NCERT Activity 3.9 Class 10 Science Explanation

In this activity, we will learn how different metals react with oxygen when burnt in air and compare their reactivity with oxygen.

What happens when Metals are burnt in air?

⚠️Caution

    1.  Teachers’ supervision is required

    2. Must wear goggles

    3. Use tongs to hold metals

Aim

 To observe and compare the reactivity of metals with oxygen

Materials Required

    1. Samples of metals (Mg, Al, Zn, Fe & Cu)

    2. Bunsen burner or spirit lamp

    3. Tongs

    4. Watch glass

    5. Water

    6. Litmus

    7. Beaker

Procedure

 We follow the following steps:

    1. Hold a small piece of metal with tongs.

   2. Burn each in the flame and observe the colour of the flame.

   3. Note how easily each sample burns.

   4. Collect the ash or product formed on a watch glass.

   5. Let the metal surface cool down.

   6. Test the solubility of the product in water and check the pH.

   7. Arrange the metals in the decreasing order of reactivity with oxygen.

Observation 

 (i) Potassium, Sodium and magnesium burn easily.

         2Mg(s) + O₂ 2MgO(s)

         MgO(s) + H₂O(l) Mg(OH)₂ (aq) 

(ii) Copper and aluminium do not burn but on heating in air form black copper (II) oxide and white aluminium oxide (Al₂O₃) respectively.

2Cu +O₂  → heat 2CuO

                   Cupric oxide

4Al + 3O₂(g) →2AI₂O₃(s)

(iii) Copper and aluminium metal oxides are insoluble in water. But, alkali metal oxides (Na₂O, K₂O) dissolve in water to produce alkalis.

The order of reactivity with oxygen is:

      K > Na > Mg > AI > Cu

 

We observe that :

   (1)      Magnesium (Mg)

i.              Ease of burning – Burns very easily

ii.          Colour of flame – White

iii.       Appearance after burning- White powder of MgO

iv.        Product solubility – Slightly soluble

v.           Nature of oxide – Basic or alkaline

(2)      Aluminium (Al)

   i.              Ease of burning – Burns with difficulty

   ii.          Colour of flame – White sparks

  iii.       Appearance after burning- White powder of Al₂O₃

  iv.        Product solubility – Insoluble

  v.  Nature of oxide – Amphoteric (both acidic and basic)

 

(3)      Zinc (Zn)

    i. Ease of burning –  Requires strong heating

   ii. Colour of flame –  Blue-green

   iii. Appearance after burning- Yellow

   iv. Product solubility – Insoluble

   v.  Nature of oxide – Amphoteric

 

(4)      Iron (Fe)

   i. Ease of burning – Does not burn easily

   ii. Colour of flame – Golden sparks

   iii. Appearance after burning-  Black

   iv. Product solubility – Insoluble

   v. Nature of oxide –Basic

(5)      Copper (Cu)

   i. Ease of burning – Difficult in burning

   ii. Colour of flame – Green

  iii. Appearance after burning- Black coating of copper oxide

   iv. Product solubility – Insoluble

vi.   Nature of oxide –Basic

Explanation

 Metals form metal oxides when burned in the air, and they are mostly basic in nature.

Conclusion

We can conclude that:

    1. Metals form metal oxides when they are burned in the air

     2. Metal oxides are basic in nature, but aluminium oxide is amphoteric.

   Frequently Asked Questions

    1. Which metal forms an amphoteric oxide when it burns?

Ans – Aluminium and Zinc

    2. What do you mean by amphoteric oxide?

Ans – These oxides react with both acids and bases and form salt and water.

    3. Are metal oxides soluble in water?

Answer – Most metal oxides are insoluble in water, but oxides of alkali and alkaline earth metals are soluble in water.

    4. Name some soluble metal oxides in water.

Answer- Na₂O , CaO, K₂O etc

Metals and Non-Metals Activities Solutions

S. No.	Topics
1	Activity 3.1
2	Activity 3.2
3	Activity 3.3
4	Activity 3.4
5	Activity 3.5
6	Activity 3.6
7	Activity 3.7
8	Activity 3.8
9	Activity 3.9
10	Activity 3.10
11	Activity 3.11
12	Activity 3.12
13	Activity 3.13
14	Activity 3.14