CBSE Class 10 Science Acids Bases And Salts Worksheet Set 09

This second printable worksheet for Class 10 Science Chapter 2, Acids, Bases and Salts, contains 15 short questions with answers on soil treatment, the strength of acids, dilution of sulphuric acid, litmus tests, the action of acids on carbonates and metals, and the colour of copper sulphate. It prints neatly on one or two pages for revision.

Very Short and Short Answer Questions

Question 1. The soil in a field is highly acidic. List any two materials which can be added to this soil to reduce its acidity. Give the reason of your choice.
Answer:
Quick lime (calcium oxide), slaked lime (calcium hydroxide) or chalk (calcium carbonate) can be added.
They are basic, so they neutralise the acid in the soil and reduce its acidity.
In simple words: Add a base to acidic soil.

Teacher's Note:
1. Name any two materials.
2. Reason: neutralisation.

Question 2. The pH of soil A is 7.5 while that of soil B is 4.5. Which of the two soils A or B should be treated with powdered chalk to adjust its pH and why?
Answer:
Soil B (pH 4.5) should be treated with powdered chalk.
Soil B is acidic, which is not good for plant growth. Chalk (calcium carbonate) is basic and neutralises the acid, bringing the pH close to 7.
In simple words: Add chalk to acidic soil.

Teacher's Note:
1. Soil A is slightly basic.
2. Chalk neutralises the soil acid.

Question 3. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer:
The farmer treats the soil with quick lime, slaked lime or chalk when the soil is acidic (pH less than 7). These substances are basic and neutralise the excess acid, making the soil suitable for crops.
In simple words: Add lime to acidic soil.

Teacher's Note:
1. These three substances are bases.
2. Neutral soil is best for crops.

Question 4. Why does distilled water not conduct electricity, whereas rain water does?
Answer:
Distilled water contains no dissolved ionic substances, so it has no ions to carry the current.
Rain water dissolves acidic gases such as CO₂ and SO₂ from the air and forms acids like carbonic acid and sulphurous acid, which give ions, so it conducts electricity.
In simple words: Ions are needed for conduction.

Teacher's Note:
1. Rain water is slightly acidic.
2. Pure water is a very poor conductor.

Question 5. Yellow stain of an Indian style vegetable curry on a white cloth turns reddish brown on application of soap on the cloth. What is the reason behind this? What is the colour of litmus solution, when it is neither acidic nor basic?
Answer:
Curry contains turmeric, which is a natural indicator. Soap is basic, and turmeric turns reddish-brown in a basic medium.
Litmus solution is purple when it is neither acidic nor basic.
In simple words: Turmeric changes colour in a base.

Teacher's Note:
1. On rinsing, the stain becomes yellow again.
2. Litmus is purple in neutral solution.

Question 6. 20 mL of water and 15 mL of sulphuric acid are to be mixed in a beaker.
(a) State the method that should be followed with reason.
(b) What is this process known as?
Answer:
(a) The acid should be added slowly to the water with constant stirring. Mixing an acid with water is highly exothermic, and adding the acid to water lets the large amount of water absorb the heat evenly, avoiding splashing and breaking of the glass.
(b) The process is called dilution of the acid.
In simple words: Add acid to water slowly with stirring.

Teacher's Note:
1. Do not add water to the acid.
2. Use the word dilution.

Question 7. Out of the two, hydrochloric acid and acetic acid, which one is considered a strong acid and why? Write the name or molecular formula of one more strong acid.
Answer:
Hydrochloric acid is the strong acid, because it ionises completely and releases H⁺ ions in aqueous solution more easily than acetic acid.
This can be verified with universal indicator: it turns red with HCl (pH about 2) and yellow/orange with acetic acid (pH about 4).
Another strong acid: sulphuric acid, H₂SO₄ (or nitric acid, HNO₃).
In simple words: HCl ionises fully; acetic acid ionises partly.

Teacher's Note:
1. Compare the colours with universal indicator.
2. Name one more strong acid.

Question 8. A gas is liberated immediately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate powder in a test tube. Name the gas evolved and describe the test that confirms the identity of the gas.
Answer:
The gas liberated is carbon dioxide.
Test: pass the gas through lime water. It turns lime water milky, which confirms carbon dioxide.
In simple words: Carbon dioxide turns lime water milky.

Teacher's Note:
1. Equation: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂.
2. Mention brisk effervescence.

Teacher's Note:
1. Baking soda is a mild base, so its colour is light.
2. Acetic acid is a weak acid.

Question 10. A substance X is used as building material and insoluble in water. When it reacts with dil. HCl it produces a gas which turns lime water milky. Predict the substance and write the chemical equation involved.
Answer:
The substance X is calcium carbonate (limestone or marble), CaCO₃.
CaCO₃ + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
In simple words: Limestone gives CO₂ with acid.

Teacher's Note:
1. CO₂ turns lime water milky.
2. Marble is used in buildings.

Question 11. What happens when a few drops of water are added to anhydrous copper sulphate? Explain with the help of an equation.
Answer:
Anhydrous copper sulphate is white. On adding water it becomes hydrated and turns blue due to the formation of hydrated copper sulphate.
CuSO₄ (white) + 5H₂O → CuSO₄·5H₂O (blue)
In simple words: White copper sulphate turns blue with water.

Teacher's Note:
1. This is a test for water.
2. Write colours with the equation.

Question 12. Most metals do not react with bases, but zinc metal does. Suggest a reason. Write an equation for the reaction between Zn and NaOH.
Answer:
Zinc is amphoteric in nature, so it reacts with both acids and strong bases.
Zn + 2NaOH → Na₂ZnO₂ + H₂
In simple words: Zinc reacts with acids and with strong bases.

Teacher's Note:
1. Aluminium also reacts with NaOH.
2. Sodium zincate is the salt formed.

Question 13. Explain the reaction of dilute HCl on the following substance with the help of chemical equation:
(a) Magnesium ribbon (b) Sodium hydroxide (c) Crushed egg shells
Answer:
(a) Hydrogen gas is released: Mg + 2HCl → MgCl₂ + H₂↑.
(b) Neutralisation occurs and salt and water are formed: NaOH + HCl → NaCl + H₂O.
(c) Egg shell is calcium carbonate, so carbon dioxide is released with effervescence: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑.
In simple words: Dilute HCl gives H₂ with metals, salt and water with bases, and CO₂ with carbonates.

Teacher's Note:
1. Name the type of reaction in each part.
2. Balance each equation.

Question 14. How is the concentration of hydroxide ions (OH⁻) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer:
When excess base is dissolved in a solution of sodium hydroxide, more hydroxide ions are added to the solution.
So the concentration of OH⁻ ions increases, if the base dissolves and ionises. A saturated solution does not dissolve more base, and then the concentration stays the same.
In simple words: More dissolved base gives more OH⁻ ions.

Teacher's Note:
1. The word excess hints at the solution getting more basic.
2. pH increases as the OH⁻ concentration increases.

Question 15. Name the sodium compound which is used for softening hard water. What will happen if the solution of sodium hydrogen carbonate is heated? Write the chemical equation involved.
Answer:
Washing soda (sodium carbonate decahydrate), Na₂CO₃·10H₂O, is used for softening hard water.
When a solution of sodium hydrogencarbonate is heated, it decomposes to give sodium carbonate and carbon dioxide gas: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂↑.
In simple words: Washing soda softens water; heating baking soda gives sodium carbonate.

Teacher's Note:
1. Balance the equation.
2. Baking soda is NaHCO₃ and washing soda is Na₂CO₃·10H₂O.