Hard Water

1
Hard Water
2
Clogged Pipes Hard Water
Step 1 Acid rain is formed
carbonic acid
Step 2 Acid rain dissolves limestone
limestone hard water
3
Pipes develop Scales
Step 3 Hard water is heated and deposits scales
Ca(HCO3)2 CaCO3(s) H2O
CO2 Mg(HCO3)2 MgCO3(s) H2O
CO2
D
scales on pipes
D
1 gram 1/7000th pound
300 gallons / day with 10 grain water supply
4
No More Hard Water Scale
No More Ugly Hard Water Spotting
Protects Plumbing and Appliances
Saves Money on Cleaning Products
5
Water Purification
Cation Exchanger
Anion Exchanger
Hard Water
Deionized Water
H
OH-
H
OH-
H
Mg2
OH-
Na
H
(a)
(b)
(c)
OH-
OH-
Fe3
H
Ca2
H
OH-
H
OH-
H
OH-
Hard water is softened by exchanging Na for
Ca2, Mg2, and Fe3.

• The cations in hard water are exchanged for H.
• The anions in hard water are exchanged for OH-.
• The H and OH- combine to give H2O.

Corwin, Introductory Chemistry 2005, page 361
6
Which ions are removed from hard water
to produce soft water?
Na(aq) H (resin) Na (resin)
H(aq)
Cl-(aq) (resin) OH (resin) Cl
OH-(aq)
Notice that the ion exchange resin produces both
hydrogen ions and hydroxide ions which can
readily combine to give water.
H(aq) OH- (aq) H2O (aq)
The net result is that the resin removes all ions
from water passing through the deionizing system.
Hard water is softened by exchanging Na for
Ca2, Mg2, and Fe3.
Corwin, Introductory Chemistry 2005, page 361
7
Calcium (Ca2) and Magnesium (Mg2) Ions
in Untreated Water
Sodium (Na1) Ions on beads
Calcium (Ca2) and Magnesium (Mg2) Ions on beads
Sodium (Na1) Ions in Treated Water