Water always contains some quantity H^+ hydrogen ions and hydroxyl ions ОН^-. If it is more ions of hydrogen, water gains acid character if the hydroxyl ions, then alkaline is more. For assessment of degree of acidity of water solution there is a pH value. It is in number equal to a negative decimal logarithm of activity of hydrogen ions, unit of its dimension – mol/litre. That is rn = - lg [H^+]. Size rn fluctuates from 0 to 14. If it less than 7, solution sour. Respectively, if more than 7 – alkaline.
It is required to you
- - indicator pieces of paper;
- - laboratory pipette or plastic tubule;
- - transparent capacity;
- - indicator substances;
- - pH-meter.
Instruction
1. There is a fast and simple, though not really exact way of determination of acidity of water – by means of indicator pieces of paper (strips). They can be bought in shops of chemical reactants or to get in laboratories. On packing there is always a reference scale of comparison where to each value of size rn there corresponds a certain coloring – from cherry-burgundy (the silnokisly environment, rn =0) to dark blue (the silnoshchelochny environment, rn = 14).
2. To define acidity of water, it is necessary to apply by means of the laboratory pipette or a plastic tubule one drop on an indicator strip. As a last resort, just dip a strip tip into water. Then quickly compare the formed coloring to a reference scale. The strip will not change color only when rn waters it is close to a neutral indicator (7.0).
3. If there are no such pieces of paper (strips), it is possible to use solutions of indicators. From a school course of chemistry names are for certain familiar to you: litmus, methyl orange, phenolphthalein.
4. Pour water in transparent tanks, add to everyone a little indicator substance. Then estimate coloring change. Litmus in acidic environment accepts red color, and in alkaline – blue. Phenolphthalein in the alkaline environment becomes bright crimson. Methyl orange in the silnokisly environment accepts red color, and in the subacidic environment becomes yellow. Certainly such way is suitable only for determination of nature of the environment of water solution. About any exact value rn here out of the question.
5. It is most precisely possible to determine an indicator rn (that is acidity level) by special devices – rn-meters. They are issued in very wide assortment. There are simple, compact rn-meters which can be used literally anywhere, is very difficult and expensive which use only in laboratories. The principle of operation of such devices is based on measurement of electric potential of an electrode of the comparison shipped in the studied solution.