calculate the hardness of given sample of water, if 50 ml of sample water gives end point with 20 ml of EDTA solution. 20 ml of standard hard water of concentration 0.02N gives end point with 25 ml of EDTA solution
Answers
Answer:
Hardness of Water
Hardness of water is due to the presence of dissolved minerals of Ca2+, Mg2+
,
Al3+
, Iron and other heavy elements. Specifically due to Calcum Sulphate, Calcium
Bicarbonate, Calcium chloride, Magnesium Sulphate, Magnesium Bicarbonate and
Magnesium chloride.
It can also be defined as soap consuming capacity of water.
Soft water . Hard water
1. It readily lather with soap. It does not readily lather with soap.
2. It will not form insoluble scum It forms insoluble scum with soap.
with soap.
3. It does not affect the cleaning It affects the cleaning action of soap.
action of soap.
4. It does not contain dissolved It does contain dissolved salts of
salts of Ca and Mg. Ca and Mg.
Reaction with Soap
2 R-COONa + Ca2+
(RCOO)2 Ca + 2 Na+
(White insoluble scum)
2 R-COONa + Mg2+
(RCOO)2 Mg + 2 Na+
Scummy Precipitate
Temporary hardness (Carbonate hardness) is caused by the presence of
dissolved bicarbonates of Calcium, Magnesium, Iron and other heavy elements.
It can be eliminated by mere boiling.
Ca(HCO3)2
→ CaCO3↓ + H2O + CO2 ↑
Mg(HCO3)2
→ MgCO3 + H2O + CO2 ↑
MgCO3
→ Mg(OH)2↓ + CO2 ↑
Permanent Hardness (non-carbonate hardness) is due to the presence of
dissolved chlorides and sulphates of Calcium, Magnesium, Iron and other heavy
elements.
It cannot be eliminated by boiling.