Thursday, April 29, 2021

Acids, Bases and Salts | Class 10 | Activity 2.15 with Solution

Activity 2.15  
  • Heat a few crystals of copper sulphate in a dry boiling tube.
  • What is the colour of the copper sulphate after heating?
✅ Answer: White. 
  • Do you notice water droplets in the boiling tube? Where have these come from?
✅ Answer: Copper sulphate crystals contain water of crystallisation. When heated the crystals, this water is removed and the salt turns white.
  • Add 2-3 drops of water to the sample of copper sulphate obtained after heating.
  • What do you observe? Is the blue colour of copper sulphate restored?
✅ Answer: Copper sulphate crystals restore its blue colour. 

Acids, Bases and Salts | Class 10 | Activity 2.14 with Solution

Activity 2.14
  • Collect the following salt samples – sodium chloride, potassium nitrate, aluminium chloride, zinc sulphate, copper sulphate, sodium acetate, sodium carbonate and sodium hydrogen carbonate (some other salts available can also be taken).
  • Check their solubility in water (use distilled water only).
  • Check the action of these solutions on litmus and find the pH using a pH paper.
  • Which of the salts are acidic, basic or neutral?
  • Identify the acid or base used to form the salt.
  • Report your observations in Table 2.4.

Salt

pH

Acid used

Base used

 

 

 

 


✅ Answer:

Salt

pH

Acid used

Base used

Sodium chloride

7

HCl

NaOH

Potassium nitrate

7

HNO3

KOH

Aluminium chloride

7

HCl

Al(OH)3

Zinc sulphate

7

H2SO4

Zn(OH)2

Copper sulphate

< 7

H2SO4

Cu(OH)2

Sodium acetate

> 7

CH3COOH

NaOH

Sodium carbonate

> 7

H2CO3

NaOH

Sodium hydrogen carbonate

> 7

H2CO3

NaOH



Acids, Bases and Salts | Class 10 | Activity 2.13 with Solution

Activity 2.13  
  • Write the chemical formulae of the salts given below.
Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.
  • Identify the acids and bases from which the above salts may be obtained.
✅ Answer:

Salts & their Chemical formulae

Formed from which Acids & bases?

Potassium sulphate (K2SO4)

H2SO& KOH

Sodium sulphate (Na2SO4)

H2SO& NaOH

Calcium sulphate (CaSO4)

H2SO4 & CaCO3

Magnesium sulphate (MgSO4)

H2SO4 & Mg(OH)2

Copper sulphate (CuSO4)

H2SO4 & Cu(OH)2

Sodium chloride (NaCl)

HCl & NaOH

Sodium nitrate (NaNO3)

HNO3 & NaOH

Sodium carbonate (Na2CO3)

H2CO3 & NaOH

Ammonium chloride (NH4Cl)

HCl + NH4OH

  • Salts having the same positive or negative radicals are said to belong to a family. For example, NaCl and Na2SO4 belong to the family of sodium salts. Similarly, NaCl and KCl belong to the family of chloride salts. How many families can you identify among the salts given in this Activity?
✅ Answer: Na2SO4NaCl, NaNO3 and Na2CObelong to the family of sodium salts. K2SO4, Na2SO4, CaSO4, MgSO4, CuSO4 belong to the family of sulphate salts. NaCl and KCl belong to the family of chloride salts.

Acids, Bases and Salts | Class 10 | Activity 2.12 with Solution

Activity 2.12  
  • Put about 2 g soil in a test tube and add 5 mL water to it.
  • Shake the contents of the test tube.
  • Filter the contents and collect the filtrate in a test tube.
  • Check the pH of this filtrate with the help of universal indicator paper.
  • What can you conclude about the ideal soil pH for the growth of plants in your region?
✅ Answer: Ideal soil pH for the growth of plants = 6 to 7.

Acids, Bases and Salts | Class 10 | Activity 2.11 with Solution

Activity 2.11
  • Test the pH values of solutions given in Table 2.2.
  • Record your observations.
  • What is the nature of each substance on the basis of your observations?

Solution

Colour of pH paper

Approximate pH value

Nature of substance

1.    Saliva (before meal)




2.    Saliva (after meal)




3.    Lemon juice




4.    Colourless aerated drink




5.    Carrot juice




6.    Coffee




7.    Tomato juice




8.    Tap water




9.    1M NaOH




10. 1M HCl





✅ Answer:

Solution

Colour of pH paper

Approximate pH value

Nature of substance

1.    Saliva (before meal)

Green

6.8 – 7.4

Slightly acidic to basic

2.    Saliva (after meal)

Yellow green

5.8

Acidic

3.    Lemon juice

Orange

2.2

Acidic

4.    Colourless aerated drink

Yellow

4.0

Acidic

5.    Carrot juice

Yellow green

6.0

Acidic

6.    Coffee

Yellow

4.5

Acidic

7.    Tomato juice

Yellow

4.3

Acidic

8.    Tap water

Green

6 – 8.5

Varied

9.    1M NaOH

Dark blue

14

Basic

10. 1M HCl

Red

0

Acidic