Page 88 - Chemistry ICSE Class IX

76 ICSE Chemistry – 9
5. Reaction with metals. Different metals react with water under
different conditions.
ƒ With cold water: Certain metals like sodium and potassium attack
cold water very vigorously, whereas metals like barium, calcium
and lithium react with cold water slowly. In each case, hydrogen is
liberated and the hydroxide of the metal is formed.
vigorously
2Na + 2H O o 2NaOH(aq) + H (g)
2
2
sodium cold sodium hydroxide hydrogen
vigorously
2K + 2H O o 2KOH(aq) + H (g)
2
2
potassium cold potassium hydroxide hydrogen
slowly
Ca + 2H O o Ca(OH) (aq) + H (g)
2
2
2
calcium cold calcium hydroxide hydrogen
ƒ With boiling water: Magnesium, aluminium and zinc do not react
with cold water. These metals decompose boiling water to give the
corresponding metal oxide and hydrogen.
Mg(s) + H O(l) o MgO(s) + H (g)
2
2
magnesium boiling magnesium oxide hydrogen
Zn(s) + H O(l) o ZnO(s) + H (g)
2
2
zinc boiling zinc oxide hydrogen
ƒ With steam: Iron, cobalt, nickel, tin and lead are less reactive. These
metals react with water only when superheated steam (at high
temperature) is passed over heated metal.
DĞƚĂůƐ ůŝŬĞ ĐŽƉƉĞƌ͕ ƐŝůǀĞƌ ĂŶĚ ŐŽůĚ Š Iron reacts with steam reversibly to form ferrosoferric oxide and
ĂƌĞ ǀĞƌLJ ůĞƐƐ ƌĞĂĐƟǀĞ͘ dŚĞƐĞ ŵĞƚĂůƐ hydrogen.
ĂƌĞ ƵŶĂďůĞ ƚŽ ĚŝƐƉůĂĐĞ ŚLJĚƌŽŐĞŶ
ĨƌŽŵ ǁĂƚĞƌ͘ dŚĞƌĞĨŽƌĞ͕ ƚŚĞƐĞ ŵĞƚĂůƐ 3Fe(s) + 4H O U Fe O (s) + 4H (g)
3
4
2
2
ĚŽ ŶŽƚ ƌĞĂĐƚ ǁŝƚŚ ǁĂƚĞƌ ĞǀĞŶ ƵŶĚĞƌ iron steam ferrosoferric oxide hydrogen
ĚƌĂƐƟĐ ĐŽŶĚŝƟŽŶƐ͘ (red hot) (superheated)
Š Aluminium reacts with steam at temperatures above 800°C
forming its oxide and liberating hydrogen gas.
above 800° C
2Al(s) + 3H O(l) o Al O (s) + 3H (g)
2
2
2
3
aluminium steam aluminium oxide hydrogen
Activity Series of Metals from the Action of Water on
Some Metals
Different metals react with water under different conditions. Some metals
react with cold water, whereas some other metals react only with hot water
or steam at red hot. Some metals do not react with steam even at red hot.
Reactions of some common metals with water are described in
Table 3.1.

Table 3.1 Reaction of some common metals with water
Metal Reaction conditions Reaction
Sodium (Na) Reacts vigorously with cold water to give 2Na(s) + 2H O o 2NaOH(aq) + H (g)
2
2
hydrogen gas. cold
Magnesium (Mg) Does not react with cold water. With Mg(s) + H O o MgO(s) + H (g)
2
2
boiling water it gives hydrogen gas. boiling
Aluminium (Al) Aluminium decomposes boiling water 2Al(s) + 6H O o 2Al(OH) + 3H (g)
2
2
3
slowly to give hydrogen gas. boiling
Zinc (Zn) Zinc decomposes boiling water slowly and Zn(s) + H O o ZnO(s) + H (g)
2
2
steam rapidly. steam