Chapter 12 - Introduction to Acid & Base
1. Identify the following solutions, whether they are acid or base.
| Sol | Change in Indicator | Acid / Base | ||
|---|---|---|---|---|
Litmus | Phenolphthalein | Methyl orange | ||
1. | — | No change | — | |
2. | — | — | Orange colour turns red | |
3. | Red litmus turns blue | — | — | |
Ans:
| Sol | Change in Indicator | Acid / Base | ||
|---|---|---|---|---|
Litmus | Phenolphthalein | Methyl orange | ||
1. | Blue litmus turns red | No change | Orange colour turns red | Acid |
2. | Red litmus turns blue | No change | Orange colour turns red | Acid |
3. | Red litmus turns blue | Colourless solution turns pink | Yellow | Alkali |
2. Write chemical names from given formulae.
a. H₂SO₄
Ans: Sulphuric acid
b. Ca(OH)₂
Ans: Calcium hydroxide
c. HCl
Ans: Hydrochloric acid
d. NaOH
Ans: Sodium hydroxide
e. KOH
Ans: Potassium hydroxide
f. NH₄OH
Ans: Ammonium hydroxide
3. Sulphuric acid has highest importance in chemical Industry. Why?
Ans:
(i) Sulphuric acid (H₂SO₄) is used in the manufacture of a number of other chemicals. It is used in making fertilizers, detergents, pigments, medicines, insecticides, explosives, etc.
(ii) It is used in the pulp and paper industry, glass making, soap making, dyeing, etc.
(iii) Diluted sulphuric acid is used in the batteries (electric cells).
(iv) It is used in the iron and steel industry to remove rust from products.
(v) Sulphuric acid is referred to as the “king of chemicals” due to its numerous applications. Thus, sulphuric acid has the highest importance in the chemical industry.
4. Give answers.
a. Which acid is used for getting chloride salt?
Ans: Hydrochloric Acid (HCl) is used for getting chloride salt.
b. By squeezing lemon on a piece of rock the gas liberated turned lime water milky. Which compound is present in the rock?
Ans: The compound present in the rock is metal carbonate.
c. The label on the bottle of chemical is spoiled. How will you find whether the chemical is acidic or not?
Ans:
(i) We can identify whether the chemical is acidic or not by using indicators such as litmus paper.
(ii) If the chemical turns blue litmus red, it is acidic, and if it turns red litmus blue, it is basic. Thus, based on the colour change of the indicator, we can find out whether the chemical is acidic or not.
5. Answer the following questions.
a. Explain the difference between acid and base.
Ans:
| Acids | Alkalies |
|---|---|
(i) Acids are sour to taste. | (i) Alkalies are bitter to taste. |
(ii) Acid molecules contain hydrogen ions (H⁺) as their main constituent. | (ii) Alkali molecules contain the hydroxide ion (OH⁻) as their main constituent. |
(iii) Acids turn blue litmus paper red. | (iii) Alkalies turn red litmus paper blue. |
(iv) Nonmetal oxides are generally acidic in nature. | (iv) Metal oxides are generally alkaline in nature. |
For example: HCl, H₂SO₄ | For example: NaOH, Mg(OH)₂, etc. |
b. Why indicator does not get affected by salt?
Ans:
(i) Indicators change colour in the presence of acid or alkali.
(ii) Common salt (sodium chloride) is formed by the combination of acid (hydrochloric acid) and alkali (sodium hydroxide). This chemical reaction is called a neutralization reaction.
(iii) As a result, common salt is naturally neutral, meaning it is neither acidic nor alkaline.
Hence, indicators do not get affected by common salt.
c. Which substances are produced by neutralization process ?
Ans: In the neutralization process, acid and alkali combine to produce salt and water.
d. Which are the industrial uses of acids?
Ans: Industrial uses of acids include:
(i) Acids are used in the manufacturing of chemical fertilizers.
(ii) Acids are used in the manufacture of explosives, oil purification, medicines, dyes, and paints.
(iii) Hydrochloric acid (HCI) is used in preparing different chloride salts.
(iv) Dilute sulphuric acid (H₂SO₄) is used in the batteries (electric cells).
(v) Dilute HCI is used for sterilisation of water.
(vi) Acid is used for making white paper from wood pulp.
6. Select the proper word given in bracket and fill in the blanks.
a. Main constituent of acid is………..
Ans: hydrogen (H⁺) ion
b. Main constituent of the base is…….
Ans: hydroxide (OH⁻) ion
c. Tartaric acid is a …………. acid.
Ans: natural (organic)
7. Match the pairs.
| Group A | Group B |
|---|---|
1. Tamarind | a. Acetic acid |
2. Curd | b. Citric acid |
3. Lemon | c. Tartaric acid |
4. Vinegar | d. Lactic acid |
Ans:
| Group A | Group B |
|---|---|
1. Tamarind | c. Tartaric acid |
2. Curd | d. Lactic acid |
3. Lemon | b. Citric acid |
4. Vinegar | a. Acetic acid |
8. State true or false.
a. Oxides of metals are acidic in nature.
Ans: True
b. Table salt is acidic.
Ans: False
Common salt (NaCl) is neutral.
c. Metal corrodes due to salts
Ans: False
Metal corrodes due to water, oxygen or other gases. The process of corrosion accelerates in presence of salt, acid or base.
d. Salts are neutral.
Ans: False
All salts are not neutral. Some salts can be acidic or basic.
9. Classify following substances into acidic, basic and neutral group –
HCl, NaCl, MgO, KCl, CaO, H₂SO₄, HNO₃, H₂O, Na₂CO₃
Ans:
| Acidic | Basic | Neutral |
|---|---|---|
HCl | MgO | NaCl |
H₂SO₄ | CaO | KCl |
HNO₃ | Na₂CO₃ | H₂O |