Acids, Bases and Salts for Class 10th
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Chemistry
Chapter 2
Acids, Bases and Salts
Chapter Notes
Top concepts:
1.Methyl orange: Methyl orange turns pink in acids and becomes yellow in bases.
2. On the basis of origin, acids are classified as:
a. Organic acids: Acids derived from living organisms like plants and animals are called organic acids. They are weak acids and are not harmful for living organisms. For example: citric acid is present in fruits, acetic acid present in vinegar, oxalic acid present in tomato, tartaric acid present in tamarind, lactic acid present in sour milk and curd.
b. Mineral acids: They are also called inorganic acids. They are dangerous and corrosive. Special precautions have to be taken while handling them. For example: sulphuric acid (H2SO4), hydrochloric acid (HCl) etc.
3. On the basis of their strength, acids are classified as:
a. Strong acids: Strong acids are those acids which completely dissociate into its ions in aqueous solutions. Example: nitric acid (HNO3) , sulphuric acid(H2SO4), hydrochloric acid(HCl)
b. Weak acids: Weak acids are those acids which do not completely dissociate into its ions in aqueous solutions. For example: carbonic acid (H2CO3), acetic acid (CH3COOH)
4. On the basis of their concentration, acids are classified as:
a. Dilute acids: Have a low concentration of acids in aqueous solutions.
b. Concentrated acids: Have a high concentration of acids in aqueous solutions.
5. Alkalies: Water soluble bases are called alkalies. For example: Sodium hydroxide (NaOH), potassium hydroxide(KOH)
6. On the basis of their strength, bases are classified as:
a. Strong bases: Strong bases are those bases which completely dissociate into its ions in aqueous solutions. Example: sodium hydroxide (NaOH), potassium hydroxide (KOH)
b. Weak bases: Weak bases are those bases which do not completely dissociate into its ions in aqueous solutions. For example: ammonium hydroxide (NH4OH)
7. On the basis of their concentration, bases are classified as:
a. Dilute bases: Have a low concentration of alkali in aqueous solutions.
b. Concentrated bases: Have a high concentration of alkali in aqueous solutions.
8. Acids and bases conduct electricity because they produce ions in water. There is a flow of electric current through the solution by ions.
9. Indicators are those chemical substances which behave differently in acidic and basic medium and help in determining the chemical nature of the substance. Acid base indicators indicate the presence of an acid or a base by a change in their colour or smell.
10.Indicators can be natural or synthetic.
11.Olfactory indicators: These are those indicators whose odour changes in acidic or basic medium. Example: onion
12.Onion: Smell of onion diminishes in a base and remains as it is in an acid.
13.Vanilla essence: The odour of vanilla essence disappears when it is added to a base. The odour of vanilla essence persists when it is added to an acid.
14.Turmeric: In acids, yellow colour of turmeric remains yellow. In bases, yellow colour of turmeric turns red.
15.Litmus: Litmus is a natural indicator. Litmus solution is a purple dye which is extracted from lichen. Acids turn blue litmus red. Bases turn red litmus blue. Water is essential for acids and bases to change the colour of litmus paper. Remember that litmus paper will act as an indicator only if either the litmus paper is moist or the acid or base is in the form of aqueous solution. This is because acids and bases release H+ and OH- ions respectively in aqueous solutions.
16.Phenolphthalein: Phenolphthalein remains colourless in acids but turn pink in bases.
Some Important Questions of this Chapter
1. What are the symptoms of the problem of acidity? What possible remedy can be used at home?
2. Name three chemical indicators.
3. How does turmeric change its colour in an alkaline medium?
4. Write equations for the reaction of an acid with;
(a) a metal (b) a metal carbonate (c) a metal hydrogencarbonate (d) a base (e) a metallic oxide.
5. On keeping curd in a brass vessel for sometime, it becomes bitter. Why?
6. What happens when an acid is dissolved in water?
7. Why is HCl gas unable to change the colour of a dry blue litmus paper? What happens if the litmus paper is moistened?
8. A solution of HCl in water conducts electricity but that of glucose in water does not. Why?
9. What is a hydronium ion? How is it formed?
10. Which ions are generated by bases in water?
11. For diluting an acid, the acid should be poured carefully in water and not the reverse. Why?
12. When an acid is mixed with water, what happens to:-
(a) The conc. of hydronium ions per unit volume. (b) The conc. of hydroxide ions per unit volume.
13. Two solutions A & B have pH 2 and 6 respectively. Which is more acidic?
14. Name the hardest chemical substance present in our body.
15. How does acid rain water affect the survival of aquatic life?
16. Why does bee-sting cause pain and irritation? What relief can be given in such a case immediately?
17. From the following, pick the acidic, basic or neutral salts:- (a) Sodium chloride (b) Sodium acetate (c) Ammonium chloride (d) Calcium carbonate (e) sodium carbonate
18. What is chlor-alkali process?
19. How is baking soda & washing soda manufactured?
20. Explain the role of baking soda in baking powder.
21. What is meant by water of crystallization?
22. How can you show with an activity the presence of water in blue copper Sulphate crystals?
23. How is gypsum different from plaster of paris chemically?
24. Why should POP be stored in air tight containers?
25. Write 2 uses of: Washing soda, baking soda. bleaching powder.
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