CBSE Class 10 Science Acids Bases And Salts Worksheet Set 07

This second printable worksheet for Class 10 Science Chapter 2, Acids, Bases and Salts, contains 24 questions with answers on matching, definitions, classification of acids and bases, water of crystallisation, natural acids and uses of common compounds. It is arranged to print on a page or two for quick revision before a test.

Matching Questions

Question 1. Match: P. Mg(OH)₂, Q. CaSO₄·½H₂O, R. CaSO₄·2H₂O, S. CaOCl₂ with 1. Plaster of Paris (POP), 2. Gypsum, 3. Bleaching Powder, 4. Milk of magnesia.
Answer:
P - 4: Mg(OH)₂ is milk of magnesia
Q - 1: CaSO₄·½H₂O is Plaster of Paris
R - 2: CaSO₄·2H₂O is gypsum
S - 3: CaOCl₂ is bleaching powder
In simple words: Common names and formulae.

Teacher's Note:
1. POP has half a water molecule.
2. Gypsum has two.

Question 2. Match the uses: P. Manufacture of antacid, Q. Preservation of food, R. Manufacturing of soap, S. Used in automobile batteries with 1. NaOH, 2. H₂SO₄, 3. NaHCO₃, 4. CH₃COOH.
Answer:
P - 3: antacids contain NaHCO₃
Q - 4: CH₃COOH (vinegar) is a preservative
R - 1: soap is made with NaOH
S - 2: car batteries use H₂SO₄
In simple words: Match each compound with its use.

Teacher's Note:
1. Vinegar preserves pickles.
2. Sulphuric acid is used in car batteries.

Very Short Answer Questions

Question 3. How do we identify acids?
Answer:
Acids turn blue litmus red and are sour in taste. They give H⁺ ions in water, react with metals to give hydrogen, and react with carbonates and hydrogencarbonates to give carbon dioxide (effervescence).
In simple words: Acids turn blue litmus red and give H⁺ ions.

Teacher's Note:
1. Never taste unknown chemicals in the laboratory.
2. Give at least two tests.

Question 4. What do you mean by the family of salts?
Answer:
Salts having the same positive ion (radical) or the same negative ion (radical) belong to the same family. For example, NaCl and Na₂SO₄ belong to the sodium family; NaCl and KCl belong to the chloride family.
In simple words: Salts with a common ion form a family.

Teacher's Note:
1. NCERT gives this in the topic on salts.
2. Give two examples.

Question 5. What is efflorescence? Give an example.
Answer:
Efflorescence is the loss of water of crystallisation by a hydrated salt on exposure to air. Example: washing soda crystals turn into a white powder, Na₂CO₃·10H₂O → Na₂CO₃·H₂O + 9H₂O.
In simple words: Hydrated crystals that lose water in air show efflorescence.

Teacher's Note:
1. Do not confuse with deliquescence, which is absorption of water.
2. Washing soda is the common example.

Question 6. What are alkalies? Give example of an alkali.
Answer:
Bases that are soluble in water are called alkalis. Example: sodium hydroxide, NaOH, or potassium hydroxide, KOH.
In simple words: Alkalis are water-soluble bases.

Teacher's Note:
1. All alkalis are bases but not all bases are alkalis.
2. Give one named example.

Question 7. Which of these vanilla, onion and clove can be used as olfactory indicator?
Answer:
All three (vanilla essence, onion and clove oil) can be used as olfactory indicators, because their smell changes in a basic medium.
In simple words: All three lose their smell in a base.

Teacher's Note:
1. Olfactory means related to smell.
2. Test them with dilute NaOH.

Question 8. Name a natural antidote of nettle sting.
Answer:
The dock plant, which grows near nettle plants. Its leaves are rubbed on the stung area.
In simple words: Dock plant leaves relieve nettle sting.

Teacher's Note:
1. Nettle injects formic acid.
2. Baking soda is a chemical antidote.

Question 9. Why is HCl a stronger acid than acetic acid?
Answer:
HCl ionises completely in water and gives a larger concentration of H⁺ ions than acetic acid of the same concentration, which ionises only slightly.
In simple words: HCl gives more H⁺ ions.

Teacher's Note:
1. Strength depends on ionisation.
2. Compare with universal indicator colours.

Question 10. Which acid is produced in stomach?
Answer:
Hydrochloric acid (HCl) is produced in the stomach. It helps in the digestion of food.
In simple words: The stomach makes HCl.

Teacher's Note:
1. Excess acid causes acidity.
2. Antacids neutralise it.

Question 11. Name a salt which does not contain water of crystallisation.
Answer:
Sodium chloride (common salt), or baking soda, NaHCO₃.
In simple words: Not all salts have water of crystallisation.

Teacher's Note:
1. Anhydrous salts have no water in their crystals.
2. Give a named salt.

Question 12. State the purpose for which universal indicator is used.
Answer:
A universal indicator is used to find the approximate pH of a solution, and so to know whether it is acidic, basic or neutral and how strong it is.
In simple words: Universal indicator tells the pH.

Teacher's Note:
1. It is a mixture of indicators.
2. Colour chart gives pH.

Question 13. What happens when water is added to quick lime?
Answer:
Quick lime reacts with water vigorously and a lot of heat is evolved. Slaked lime is formed: CaO + H₂O → Ca(OH)₂ + heat.
In simple words: Quick lime plus water gives slaked lime and heat.

Teacher's Note:
1. The reaction is exothermic.
2. Slaked lime is calcium hydroxide.

Question 14. List two examples of salts which are obtained from strong acid and strong base.
Answer:
Sodium chloride (NaCl) and sodium sulphate (Na₂SO₄) (also potassium sulphate).
In simple words: Such salts are neutral.

Teacher's Note:
1. Their solutions have pH 7.
2. Name the acid and the base.

Question 15. List two examples of salts which are obtained from weak acid and weak base.
Answer:
Ammonium acetate (CH₃COONH₄) and ammonium carbonate ((NH₄)2CO₃).
In simple words: Weak acid + weak base gives these salts.

Teacher's Note:
1. Ammonium salts of weak acids are examples.
2. Strong acid + strong base gives a neutral salt; strong acid + weak base gives an acidic salt; weak acid + strong base gives a basic salt.

Question 16. List two examples of salts which do not contain metal ions.
Answer:
Ammonium chloride (NH₄Cl) and ammonium acetate (CH₃COONH₄) or ammonium carbonate.
In simple words: Ammonium salts contain NH₄⁺ instead of a metal ion.

Teacher's Note:
1. The cation here is ammonium.
2. Give two named salts.

Short Answer Questions

Question 17. Classify each of the following substances as a weak acid, strong acid, weak base, strong base:
(a) HClO₄ (b) CH₃COOH (c) NaOH (d) NH₄OH
Answer:
(a) HClO₄: strong acid.
(b) CH₃COOH: weak acid.
(c) NaOH: strong base.
(d) NH₄OH: weak base.
In simple words: Classify by how completely each substance ionises.

Teacher's Note:
1. NaOH and KOH are strong bases; NH₄OH is weak.
2. Perchloric acid is a strong acid.

Question 18. Write two observations you would make when quick lime is added to water.
Answer:
(i) The mixture becomes hot, because the reaction is highly exothermic.
(ii) A milky solution (slaked lime suspension) is formed: CaO + H₂O → Ca(OH)₂ + heat.
In simple words: Quick lime reacts with water and gives out heat.

Teacher's Note:
1. Name the product slaked lime.
2. Write the equation.

Question 19. What happens to most of the molecules of a strong acid when the acid is mixed with water?
Answer:
Most of the molecules of a strong acid ionise and give H⁺ ions. These H⁺ ions combine with water to form hydronium ions, H₃O⁺. So most of the molecules get converted to hydronium ions.
In simple words: A strong acid ionises almost completely in water.

Teacher's Note:
1. Weak acids ionise only slightly.
2. Write the equation for HCl.

Question 20. Write the chemical name and formula of washing soda. What happens when crystals of washing soda are exposed to air?
Answer:
Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O.
On exposure to air the crystals lose water of crystallisation and change to a white powder (sodium carbonate monohydrate): Na₂CO₃·10H₂O → Na₂CO₃·H₂O + 9H₂O. This is efflorescence.
In simple words: Washing soda crystals lose water in air and become a powder.

Teacher's Note:
1. Name the process: efflorescence.
2. Count 10 and 9 water molecules.

Question 21. Write the balanced equation in molecular form illustrating the complete neutralization of Al(OH)₃ with H₂SO₄.
Answer:
Each Al(OH)₃ needs three H⁺ and each H₂SO₄ gives two H⁺, so 2Al(OH)₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 6H₂O.
In simple words: Two Al(OH)₃ react with three H₂SO₄.

Teacher's Note:
1. Balance Al first, then SO₄, then H and O.
2. This is a neutralisation reaction.

Question 22. Name the acid present in the following:
(i) Tomato (ii) Vinegar (iii) Tamarind
Answer:
(i) Tomato: oxalic acid (also citric and malic acid).
(ii) Vinegar: acetic acid.
(iii) Tamarind: tartaric acid.
In simple words: Natural sources contain organic acids.

Teacher's Note:
1. Learn the NCERT table of natural acids.
2. Learn the natural sources of acids from the NCERT table.

Question 23. What is water of crystallisation? Give some examples of salts having water of crystallisation.
Answer:
Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.
Examples: copper sulphate pentahydrate, CuSO₄·5H₂O; washing soda, Na₂CO₃·10H₂O; gypsum, CaSO₄·2H₂O; ferrous sulphate, FeSO₄·7H₂O.
In simple words: Hydrated salts hold a definite number of water molecules in the crystal.

Teacher's Note:
1. Remember the numbers 5, 10, 2 and 7.
2. Name at least two examples.

Question 24. What is meant by strong acids and weak acids? Classify the following into strong acids and weak acids: CH₃COOH, H₂SO₄, HNO₃, H₂CO₃, H₂SO₃.
Answer:
A strong acid ionises almost completely in water and gives a large number of H⁺ ions. A weak acid ionises only slightly in water and gives few H⁺ ions.
Strong acids: H₂SO₄ and HNO₃. Weak acids: CH₃COOH, H₂CO₃ and H₂SO₃.
In simple words: Strong acids ionise fully, weak acids only partly.

Teacher's Note:
1. Learn the strong acids: HCl, H₂SO₄, HNO₃.
2. Give the classification in a list.