Water is called hard if it contains a large amount of magnesium and calcium salts.
Such water in everyday life is usually very disliked because it forms a layer of scale on kettles and pots and does not allow the soap to foam.
You will need
- Methodical publication on analytical chemistry.
Rigidity There are two types of water: Carbonate (temporary) and non-carbonate (constant). The first is removed by boiling (about an hour). After that, a white precipitate (calcium carbonate) and carbon dioxide are formed. The second is eliminated more difficult: either chemically or by distillation. The total hardness of water is determined by the sum of the constant and time rigidity. In chemistry, the stiffness is expressed by the sum of milliequivalents of calcium and magnesium ions per liter of water. One milliequivalent of rigidity is equal to 20.04 milligrams of calcium ions or 12.16 milligrams of magnesium ions per 1 liter of water.
One way to measure stiffness is titration. To carry it out, two 100 ml of test water, 5 ml of buffer solution, 1 ml of sodium sulfide and 5-6 drops of the black ET-00 chromogen indicator should be placed in two conical flasks (measuring pipettes must be used). After mixing, the solutions are pink.
The resulting mixture is then titrated with Trilon B,Using a microburette. Trilon B is added carefully, by droplets, until a blue color is obtained. Further it is noted how many ml Trilon B went to titration to the nearest hundredth. Two samples are titrated for the purity of the experiment.
The next step is the average volume,Using the simple formula Vcp = (V1 + V2) / 2, where V1 is the volume of Trilon B, which went to titration of the solution in the first flask, ml, V2 is the volume of Trilon B, which went to titrate the solution in the second flask. And the last thing to do in this method is to calculate the stiffness by the formula Ж = (Vср * N * 1000) / V, where Vср - the average volume of Trilon B, which went to titration in two flasks, ml (calculated according to the above formula), N - normal Trilon concentration B, 1000 - recount per 1 liter of water, V - volume of water under study, ml. If it is necessary to express the rigidity in degrees, then the resulting number should be multiplied by a factor of 2.8.
At a hardness of up to 4 mEq / L, water is consideredSoft, 4 to 8 meq / l medium hardness, 8 to 12 mg-eq / l hard and more than 12 meq / liter extremely hard. Of course, in the modern laboratory, the water hardness can be measured not only by titration, but also by various instruments, for example, conductometers and electronic devices. If it is possible to work on such equipment, then it is easier, more efficient and more accurate. But the titration method is quite accurate and simple.