CBSE Class 10 Science Practical Skills – Properties of Acids and Bases

CBSE Class 10 Science Practical Skills – Properties of Acids and Bases

Basic Building Concepts

• Acids are sour in taste while bases are bitter in taste.
• When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed.
• When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of metal and oxygen.
• When an acid reacts with a metal carbonate, it gives the corresponding salt, carbon dioxide gas and water.
• Bases do not react with metal carbonate.

Aim
(a) To study the properties of acids (HCl) by their reaction with

1. Litmus solution(Blue/Red)
2. Zinc metal(Zn)
3. Solid sodium carbonate(Na₂CO_s).

Materials Required
Test tubes, test tube stand, test tube holder, cork, droppers, beaker, litmus (red and blue), Zn metal granules, solid sodium carbonate, dil. HCl.

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Theory

1. HCl is an acid. Acids turn blue litmus red and do not affect red litmus.
2. On reacting with zinc metal, it forms a salt, zinc chloride (ZnCl₂) and hydrogen gas (H₂) is liberated.
   Zn(s) + 2HCl(aq) → ZnCl₂(aq) +H₂↑
   Hydrogen gas burns in air with a pop sound.
   2H₂(g) + O₂(g) → 2H₂0(l)
3. HCl reacts with sodium carbonate (aqueous/solid) to liberate carbon dioxide(CO₂) which turns lime water milky. When excess of CO₂ is passed through the solution, the milkiness disappears.
   

Procedure And Observation Table

Result

1. HCI turns blue litmus red.
2. It releases H₂ gas on reaction with Zn metal.
3. It liberates C0₂ gas on reaction with Na₂C0₃.

Precautions

1. HCI is corrosive, therefore, handle it with care.
2. Use small quantities of chemicals.
3. A fine jet should be taken for burning hydrogen.
4. Use clean zinc metal, otherwise the reaction will occur very slowly.
5. Wash your hands properly with soap after the experiment.

Aim

(b) To study the properties of bases(NaOH) by their reaction with

1. Litmus solution(Blue/Red)
2. Zinc metal(Zn)
3. Solid sodium carbonate(Na₂CO₃)

Materials Required
Dil. NaOH, test tubes, test tube holder, test tube stand, red and blue litmus solutions, zinc metal, sodium carbonate and droppers.
Theory

1. NaOH is a base. Bases turn red litmus blue and do not affect blue litmus.
2. On reacting with zinc metal, NaOH forms sodium zincate and hydrogen gas is liberated. The hydrogen gas burns with a pop sound.
   
3. NaOH does not react with solid or aqueous Na₂CO₃.

Procedure And Observation Table

Result

1. NaOH turns red litmus blue.
2. On reaction with Zn metal, it releases H₂
3. It does not react with Na₂CO_g.

Precautions

1. Handle NaOH with care.
2. Use small quantities of chemicals.
3. A fine jet should be taken for burning hydrogen.
4. Zn granules should be clean.
5. Wash your hands properly after completing experiment.

INTERACTIVE SESSION

Question 1:
What is the aim of your experiment?
Answer:
The aim of my experiment is to study the properties of acids and bases.

Question 2:
What are acids?
Answer:
Acids are the substances which furnish hydrogen ions in a solution

Question 3:
What are bases?
Answer:
Bases are the substances which furnish hydroxide ions in a solution.

Question 4:
How does an acid affect blue and red litmus?
Answer:
An acid turns blue litmus red and has no effect on red litmus.

Question 5:
How does a base affect blue and red litmus?
Answer:
It turns red litmus blue and no change is observed on blue litmus.

Question 6:
Why do metals displace hydrogen from dilute acids?
Answer:
Metals displace hydrogen from dilute acids because they are more reactive than hydrogen. Metals lose electrons which the hydrogen ions from acids accept and hydrogen gas is liberated.

Question 7:
Do all metals displace hydrogen gas from dilute acids?
Answer:
No, only the metals which are above hydrogen in the reactivity series are able to displace hydrogen from dilute acids.

Question 8:
What would be the affect of milk of magnesia on litmus?
Answer:
It would turn red litmus blue as it is an antacid and basic in nature.

Question 9:
What would happen when dil. HCl and dil. NaOH (same concentrations) are mixed in equal amounts? Write the equation also.
Answer:
Neutralisation reaction occurs. As a result of this salt and water will be formed.
NaOH + HCl → NaCl + H₂0

Question 10:
Write the reaction occurring between HCl and Na₂CO₃.
Answer:
2HCl + Na₂CO₃ -> 2NaCl + H₂O + CO₂

Question 11:
How do you test CO₂ gas?
Answer:
When CO₂ is passed through lime water, it turns lime water milky.

Question 12:
Why does hydrogen gas burn with an explosion?
Answer:
Hydrogen gas has the highest calorific value with low ignition temperature and, therefore, burns with an explosion.

Question 13:
Write the reaction which occurs between Zn metal and dil. H₂SO₄.
Answer:
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

Question 14:
What is the difference between a strong and a weak acid?
Answer:
Strong acids are those which completely dissociate into ions.
For example,                HCl(aq) → H⁺(aq) + Cl^– (aq),
whereas weak acids are those which partially dissociate into ions.
For example,                CH₃COOH(aq)\(\rightleftharpoons\) CH₃COO^–(aq) + H⁺(aq)

Question 15:
Which out of hydrochloric acid and acetic acid would have a lower pH?
Answer:
HCl would have a lower pH as it has a higher concentration of hydrogen ions.

Question 16:
Which out of dil. H₂SO₄ and lime water would turn red litmus blue?
Answer:
Lime water being basic in nature will turn red litmus blue.

NCERT LAB MANUAL QUESTIONS

Question 1:
What will be the colour of a blue litmus paper on bringing it in contact with a drop of dil. hydrochloric acid?
Answer:
The colour of blue litmus turns red on bringing it in contact with a drop of dil. hydrochloric acid.

Question 2:
What will happen to a lighted candle if it is brought near the mouth of a gas jar containing hydrogen gas?
Answer:
The candle extinguishes with a pop sound and the gas burns with a pale blue flame.

Question 3:
Which gas is produced when zinc metal reacts with hydrochloric acid?
Answer:
Hydrogen gas is produced when zinc metal reacts with hydrochloric acid.
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Question 4:
Which gas is liberated when sodium carbonate reacts with hydrochloric acid?
Answer:
When sodium carbonate reacts with hydrochloric acid, CO₂ gas is liberated.
Na₂C0₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂0(l) + CO₂(g)

Question 5:
What will be the colour of a blue litmus paper on bringing it in contact with a drop of dil. NaOH?
Answer:
Blue litmus paper does not undergo any change in colour on bringing it in contact with a drop of dil. NaOH as dil. NaOH is a base and changes colour of red litmus to blue and has no effect on blue litmus.

PRACTICAL BASED QUESTIONS

Multiple Choice Questions/VSA

1. 10 ml of HCl and 10 ml of NaOH solutions are contained in two separate beakers labelled I and II respectively. On adding zinc granules to both, it is observed that at room temperature [CBSE 2012, AI 2009]
(a) gas is evolved vigorously in both.
(b) gas is evolved vigorously in beaker I but not so in beaker II.
(c) gas is evolved in beaker II but not in beaker I.
(d) no gas is evolved in either of the two beakers.

2. A student took two test tubes containing 2 ml of dilute hydrochloric acid and added zinc granules to test tube (A) and solid sodium carbonate to test tube (B) as shown below: [CBSE 2012, Foreign 2009]

The correct observation would be
(a) rapid reaction in both the test tubes
(b) slow reaction in (A) and rapid reaction in (B)
(c) rapid reaction in (A) but a slow reaction in (B)
(d) no reaction in any of the test tubes

3. A blue litmus paper was first dipped in dil. HCl and then in dil. NaOH solution. It was observed that the colour of the litmus paper [CBSE 2011]
(a) changed to’red
(b) changed first to red and then to blue
(c) changed blue to colourless
(d) remained blue in both the solutions

4. When a student added zinc granules to dilute HCl, a colourless and odourless gas was evolved, which was tested with a burning matchstick, it was observed that
(a) the matchstick continued to burn brilliantly
(b) the matchstick burnt slowly with a blue flame
(c) the matchstick extinguished and the gas burnt with pop sound
(d) the matchstick burnt with an orange flame

5. The milkiness in lime water is obtained due to the formation of
(a) Ca(HSO₃)₂
(b) Ca(HCO₃)₂
(c) CaO
(d) CaCO₃

6. When excess carbon dioxide is passed through lime water, its milkiness disappears due to the formation of
(a) Ca(HCO₃)₂
(b) CaCO₃
(c) NaHCO₃
(d) Na₂CO₃

7. Zn metal shows amphoteric behaviour. It can be shown by
(а) its reaction with dil. NaOH only
(b) its reaction with dil. HCl only
(c) its reaction with both dil. HCl and dil. NaOH
(d) it does not react with either dil. HCl or dil. NaOH

8. Which one of the following will be required to identify the gas evolved when dilute hydrochloric acid reacts with zinc metal? [Delhi 2007]
(а) Blue litmus solution
(b) Red litmus solution
(c) A burning splinter
(d) Lime water

9. Four students performed the reactions of a dil. hydrochloric acid and a solution of sodium hydroxide with zinc metal and solid sodium carbonate separately. They reported the possible reaction by ( ✓) and no reaction by (). [CBSE 2011]

In which of the following sets all observations are correct?
(a) A
(b) B
(c) C
(d) D

10. A teacher gave two test tubes, one containing water and the other containing sodium hydroxide solution, to the students and asked them to identify the test tube containing sodium hydroxide solution. Which one of the following can be used for correctly identifying the test tube containing sodium hydroxide solution? [CBSE 2011, AI 2007]
(a) Blue litmus
(b) Red litmus
(c) Sodium carbonate solution
(d) Dilute hydrochloric acid

11. A student added dil. HC1 to a test tube conta­ining zinc granules and made the following observations:
I. The zinc surface becomes dull and black.
II. A gas evolves which bums with a pop sound.
III. The solution is colourless.
The correct observations are
(a) I and II
(b) I and III
(c) II and III
(d) I, II and III

12. Which one of the following set-ups is the most appropriate for the evolution of hydrogen gas and its identification? [Delhi 2008]

(a) I
(b) II
(c) III
(d) IV

13. A solution in test tube ‘A’ turns red litmus blue, evolves hydrogen on reaction with Zn and does not react with sodium carbonate, whereas solution in test tube ‘B’ turns blue litmus red, liberates hydrogen on reaction with Zn and evolves CO₂ with Na₂CO₃. Identify ‘A’ and ‘B’.
(a) ‘A’ is an acid, ‘B’ is a base
(b) ‘A’ is a base, ‘B’ is an acid
(c) Both ‘A’ and ‘B’ are bases
(d) Both ‘A’ and ‘B’ are acids

14. Given below are certain chemical properties of substances.
I. It turns blue litmus red II.
II. It turns red litmus blue
III. It reacts with zinc and a gas evolves
IV. It reacts with solid sodium carbonate to give brisk effervescence
Which out of these properties are shown by dilute hydrochloric acid?
I and II only
I and III only
I, III and IV only
II, III and IV only

Short Answer Questions
1. What are acids? Give any two characteristics of acids.

2. Give any two points of difference between an acid and a base.

3. What are bases? How does a base like sodium hydroxide react with zinc?

4. What is litmus solution? What is its colour in (i) neutral (ii) acidic and (iii) basic solutions?

5. What will happen:
(a) if a lighted candle is brought near the mouth of gas jar containing hydrogen gas?
(b) if carbon dioxide gas is passed through lime water?

ANSWER KEY

Multiple Choice Questions/VSA
1. (b)
2. (a)
3. (b)
4. (c)
5. (d)
6. (a)
7. (c)
8. (c)
9. (d)
10. (b)
11. (d)
12. (b)
13. (b)
14. (c)

Short Answer Questions
1. Acids are substances which contain hydrogen and which when dissolved in water give hydrogen ions in the solution.
Characteristics of acids:

1. They are sour in taste.
2. They turn blue litmus red but they do not affect red litmus.

2.

3. A base is a substance which when dissolved in water gives hydroxide (OH^–) ions in the solution. Sodium hydroxide reacts with zinc to liberate hydrogen gas along with the formation of sodium zincate.

4. Litmus solution is a purple coloured dye which is extracted from lichen. It is the most commonly used indicator in the laboratory.
Neutral litmus solution has purple colour. In acidic solution, it turns red whereas in basic solution, it turns blue.

5. (a) The candle extinguishes with a pop sound and the gas burns with a pale blue flame.
(b) CO₂ turns lime water milky.

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