Question

D. Answer in one or two sentences.

1. Write down the uses of acids.

2. What are antacids? Give some examples.

3. What do you understand by neutralisation?

4. What are indicators? Name some indicators and their effects on acids and bases.

5. Differentiate between acids and bases.

6. How does a salt react with (a) an acid (b) a base?

7. How will you identify whether a substance is an acid or a base? (i) By using litmus paper (ii) At home, if you don't have a litmus paper.

8. How does a farmer maintain the balance of acidic character of soil?​

Answer 1

physical substance in general, as distinct from mind and spirit; (in physics) that which occupies space and possesses rest mass, especially as distinct from energy.

Answer 2

1 )

benzoic acid: salt used to preserve food

Ethanoic acid: used to clean metals before electroplating/processing leather/household cleaning/ maintenance of swimming pools Nitric acid:used in the production of fertilizers, explosives, dissolution of metals-extractiona and purification of gold

2 )

An antacid is a substance which neutralizes stomach acidity

Examples:

Aluminum hydroxide gel (Alternagel, Amphojel)

Calcium carbonate (Alka-Seltzer, Tums)

Magnesium hydroxide (Milk of Magnesia)

3 )

A reaction in which an acid and base react with

each other to give a salt and water is termed as neutralisation. In this reaction, energy is evolved in the form of heat.

4 )

Indicators are substances that show a change in at least one of their properties(like colour or smell) when brought in contact with acids and bases. These indicators indicate the nature of a substance by this change.

Names of indicators: Litmus, turmeric.

Effects of indicators on acids and bases:

• Acids turn blue litmus red and bases turn red litmus blue.

• Bases mixed in a solution of turmeric powder

give red colour. Turmeric solution does not change its colour with acid.

5 )

ACIDS

• An acid is a molecule or substance that has a pH value less than 7.

• As per Arrhenius Concept, an acid elevates the concentration of Hydrogen ions when dissolved in water.

• In the Bronsted-Lowry Concept, acids are substances which donate protons

BASES

• A base (alkaline) is a molecule or substance that has a pH value higher than 7.

• As per Arrhenius Concept, a base is a compound that increases the concentration of hydroxide ions (OH–) when dissolved in water

• Bases, on the other hand, are substances which accept protons

6 ) ( a )

acid + hydrogencarbonate → salt + water + carbon dioxide

Observations: solid white sodium hydrogencarbonate disappears, colourless solution produced, bubbles. The carbon dioxide gas produced in these reactions can be tested.

( b )

Salt, in chemistry, substance produced by the reaction of an acid with a base. A salt consists of the positive ion (cation) of a base and the negative ion (anion) of an acid.

7 ) ( i )

The main use of litmus is to test whether a solution is acidic or basic. Light-blue litmus paper turns red under acidic conditions, and red litmus paper turns blue under basic or alkaline conditions.

( ii )

In the absence of litmus paper, a reagent phenolphthalein can be used. The solution which develops pink colour with phenolphthalein is a base and the other is acid.