NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
1. Litmus solution is extracted from lichens.
2. Litmus solution is used as an indicator to find the acidic and basic nature of a solution.
3. It has a mauve (purple) color in distilled water. When added to an acidic solution, it turns red.
When added to a basic solution, it turns blue.
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
1. The reaction between an acid and a base is known as a neutralization reaction.
2. In this reaction, both acid and base cancel each other's effect.
Neutralization reaction results in the formation of salt and water.
3.During this reaction, energy in the form of heat is evolved.
For example:
When sodium hydroxide (NaOH) is added to hydrochloric acid (HCl), sodium chloride (NaCl) and water (H2O) are obtained and heat is evolved.
NaOH + HCl → NaCl + H2O + Heat
Q.6 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turns 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)
(id) 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)
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
(i) Nitric acid turns red litmus blue. (F)
(ii) Sodium hydroxide turns blue litmus red. (F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions.(T)
(v) Tooth decay is caused by the presence of a base.(F)
Q.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?
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
1.
Q.8 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 neutralised before disposing it into the water bodies.
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
(a) Acidity is caused when an excess of acids is produced in the stomach.
The antacid tablet contains base-like milk of magnesia which neutralizes
the acid produced in the stomach, thus giving relief. Hence, it is used while suffering from acidity.
(b) When an ant bites, it injects formic acid into the skin. Calamine solution
contains zinc carbonate which is basic in nature. Therefore, it is applied on the
skin to neutralize the effect of formic acid to bring relief for the affected person.
Hence calamine neutralizes the effect of formic acid.
(c) Factory wastes contain acids. Therefore, these wastes, when thrown
directly to water bodies, harm aquatic lives. Hence, these wastes are
neutralized with basic chemicals before disposing to water bodies.
Q.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.
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
Q.10 Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
1. The solution is basic or neutral in nature.
2. We know acid turns blue litmus to red and neutral solution has no effect on the litmus paper.
As there is no change in color, so, the solution can be either basic or neutral.
Q.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 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) and (c)
(iv) only (d)
NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts
Answer :
(iv) only (d)