Page 46 - NCERT Science Class 10 English Medium

3.2.1 What happens when Metals are burnt in Air?

You have seen in Activity 3.8 that magnesium burns in air with a dazzling
white flame. Do all metals react in the same manner? Let us check by
performing the following Activity.

Activity
Activity 3.9
Activity 3.93.9
Activity
Activity 3.9
3.9
CAUTION: The following activity needs the teacher’s assistance.
It would be better if students wear eye protection.
n Hold any of the samples taken above with a pair of tongs and try
burning over a flame. Repeat with the other metal samples.
n Collect the product if formed.
n Let the products and the metal surface cool down.
n Which metals burn easily?
n What flame colour did you observe when the metal burnt?
n How does the metal surface appear after burning?
n Arrange the metals in the decreasing order of their reactivity
towards oxygen.
n Are the products soluble in water?

Almost all metals combine with oxygen to form metal oxides.
Metal + Oxygen → Metal oxide
For example, when copper is heated in air, it combines with oxygen
to form copper(II) oxide, a black oxide.
2Cu + O → 2CuO
2
(Copper) (Copper(II) oxide)
Similarly, aluminium forms aluminium oxide.
4Al + 3O → 2Al O
2 2 3
(Aluminium) (Aluminium oxide)
Recall from Chapter 2, how copper oxide reacts with hydrochloric acid.
We have learnt that metal oxides are basic in nature. But some metal
oxides, such as aluminium oxide, zinc oxide show both acidic as well as
basic behaviour. Such metal oxides which react with both acids as well as
bases to produce salts and water are known as amphoteric oxides.
Aluminium oxide reacts in the following manner with acids and bases –
Al O + 6HCl → 2AlCl + 3H O
2 3 3 2
Al O + 2NaOH → 2NaAlO + H O
2 3 2 2
(Sodium
aluminate)
Most metal oxides are insoluble in water but some of these dissolve
in water to form alkalis. Sodium oxide and potassium oxide dissolve in
water to produce alkalis as follows –
Na O(s) + H O(l) → 2NaOH(aq)
2 2
K O(s) + H O(l) → 2KOH(aq)
2 2

Metals and Non-metals 41

2024-25