Softening

Question 1

Exam question

Explain briefly the objectives of softening and how the processes by which softening may be achieved

Answer 1

Softening is the process by which hardness is removed from water, hardness is due to the presence of divalent metallic cations of calcium and magnesium. Ca and Mg are present in the form of carbonates and bicarbonates ( carbonate hardness) and in the form of sulfates and chlorides (non carbonate hardness).
Processes by which softening may be achieved:
Lime-Soda ash process:
1)Uses lime (CaO/Ca(OH)2 and soda ash (Na2CO3)
2) Lime removes carbonate hardness and soda ash removes non-carbonate hardness from water.
3-) Hardness is removed as calcium carbonate (CaCO3) and Magnesium Hydroxide (Mg(OH)2) precipitates.

Ion exchange process
Ions are removed by interchange with other ions that are immobilized within a solid matrix for example sodium-based resin in which the sodium ions are replaced by the divalent ions Ca and Mg.

Question 2

Review reactions and slides ( more info exist)

Answer 2

check

Question 3

In noncarbonate hardness, MgSO4 is removed by

Answer 3

first by addition of Ca(OH)2 to form CaSO4 then we add Na2CO3

Question 4

CaCl2 is removed by

Answer 4

addtion of Na2CO3

Question 5

MgCl2 is removed by

Answer 5

addition of Ca(OH)2 to form CaCl2 then we add Na2CO3