Question

Question #417b3

Answer 1

Warning! Long Answer!

Explanation:

To start, we need to understand what hardness is.

Scientifically, When water has any of the cations like `Ca^(2+), Mg^(2+), Fe^(2+), Al^(3+)` and any of the anions like `SO_4^(2-), CO_3^(2-), HCO_3^-, Cl^-` dissolved in it, it is called hard water.

The reason it is called hard because the cations undergo a displacement reaction to replace the `Na` or `K` part of the fatty acid salts with themselves. These new salts are generally insoluble in water, so it forms a precipitate. This hinders foam formation of the soap.

So, to make the water soft again, we need to go through some processes.

The Ion Exchange method is the most efficient of all other methods of Hardness removal. [It can remove both temporary and permanent hardness]

In the Ion Exchange method,

i) First the hard water is passed through the first resin, Cation Exchange Resin or Base - Exchange Resin. This resin is nothing
but a big organic molecule falling in the group of carboxylic acids or sulphonic acids. (`-COOH and -SO_3H`) When hard water passes through this, displacement reaction occurs and hardness causing cations get precipitated out.

`2R-COOH + (Ca^(2+), Mg^(2+), Fe^(2+)) rarr (Ca, Mg, Fe)R_2 + COOH^-`

`2R-SO_3H + (Ca^(2+), Mg^(2+), Fe^(2+)) rarr (Ca, Mg, Fe)R_2 + SO_3H^-`

ii) Cation free water goes out and enters the second resin chamber, Anion Exchange Resin or Acid - Exchange Resin This resin is also a big organic molecule falling in the group of Amines(`-NH_2`). These amines are basic in nature. It undergoes a displacement reaction in case of contact with the anions, and leaves a insoluble salt behind.

`R-NH_2 + H_2O rarr R-[NH_3^+ OH^-]`

`2R - [NH_3^+ OH^-] + SO_4^(2-) rarr (R-NH_3)_2SO_4 + 2OH^-`

iii) The water coming out of this chamber is deionized, not distilled. Even it contains nearly zero ions, it still contains germs and other organic materials.

To know how the Resins are regenarted, click here.

Hope this helps.