Activity 1.5 Class 10 Science

Aim of the activity 

The aim is to observe the changes that occur when Ferrous sulphate crystals are heated and to study the chemical reaction 

Material used in the activity

1. Ferrous sulphate crystals 

2. Dry boiling tube

3. Spirit lamp 

4. Test tube holder

5. Goggles

Procedure 

We will put about 2 grams of Ferrous sulphate crystals in a dry boiling tube, hold the boiling tube with a test tube holder and heat it gently over the flame of the spirit lamp.

Observation 

Before Heating

The ferrous sulphate crystals are pale green.

During Heating 

Ferrous sulphate crystals have water of crystallization that evaporates during heating so the crystals turn white.

After Heating

After continuous heating, the final residue is brown Ferric oxide (`Fe_2O_3`), and a pungent smell indicates the evolution of gases.

These gases are sulphur dioxide (`SO_2`) and sulphur trioxide (`SO_3`)

Explanation 

Step 1: Loss of water of crystallisation 

When ferrous sulphate is heated, the water of crystallization evaporates.

`FeSO_4.7H_2O heat →FeSO_4 + 7H_2O`

Due to water loss of crystallization, the pale green crystals turn white.

Step 2: Thermal Decomposition 

Now on continuous heating, dry ferrous sulphate (FeSO4) crystals decompose into ferric oxide sulphur dioxide and sulphur trioxide.

`2FeSO_4 →Fe_2O_3 + SO_2 + SO_3`

A pungent smell is observed due to these gases.

Conclusion 

In this activity, ferrous sulphate crystals lose their water crystallization and on further heating decompose into ferric oxide sulphur dioxide and sulphur trioxide gases.

This decomposition reaction.

Frequently Asked Question 

1. What type of chemical reaction takes place in this activity?

Ans – Thermal Decomposition reaction 

2. What is the colour of ferrous sulphate crystals?

Ans- Pale green

3. What is the colour of ferrous sulphate crystals when they are heated?

Ans - White

4. What is the final residue of this chemical reaction?

Ans – Ferric oxide in the solid form and `SO_2` and `SO_3` are gases.

5. What is the smell of the gases that evolved during the reaction?

Ans – The gases have a pungent smell that is suffocating.

6. What is the colour of ferric oxide?

Ans – Brwon

7. What is thermal decomposition?

Ans - The chemical reactions in which a single substance breaks down when they are heated. So energy in the form of heat is required.

Important extra points

1. The chemical formula of ferrous sulphate crystals is `FeSO_4.7H_2O`

2. The reaction in the activity is thermal decomposition and dehydration of hydrated ferrous sulphate crystals.

3. This reaction is used in the production of Ferric oxide.

4. Sulphur dioxide is a pollutant and causes acid rain.

5. Ferric oxide is used in the manufacturing of pigments.

Safety Precautions

1. Always wear safety goggles and gloves.

2. Ensure proper ventilation.

3. Keep your nose away from the gases as these gases are toxic and suffocating.

You can also explore

1. Identification tests for gases that evolved during this activity.

2. Heat other crystals like `CuSO_4.5H_2O`, `Na_2CO_3.10H_2O` etc.

3. Explore physical and chemical changes and note them down in your notebook.

Multiple Choice Questions

1. What is the colour of Ferrous sulphate crystals before heating?

a.White 

b.Pale green

c.Brown

d.Black

Correct answer – (b)Pale green

2. What type of chemical reaction takes place when ferrous sulphate is heated?

a.Combination reaction

b.Decomposition reaction 

c.Displacement reaction 

d.Neutralization reaction 

Correct answer – (b) Decomposition reaction 

3. What is the final colour of the residue left in this activity?

a.Black

b.Brown

c.Green 

d.Yellow

Correct answer-  (b)  Brwon

4. What gases are evolved during the heating of ferrous sulphate crystals?

a.`CO_2 and H_2`

b.`O_2 and N_2`

c.`SO_2 and SO_3`

d.`Cl_2 and H_2`

Correct answer- (c) `SO_2 and SO_3`

5. What is the chemical formula of ferrous sulphate crystals?

a.`FeSO_4`

b.`FeSO_4.7H_2O`

c.`FeSO_4.5H_2O`

d.`FeO`

Correct answer- (b) `FeSO_4.7H_2O`

6. Why do ferrous sulphate crystals lose their green colour on heating?

a.Due to loss of hydrogen

b.Due to loss of water of crystallization

c.Due to decomposition of ferrous sulphate 

d.Due to loss of water of crystallization

Correct answer –(b)Due to loss of water of crystallization

7. What is the residue formed after the decomposition of ferrous sulphate?

a.Ferric oxide 

b.Ferric sulphate

c.Ferrous chloride

d.Iron metal

Correct answer – (a) Ferric oxide

8. What is the smell of the gases that evolved during this activity?

a.Odorless 

b.Sweet 

c.Pungent 

d.Fruity 

Correct answer – (c) Pungent

9. What happens to the water of crystallization?

a.Gets decomposed 

b.Gets evaporate

c.Remains in compound 

d.None of them

Correct answer –(b)

10. What type of salt is ferrous sulphate before heating?

a.Anhydrous salt

b.Hydrated salt

c.Basic salt

d.Acidic salt

Correct answer –(b) Hydrated salt

11. What is the main use of ferric oxide?

a.Cleaning agent

b.Pigment in paints

c.Fertilizer

d.Antiseptic

Correct answer-(b) Pigment in paints

12. Which is the correct equation for the thermal decomposition of ferrous sulphate?

                                      heat

a. `2FeSO_4→  Fe_2O_3 + SO_2 + SO_3`

                                    heat

b. `FeSO_4 → Fe + SO_2 + O_2`

                                  heat

c. `FeSO_4→FeSO_4 + 7H_2O`

                                                      heat

d.`FeSO _4 + H_2→ Fe + H_2SO_`4

 

                                                                                                 heat

Correct Answer:  (a). `2FeSO_4→  Fe_2O_3 + SO_2 + SO_3`

13. What is the effect on the environment of sulphur dioxide and sulphur trioxide gases?

a.Acid rain

b.Global warming

c.Ozone depletion 

d.Deforestation 

Correct answer –(a) Acid rain

14. What is the nature of sulphur dioxide gas?

a.Acidic 

b.Basic 

c.Neutral 

d.Amphoteric

Correct answer –(a) Acidic

Related Topics

1. Activity 1.5 Video