Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
Title: HARD AND SOFT WATER
Description: It describes hard and soft water. The formation, and the processes they undergo
Description: It describes hard and soft water. The formation, and the processes they undergo
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
4/2/2012
Hard water
• Hard water is the type of water that has high
mineral content (in contrast with soft water)
...
• Calcium usually enters the water as either
calcium carbonate (CaCO3), in the form of
limestone and chalk, or calcium sulfate (CaSO4),
in the form of other mineral deposits
...
• Hardness in water can cause water to form scales
and a resistance to soap
...
• The predominant source of magnesium is
dolomite [CaMg(CO3)2]
...
• The total water 'hardness' (including both Ca2+
and Mg2+ ions) is read as parts per million (ppm)
or weight/volume (mg/L) of calcium carbonate
(CaCO3) in the water
...
• It can be removed by boiling the water or by
the addition of lime (calcium hydroxide)
...
• The following is the equilibrium reaction when
calcium carbonate (CaCO3) is dissolved in water:
• CaCO3(s) + H2CO3(aq) ⇋ Ca2+(aq) + 2HCO3-(aq)
• Boiling the water will remove hardness as long as
the solid CaCO3 that precipitates out is removed
...
5
Permanent hardness
6
Permanent hardness
• Permanent hardness is hardness (mineral
content) that cannot be removed by boiling
...
• Permanent hardness can be removed using a
water softener or ion exchange column, where
the calcium and magnesium ions are exchanged
with the sodium ions in the column
...
• This is also known as limescale
...
• This unit uses sodium chloride (table salt) to
recharge beads made of the ion exchange
resins that exchange hardness mineral ions for
sodium ions
...
• This process is called ion exchange
...
• Calcium bicarbonate, often present in temporary
hard water, may be boiled in a kettle to remove
the hardness
...
• This scale is composed of calcium carbonate
...
• This process involves the addition of slaked
lime (calcium hydroxide Ca(OH)2) to a hard
water supply to convert the hydrogen
carbonate hardness to carbonate, which
precipitates and can be removed by filtration:
• Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O
• The addition of sodium carbonate also
permanently softens hard water containing
calcium sulfate, as the calcium ions form calcium
carbonate which precipitates out and sodium
sulfate is formed which is soluble
...
• Sodium sulfate has no effect on the hardness of
water
...
• Negatively-charged resins absorb and bind
metal ions, which are positively charged
...
• As the water passes through the resin column,
the hardness ions replace the hydrogen,
sodium or potassium ions which are released
into the water
...
15
16
4
4/2/2012
Ion-exchange resin
Disadvantages of Hard Water
• Resins are also available to remove carbonate,
bi-carbonate and sulphate ions which are
absorbed and hydroxyl ions released from the
resin
...
(1) metal ions react with soaps and calciumsensitive detergents, hindering their ability to
lather and forming a precipitate
2C17H35COONa + Ca2+ → (C17H35COO)2Ca + 2Na+
• Presence of "hardness ions" also inhibits the
cleaning effect of detergent formulations
17
Disadvantages of Hard Water
18
Disadvantages of Hard Water
(2) calcium and magnesium carbonates tend to
precipitate out as hard deposits to the surfaces of
pipes and heat exchanger surfaces
...
• In boilers, the deposits act as an insulation that
impairs the flow of heat into water, reducing the
heating efficiency and allowing the metal boiler
components to overheat
Title: HARD AND SOFT WATER
Description: It describes hard and soft water. The formation, and the processes they undergo
Description: It describes hard and soft water. The formation, and the processes they undergo