Students can Download Science Chapter 5 Acids, Bases and Salts Questions and Answers, Notes Pdf, KSEEB Solutions for Class 7 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.
Karnataka State Syllabus Class 7 Science Chapter 5 Acids, Bases and Salts
Class 7 Science Acids, Bases and Salts Textbook Exercise Questions and Answers
Question 1.
State differences between acids and bases.
Answer:
| Acids | Bases |
| (a) Acids are sour to taste. | Bases are bitter to taste. |
| (b) Acids turn blue litmus to red. | Bases turn red litmus to blue. |
Question 2.
Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Answer:
Ammonia turns red litmus blue. Hence, it is basic in nature.
Question 3.
Name the source from which litmus solution is obtained. What is the use of this solution?
Answer:
Litmus solution is obtained from lichens. A natural dye extracted from lichens is dissolved in distilled water to obtain litmus solution. It is used as an indicator to distinguish between acids and bases.
Question 4.
Is the distilled water acidic/basic/ neutral? How would you verify it?
Answer:
Distilled water is neutral in nature. This can be verified by using red or blue litmus papers. Distilled water will not change the colour of any of the litmus papers.
Question 5.
Describe the process of neutralization with the help of an example.
Answer:
Neutralization: It is the reaction between an acid and a base to produce salt and water along with heat.
Acid + Base → Salt + Water (Heat is evolved).
Example:
Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) base and forms sodium chloride (NaCl) salt and water (H2O).
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H2O)
Question 6.
Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Nitric acid turns red litmus blue. (T/F)
(b) Sodium hydroxide turns blue litmus red. (T/F)
(c) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
(d) The indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
(e) Tooth decay is caused by the presence of a base. (T/F)
Answer:
(a)-F;
(b)-F;
(c)-T;
(d)-T;
(e)-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 an acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Answer:
Dorj can decide testing the solutions in the following ways:
- By tasting: Acidic drink tastes sour. Basic drink tastes bitter. Neutral drink wall not have above taste.
- By testing with litmus paper: Acidic drink turns blue litmus red. Basic drink turns red litmus blue. Neutral drink does not show any colour change in indicator.
Question 8.
Explain why:
(a) An antacid tablet is taken when you suffer from acidity
Answer:
Indigestion in the stomach causes acidity. An antacid contains a base like magnesium hydroxide which neutralise the effect of excessive acid in our stomach.
(b) Calamine solution is applied on the skin when an ant bites.
Answer:
Ant bite injects formic acid into the skin. Calamine solution contains zinc carbonate which neutralises the effect of acid when applied on the skin.
(c) Factory waste is neutralised before disposing it into the water bodies.
Answer:
Factory waste contains acids. These are neutralised by adding basic substances before disposing into water bodies to protect the aquatic animals and plants.
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 turmeric indicator.
Answer:
The following steps are taken to test the given liquids:
(a) Add a drop of each liquid on turmeric powder. The solution which changes the colour of the indicator to red is a base, i.e., sodium hydroxide.
(b) Turmeric retains its yellow colour in acidic and neutral medium. Hence put a drop of sodium hydroxide on the other two liquids separately and add them on the turmeric indicator. The mixture that changes the colour of the indicator red contains a neutral sugar solution. The mixture does not become warm. While the mixture which does not show any colour change and becomes warm contains hydrochloric acid. The acid was neutralised on the addition of sodium hydroxide.
Question 10.
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
Answer:
The above solution could be a base or a neutral solution because:
- Bases turn red litmus to blue but do not react with blue litmus.
- Neutral substance also does not react with a litmus solution.
Question 11.
Consider the following statements:
(a) Both acids and bases change the 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).
Answer:
(iv) Only (d).