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How to measure the hardness of the water

How to measure the hardness of the water

Water is said to be rigid if it contains large amounts of magnesium and calcium salts.

Such water in everyday life usually do not like because of the fact that it forms a layer of scum on the kettles and pans and makes the soap foam.

You will need

  • Methodical edition of Analytical Chemistry.



Rigidity Water is of two kinds: carbonate (temporary) and non-carbonate (permanent). First it removed by boiling (about an hour). Thereafter, a white precipitate (calcium carbonate) and carbon dioxide. The second eliminates complicated: either chemically or by distillation. The total hardness of water is determined by the sum of the permanent and temporary hardness. In chemistry stiffness express the sum of milliequivalents of calcium and magnesium ions in 1 liter of water. One milliequivalent is equal stiffness 20.04 milligrams of calcium or magnesium ions 12.16 milligrams in 1 liter of water.


One method of measuring the hardness - titration. It is necessary to conduct a two conical flasks placed 100 ml test liquid, 5 ml of buffer solution, 1 ml of sodium sulfide and 5-6 drops of indicator chromogen black ET-00 (measuring pipette should be used). After stirring the solutions have a pink color.


The mixture was then titrated with Trilon BUsing microburet. Trilon B is added carefully, drop by drop, until the blue color. It is further noted how many ml of Trilon B went on titration to two decimal places. Two samples titrated for the purity of the experiment.


The next step is considered to be the average volumeusing a simple formula Vav = (V1 + V2) / 2, where V1 - volume Trilon B poshedshego the titration solution in the first flask ml, V2 - volume Trilon B poshedshego the titration solution in the second flask. And the last thing to do in this method - is to calculate the stiffness of the formula F = (Vav * N * 1000) / V, where Vav - average amount of Trilon B, who had gone on titration in two flasks ml (counted by the above formula) of n - normal concentration of Trilon B, 1000 - per 1 liter of water, the V - the volume of the test water, ml. If necessary rigidity express in degrees, the resulting number is multiplied by the coefficient of 2.8.


When the rigidity of up to 4 mEq / L of water is consideredsoft, 4 to 8 mEq / l of medium hardness, 8 to 12 mg - equivalent / liter and rigid than 12 mEq / l particularly rigid. Of course, in modern laborotorii water hardness can be measured not only by titration, but also various devices such as electronic devices and a conductivity meter. If you have the opportunity to work on such equipment, it is easier, more efficient and more accurate. But titration method is accurate enough and simple.

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