Tag: chemistry

Reaction of 'Na' with cold water. 

Hardness of water due to bicarbonate ion is temporary and can be removed by boiling or through precipitation with calcium hydroxide.

By adding Na$ _{2} $Co$ _{3} $, all the Ca$ ^{+2} $ and and Mg$ ^{+2} $ ions which causes permanent hardness are replaced by Na$ ^{+} $, which doesn't cause hardness.

Permanent hardness of water is due to sulphate ion and chloride ion and cannot be easily removed. It can be removed by treating with washing soda.

Spring water, well water, and river water all are natural water.

Sodium with cold water produces $\displaystyle NaOH, : H _2$
$\displaystyle 2Na + 2H _2O \rightarrow 2Na^+  + 2 OH^- + H _2 \uparrow $

Sodium hydroxide in water gives colorless solution.
Sodium hydroxide is colourless. In water, it dissociates into sodium ions and chloride ions. These ions are also colourless.
$\displaystyle NaOH (aq)   \xrightarrow{H _2O} Na^+ (aq) + OH^- (aq)$

Alkali earth metals (Ca, Sr, Ba) react, vigorously with cold water.
Be does not react even with boiling water. Mg reacts with boiling water.

Potassium's reaction with water produces hydrogen gas of bluish pink.
Potassium reacts with cold water and gives potassium hydroxide and hydrogen gas.
$\displaystyle 2K + 2H _2O \rightarrow 2KOH + H _2$
The reaction is exothermic and the resulting solution is basic.
The reaction is so vigorous that the evolved hydrogen catches fire spontaneously.

Sea water contains around 400 ppm calcium. In lithosphere, the occurrence of Ca is 4.6% by weight. Of the alkaline earth metals, calcium rank fifth in abundance in the earth crust.