. Describe the process of neutralisation with the help of an example.
When an acid mixed with a base then they react with each otehr to form the salt with the release of energy and cancel each other's effect. This process is neutralization porcess.
Acid + Base → Salt + Water + Heat
NaOH + HCl → NaCl + H2O + Heat
Question6. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turn red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. (T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
(v) Tooth decay is caused by the presence of a base. (T/F)
(i) Nitric acid turn red litmus blue. (False)
(ii) Sodium hydroxide turns blue litmus red. (False)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (True)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (True)
(v) Tooth decay is caused by the presence of a base. (False)
Question7. 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?
Dorji can use litmus paper to check if the drink is acidic, basic or neutral and can serve the correct drink as per the demand of the customers.
Question8. Explain why:
(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamine solution is applied on the skin when an ant bites.
(c) Factory waste is neutralized before disposing it into the water bodies.
(a) Acidity is caused when an excess of acids is produced in the stomach. An antacid, such as milk of magnesia, act as a base, and react with excess acid and neutralize its effect, thus giving relief.
(b) When an ant bites it basically injects formic acid into the skin. Calamine solution contains zinc carbonate and is basic in nature. When applied in the skin, it reacts with the acid, and neutralizes its effect, thus giving relief.
(c) Most of the factory wastes contain acids. On disposing it directly into the water bodies, it might harm aquatic bodies. Hence, factory waste needed to be neutralized.
Question9. 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.
If we put drops of a base on turmeric, then, the red colour will be obtained. If we mix acid with turmeric, then, there will not be any change in the colour. Here, on mixing turmeric indicator with hydrochloric acid, there will not be a change in the colour. But when we will mix sodium hydroxide, we will get a red colour. The sugar solution is neutral in nature, so mixing it with turmeric indicator will not cause any change in colour.
Question10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
We know acid turns blue litmus to red and neutral solution has no effect on the litmus paper. As there is no change in colour, so, the solution can be either basic or neutral.
Question11. 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 an acid and a base depends on the type of the indicator.
Which of these statements are correct?
(i) All four (ii) a and d (iii) b, c and d (iv) only d
(iv) option is correct.