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