4. Acids, Bases, and Salts

Q1. State differences between acids and bases.

Ans:

Q2. Ammonia is found in many household products, such as window cleaners. What is its nature?

Ans:

Ammonia is basic in nature as it turns red litmus paper blue.

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

Ans:

1. Litmus solution is obtained from lichens, which are a type of plant.
2. The use of litmus solution is as an indicator to test whether a solution is acidic or basic. 

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

Ans:

1. Distilled water is neutral in nature, meaning it is neither acidic nor basic. 
2. To verify this, you can use red or blue litmus paper; it will not change color when dipped in distilled water.

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

Ans:

1. Neutralization is the reaction between equal amounts of an acid & a base.
2. Salt & water are produced in this process with evolution of heat.
3. Acid + Base →  Salt + Water (heat is evolved)
4. Example: When hydrochloric acid reacts with sodium hydroxide, they neutralize each other to produce sodium chloride (table salt) & water. 
5. Equation: HCl + NaOH → NaCl + H₂O

Q6. Mark ‘T’ if the statement is true and ‘F’ if it is false:

Ans:

(i) Nitric acid turns red litmus blue. = F 

(Nitric acid is an acid & turns blue litmus red.)

(ii) Sodium hydroxide turns blue litmus red. = F

(Sodium hydroxide is a base & turns red litmus blue.)

(iii) Sodium hydroxide and hydrochloric acid neutralize 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

(Tooth decay is caused by acids.)

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 an acidic drink, another wants a basic drink. How can Dorji identify the drinks?

Ans:

1. Dorji can identify the drinks by using litmus paper. 
2. If the drink turns blue litmus paper to red, it is acidic.
3. If the drink turns red litmus paper to blue, it is basic.
4. If the drink doesn't change colour of any litmus paper, then it is neutral. 

Q8: Explain why: 

(a) An antacid tablet is taken when you suffer from acidity. 

Ans: 

1. Our stomach contains hydrochloric acid.
2. When this acid becomes excess we suffer from acidity.
3. To neutralize it, we take an antacid tablet which contains milk of magnesia, that is a base.

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

Ans:

1. When an ant bites, it injects an acid (formic acid) into the skin.
2. To neutralize this, calamine solution which contains zinc carbonate which is a base, is applied to the affected area.

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

Ans:

1. Most of the factory waste contain acidic substances which can harm aquatic life if disposed in water.
2. Hence, this waste is neutralized by using a base and then disposed of into water bodies.

Q9. 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.

Ans:

1. To identify the three liquids using turmeric indicator, put a drop of liquid on the indicator.
2. The solution that turns red, is sodium hydroxide, as it is a base.
3. Now, make two mixtures, a drop of sodium hydroxide and other two solutions individually.
4. Add a drop of this solution to the turmeric indicator.
5. The solution that turns red is sugar solution which is neutral.
6. The solution which shows no change is hydrochloric acid which is neutralized by adding sodium hydroxide which is a base.

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

Ans:

1. A base turns red litmus paper blue & no change in blue litmus paper.
2. In neutral solution also blue litmus paper doesn't change.

Hence, the solution can be either basic or neutral.

Q11: Consider the following statements:

(a) Both acids and bases change the color of all indicators.

(b) If an indicator gives a color change with an acid, it does not give a change with a base.

(c) If an indicator changes color with a base, it does not change color with an acid.

(d) Change of color in an acid and a base depends on the type of the indicator.

Which of these statements are correct?

Ans:  only d.