5. Acids, Bases and Salts Class 7 Science Solutions English Medium-NCERT Exercise

Exercise 

Q1. State differences between acids and bases.

Answer:

Acids are sour and turn blue litmus red .Bases are bitter and turn red litmus blue. 

Q2. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

Answer:

Basic.

Q3. Name the source from which litmus solution is obtained. What is the use of this solution?

Answer:

Lichens. It is a used as an indicator.

Q4. Is the distilled water acidic/basic/neutral? How would you verify it?

Answer:

Distilled water is neutral. 

Distilled water has no effect on blue as well as red litmus . So,it is neutral.

Q5. Describe the process of neutralisation with the help of an example.

Answer:

The reaction between an acid and base is known as neutrallisation salt and water are produses in this process with the evolution of heat.

Q6. 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)

Answer:

(i) False (ii) False (iii) True (iv) True (v) False 

Q7. 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?

Answer:

He can decide by the use of drink turns red litmus blue , it is basic. If it turns blue litmus red,it is acidic. If it does not affect litmus,it is neutral

Q8. Explain why:

(a) An antacid tablet is taken when you suffer from acidity. Keywords Acid Acidic Base Basic Indicator Neutral Neutralisation Salt ACIDS, BASES AND SALTS 57

(b) Calamine solution is applied on the skin when an ant bites.

(c) Factory waste is neutralised before disposing it into the water bodies.

Answer:

(a) Antacids tablet are basic in nature so, they neutralise the effect of excess acid in our stomach.

(b) calamine tablets are basic in nature so, they neutralise the effect excess ant bites.

(c) Factory waste contains acid which can harm, water animal and so, it is neutrallised before dispossing it into the water bodies. 

Q9. 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.

Answer:

Samples of the given three liquids are tested by adding a small quantity of turmeric to them. The liquid in which the coiour of turmeric changes from yellow to red ,is a base i.e.,sodium hydroxide solution .Then ,one of them remaining two unidentified solutions is added to it gradually. if the solutions turns yellow again, the added liquid is hydroxide acid.

Q10. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

Answer:

The solution may be neutral or basic. Both types of substance have no effect on blue litmus. 

Q11. 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

Answer:

(iv) only d.