Determination of Hardness in Water
Serina Pooja Sowman | Practical 7: Determination of Hardness in Water | | | | | 10/3/2012 | |
Aim:
To determine the different types of hardness and alkalinity found in the water by titration methods. This is used to calculate the concentrations of calcium and magnesium found in the water.
Principles:
The hardness of water is determined to provide a measure of the quality of water for household and industrial use. Hard water is not a health hazard. Drinking hard water contributes a small amount of calcium and magnesium towards humans dietary needs.
Hard water is caused by metal ions (salts) being dissolved in the ground water. We measure hardness in water in terms of CaCO3 as the Ca2+ ion is greater than the concentration of any other metal.
Hard water does cause soap scum, clog pipes and clog boilers. Soap scum is formed when the calcium ion binds with the soap. This causes an insoluble compound that precipitates to form the scum you see. Soap actually softens hard water by removing the Ca2+ ions from the water. When hard water is heated, CaCO3 precipitates out and then clogs pipes and industrial boilers. This leads to malfunction or damage and is expensive to remove. [1]
The reaction that takes place from the insoluble calcium carbonate:
CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)2(aq)
This reaction is reversible on heating. This removes the temporary hardness.
Temporary hardness is caused by the presence of dissolved calcium and magnesium compounds. The reactions that take place between EDTA and the metal cations:
Ca2+ + H2Y2- → CaY2- + 2H+
Mg2+ + H2Y2- → MgY2- + 2H+
Mg-EBT- + H2Y2- → MgY2- + HEBT- + H+
Permanent hardness is caused by the presence of calcium and magnesium sulphates and chlorides. The water sample must be boiled to determine the permanent hardness as the compounds (CaSO4 and MgSO4) are not affected by heating and remain in the water sample. Boiling only removes the temporary hardness.
Alkalinity of the
Aim:
To determine the different types of hardness and alkalinity found in the water by titration methods. This is used to calculate the concentrations of calcium and magnesium found in the water.
Principles:
The hardness of water is determined to provide a measure of the quality of water for household and industrial use. Hard water is not a health hazard. Drinking hard water contributes a small amount of calcium and magnesium towards humans dietary needs.
Hard water is caused by metal ions (salts) being dissolved in the ground water. We measure hardness in water in terms of CaCO3 as the Ca2+ ion is greater than the concentration of any other metal.
Hard water does cause soap scum, clog pipes and clog boilers. Soap scum is formed when the calcium ion binds with the soap. This causes an insoluble compound that precipitates to form the scum you see. Soap actually softens hard water by removing the Ca2+ ions from the water. When hard water is heated, CaCO3 precipitates out and then clogs pipes and industrial boilers. This leads to malfunction or damage and is expensive to remove. [1]
The reaction that takes place from the insoluble calcium carbonate:
CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)2(aq)
This reaction is reversible on heating. This removes the temporary hardness.
Temporary hardness is caused by the presence of dissolved calcium and magnesium compounds. The reactions that take place between EDTA and the metal cations:
Ca2+ + H2Y2- → CaY2- + 2H+
Mg2+ + H2Y2- → MgY2- + 2H+
Mg-EBT- + H2Y2- → MgY2- + HEBT- + H+
Permanent hardness is caused by the presence of calcium and magnesium sulphates and chlorides. The water sample must be boiled to determine the permanent hardness as the compounds (CaSO4 and MgSO4) are not affected by heating and remain in the water sample. Boiling only removes the temporary hardness.
Alkalinity of the
References: http://homepages.ius.edu/DSPURLOC/c121/week13.htm [1] http://www.s-mart.se/blogs/2009/11/17/chem0120-determination-of-water-hardness-using-e-d-t-a/