1.What are olfactory indicators?
(Chapter 2 : Acids, Bases and Salts)

Ans : The substances whose odour changes in acidic or basic media are called olfactory indicators.

2. Acids are sour in taste and change the colour of blue litmus to red.(True/False)
(Chapter 2 : Acids, Bases and Salts)

Ans :True

3. Bases are bitter and change the colour of the red litmus to blue.(True/False)
(Chapter 2 : Acids, Bases and Salts)

Ans :True

4.Name few indicators that helps to test acids/bases.
(Chapter 2 : Acids, Bases and Salts)

Ans:

• Litmus and turmeric are natural indicators.
• Methyl orange and phenolphthalein are synthetic indicators.

5.Name natural indicators to test acids and bases.
(Chapter 2 : Acids, Bases and Salts)

Ans: Litmus, turmeric , red cabbage leaves, coloured petals of flowers like Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a solution.

6.Why does the stain of curry on a white cloth become reddish-brown when washed with soap?
(Chapter 2 : Acids, Bases and Salts)

Ans: Soap is basic in nature and hence the curry stain turns reddish brown when washed.

7.How is the litmus solution prepared?
(Chapter 2 : Acids, Bases and Salts)

Ans: Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to the division Thallophyta, and is commonly used as an indicator. When the litmus solution is neither acidic nor basic, its colour is purple.

8.Explain neutralisation reaction.
(Chapter 2 : Acids, Bases and Salts)

Ans: The reaction between an acid and a base to give salt and water is known as a neutralisation reaction.
The neutralisation reaction can be written as – Base + Acid → Salt + Water

9. Bases which are soluble in water are called _________.
(Chapter 2 : Acids, Bases and Salts)

Ans:alkalies

10. Define an alkali.
(Chapter 2 : Acids, Bases and Salts)

Ans:
An alkali is a base that dissolves in water. They are soapy to touch, bitter and corrosive. Never taste or touch them as they may cause harm.

11.The process of dissolving an acid or a base in water is an _________ reaction.
(Chapter 2 : Acids, Bases and Salts)

Ans: exothermic

12.Why should precaution be taken while mixing concentrated nitric acid or sulphuric acid with water ?
(Chapter 2 : Acids, Bases and Salts)

Ans: If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

13. The p in pH stands for ______ in German, meaning power.
(Chapter 2 : Acids, Bases and Salts)

Ans: potenz

14. A scale used for measuring hydrogen ion concentration in a solution is called _________.
(Chapter 2 : Acids, Bases and Salts)

Ans: pH scale

15. State the compound found in tooth enamel.
(Chapter 2 : Acids, Bases and Salts)

Ans: Tooth enamel is made up of calcium phosphate and is the hardest substance in the body.

16.State the difference between the number of water molecules in Gypsum and Plaster of Paris.
(Chapter 2 : Acids, Bases and Salts)

Ans:
Gypsum : two water molecules.
Plaster of Paris : half a water molecule.