CBSE Class 10 Science Acids Bases And Salts Worksheet Set 08

This printable Class 10 Science worksheet for Chapter 2, Acids, Bases and Salts, has 19 short questions with answers on natural indicators, natural acids, definitions, ionisation equations, the pH of everyday solutions and common facts about plaster of Paris. It is arranged to print on a page or two for quick revision before a test.

Very Short Answer Questions

Question 1. Name two flowers whose colour of petals can be used as indicator.
Answer:
Petunia and geranium (also hydrangea).
In simple words: Some flower petals act as natural indicators.

Teacher's Note:
1. Their colour changes with acid or base.
2. Red cabbage leaves also work.

Question 2. Name the planet that contains yellowish clouds of sulphuric acid.
Answer:
Venus.
In simple words: The atmosphere of Venus has clouds of sulphuric acid.

Teacher's Note:
1. Life as we know it cannot exist there.
2. Value: scientific curiosity.

Question 3. A bud of petunia became reddish purple after first shower of rain. What does it indicate?
Answer:
It indicates that the rain water is acidic, because petunia petals are natural indicators that turn reddish-purple in an acidic medium.
In simple words: Petunia petals change colour with acid.

Teacher's Note:
1. Acid rain has pH below 5.6.
2. Natural indicators come from flowers.

Question 4. A woman found that the cake made by her is hard and small in size. Which ingredient has she forgotten to add that would have cause the cake rise and become light?
Answer:
She forgot to add baking powder (a mixture of baking soda and tartaric acid). It releases carbon dioxide on heating, which makes the cake rise and become light.
In simple words: Baking powder makes cakes rise.

Teacher's Note:
1. The same applies to bread.
2. Mention carbon dioxide.

Teacher's Note:
1. Learn this table from NCERT.
2. Tamarind has tartaric acid.

Question 6. What is dilution? Write one word/term for the following:
(i) Water soluble base (ii) A substance which dissociates on dissolving in water to produce hydrogen ions (iii) A reaction between an acid and a base to form salt and water (iv) A substance which dissociates on dissolving in water to produce hydroxide ions
Answer:
Dilution: mixing an acid or base with water decreases the concentration of ions (H₃O⁺ or OH⁻) per unit volume; the acid or base is said to be diluted.
(i) Alkali. (ii) Acid. (iii) Neutralisation reaction. (iv) Base.
In simple words: Dilution lowers ion concentration; four key terms.

Teacher's Note:
1. One-word answers are enough for the second part.
2. Dilution does not change the nature.

Question 7. Two solutions A and B have pH values of 3.0 and 10.5 respectively. Which of these will turn phenolphthalein from colourless to pink? Which of these will turn blue litmus solution to red?
Answer:
Solution B (pH 10.5, basic) will turn phenolphthalein from colourless to pink.
Solution A (pH 3.0, acidic) will turn blue litmus red.
In simple words: Bases turn phenolphthalein pink; acids turn blue litmus red.

Teacher's Note:
1. pH below 7 is acidic.
2. pH above 7 is basic.

Question 8. Three solutions A, B and C have pH values of 6, 2 and 10 respectively. Which of the solutions is highly acidic? Which solution will turn red litmus blue?
Answer:
Solution B (pH 2) is highly acidic.
Solution C (pH 10) will turn red litmus blue, because it is basic.
In simple words: Lowest pH is most acidic; pH above 7 turns red litmus blue.

Teacher's Note:
1. A (pH 6) is weakly acidic.
2. Compare each pH with 7.

Question 9. P and Q are aqueous solutions of sodium chloride and sodium hydroxide respectively. Which of these will turn:
(i) Blue litmus to red or (ii) Red litmus to blue? Give justification for your answer.
Answer:
(i) Neither. Sodium chloride (P) is a neutral salt of a strong acid and a strong base, so it has no effect on blue or red litmus. Blue litmus turns red only in an acid.
(ii) Q (sodium hydroxide) turns red litmus to blue, because it is a basic solution that gives OH⁻ ions.
In simple words: Only a base turns red litmus blue; NaCl is neutral.

Teacher's Note:
1. Give the reason with each answer.
2. Learn the colour of each indicator in acid and in base.

Question 10. The pH scale can be used to determine the strength of acid solutions as well as basic solutions by making use of hydrogen ion concentrations in them. Consider two solutions A and B having pH values 3 and 9.5, respectively.
(i) Which solution will turn blue litmus red?
(ii) Which solution will turn phenolphthalein from colourless to pink?
(iii) Water is a neutral substance. What colour will you get when you add a few drops of universal indicator to a test tube containing distilled water?
Answer:
(i) Solution A (pH 3, acidic) turns blue litmus red.
(ii) Solution B (pH 9.5, basic) turns phenolphthalein pink.
(iii) Green, because the pH of distilled water is 7.
In simple words: Acids turn blue litmus red; bases turn phenolphthalein pink; water is green with universal indicator.

Teacher's Note:
1. Compare the pH with 7.
2. Universal indicator is green at pH 7.

Question 11. Name two industries based on use of washing soda.
Answer:
The glass industry and the soap and paper industries (also manufacture of caustic soda and borax). Washing soda is also used for removing permanent hardness of water.
In simple words: Washing soda is used in glass, soap and paper industries.

Teacher's Note:
1. Mention two industries.
2. Write the answer in short, clear steps.

Question 12. Write the chemical equation for reaction between plaster of paris and water.
Answer:
CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O. Plaster of Paris reacts with water to form gypsum, which sets as a hard mass.
In simple words: POP + water gives hard gypsum.

Teacher's Note:
1. Equation can be written as 2CaSO₄·½H₂O + 3H₂O → 2CaSO₄·2H₂O.
2. This is the setting reaction.

Question 13. What do you understand by the term pH of a solution? What is the pH of distilled water and common salt solution?
Answer:
The pH of a solution tells us the concentration of H⁺ ions in it (pH = −log[H⁺]); it measures how acidic or basic the solution is.
The pH of distilled water is 7, and the pH of common salt solution is also 7, because sodium chloride is a neutral salt.
In simple words: pH measures acidity; water and salt solution are neutral.

Teacher's Note:
1. pH 7 is neutral.
2. NaCl does not change the pH of water.

Short Answer Questions

Question 14. Why does an aqueous solution of an acid conduct electricity?
Answer:
An acid dissociates in water to form ions, for example HCl → H⁺ + Cl⁻.
These freely moving ions carry the electric current through the solution, so the solution conducts electricity.
On passing current, H⁺ ions move to the cathode and are discharged as hydrogen gas.
In simple words: Acid solutions contain ions, and moving ions carry current.

Teacher's Note:
1. Glucose and alcohol solutions do not conduct since they have no ions.
2. The conducting particles in a solution are ions, not electrons.

Question 15. How is the neutralisation of a carbonate with an acid different from the neutralisation of an oxide or a hydroxide?
Answer:
Reaction of a metal carbonate with an acid gives salt, water and carbon dioxide gas (brisk effervescence is seen): CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑.
Reaction of a metal oxide or hydroxide with an acid gives only salt and water, and no gas is evolved: CuO + 2HCl → CuCl₂ + H₂O.
In simple words: Carbonates also give CO₂ gas, oxides and hydroxides do not.

Teacher's Note:
1. Remember that CO₂ turns lime water milky.
2. Give one equation of each type.

Question 16. Write equations for (i) Dissociation of HCl in water.
(ii) Formation of hydronium ion.
(iii) NaOH is dissolved in water.
(iv) KOH is dissolved in water.
Answer:
(i) HCl + H₂O → H₃O⁺ + Cl⁻
(ii) H⁺ + H₂O → H₃O⁺
(iii) NaOH(s) → Na⁺(aq) + OH⁻(aq)
(iv) KOH(s) → K⁺(aq) + OH⁻(aq)
In simple words: Acids give H⁺ and bases give OH⁻ in water.

Teacher's Note:
1. Write the ions with their charges.
2. State symbols are optional.

Question 17. How will the following substances dissociate to produce ions in their solutions?
(i) Hydrochloric acid (ii) Nitric acid (iii) Sulphuric acid (iv) Sodium hydroxide (v) Potassium hydroxide (vi) Magnesium hydroxide
Answer:
(i) HCl(aq) → H⁺ + Cl⁻
(ii) HNO₃(aq) → H⁺ + NO₃⁻
(iii) H₂SO₄(aq) → 2H⁺ + SO₄²⁻
(iv) NaOH(aq) → Na⁺ + OH⁻
(v) KOH(aq) → K⁺ + OH⁻
(vi) Mg(OH)₂(aq) → Mg²⁺ + 2OH⁻
In simple words: Acids give H⁺ and bases give OH⁻ ions.

Teacher's Note:
1. Balance the charges.
2. Sulphuric acid gives two H⁺ ions.

Question 18. State the following: (i) pH value of sodium chloride?
(ii) When a solution is added to a cloth strip treated with onion extract, then the smell of onion cannot be detected. State whether the given solution contains an acid or a base.
(iii) One animal and one plant whose stings contain formic acid (or methanoic acid).
(iv) How is the concentration of hydronium ions affected when a solution of an acid is diluted?
(v) What is the common name of water soluble bases?
(vi) What is common in all the water soluble bases (or alkalis)?
(vii) Which is more acidic a solution of pH = 2 or a solution of pH = 6?
(viii) What is dead burnt plaster?
Answer:
(i) 7 (neutral).
(ii) The solution contains a base, because the smell of onion is lost in a basic medium.
(iii) Animal: ant (or honey bee); plant: nettle.
(iv) The concentration of H₃O⁺ ions decreases.
(v) Alkalis.
(vi) All of them give hydroxide ions, OH⁻, in water.
(vii) The solution of pH = 2 is more acidic.
(viii) Dead burnt plaster is anhydrous calcium sulphate, CaSO₄.
In simple words: A mixed set of quick facts on indicators, pH and plaster.

Teacher's Note:
1. Learn each fact as a one-line answer.
2. Lower pH means a stronger acid.

Question 19. Column I lists tartaric acid, lactic acid, formic acid and citric acid. Column II lists calcium hydroxide, sodium hydroxide, ammonia and magnesium hydroxide.
(i) What does column I represent?
(ii) What does column II represent?
(iii) Name one source of citric acid.
(iv) What is released by ant's sting?
Answer:
(i) Column I represents acids.
(ii) Column II represents bases.
(iii) Oranges (lemon) are a good source of citric acid.
(iv) Formic acid (methanoic acid) is released by an ant's sting.
In simple words: Natural acids: tartaric (tamarind), lactic (curd), formic (ant), citric (orange).

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