You are given the following metals:
Mg, Ca, Na, Zn, Al
Write their reaction with water and hence arrange them in
the decreasing order of their reactivity.
Ans. Mg, Ca, Na, Zn, Al.
(i) Sodium reacts with water to evolve hydrogen which
immediately catches fire producing a lot of heat.
2Na + 2H2O → 2NaOH + H2 + Heat energy.
(ii) Calcium reacts with water less vigorously, hence heat
evolved is not sufficient for hydrogen to catch fire. Calcium starts floating
because the bubbles of hydrogen sticks to it.
Ca + 2H2O → Mg(OH)2 + H2
(iii) Magnesium reacts with hot water to form magnesium
hydroxide and hydrogen. Magnesium also starts floating like calcium.
Mg + 2H2O → Mg(OH)2 + H2.
(iv) Metals like Aluminium and Zinc do not react with cold
or hot water but they react with steam to firm metal oxide and hydrogen gas.
3Fe + 4H2O → Fe3O4 + 4H2
(v) Order of reactivity : Na > Ca > Mg > Al > Zn
