Requirements-
- Water sample
- Watch glass
- pH indicator paper
Principle-
pH used as
hydrogen ion concentration of natural water. It is an important physical factor.
The pH of water is defined as the logarithm of the reciprocal of hydrogen ion
concentration. It may be expressed mathematically as below-
pH = log 1/H+
pH =
log [1/H+]
where,
H+
is the amount of hydrogen ion in solution (mol/l). There is 0.601 of hydrogen
ions and a corresponding quantity of OH- ion in a liter of pure
water.
The pH of
neutral water is 7. Increase in the concentration of H+ ion results
in a lower pH value (acidic medium) or reduction in H+ ion concentration
brings about higher + value alkaline medium. Solution are acidic in pH value below 7 and
alkaline in value above 7. Any addition of even a trace of acid or base disturb
the pH value of distilled water of neutral salts. In buffering system, the pH
is determined by the relationship between CO2 and CO3 or
by H+ ion arising from dissociation of H2CO3
and OH- ion arising from hydrolysis of HCO3.
Procedure-
Water sample
is taken in a watch glass and small strip of pH indicator paper was drop in the
water after few minutes, permanent color appeared which was observed and method
will be prescribed universal indicator disk.
Calculation-
S.No. Water sample pH Value Medium
1. Pond water 7.5 alkaline
2. Borewell 6.8 acidic
3. Dug well 7.3 alkaline
4. Tap water 6.6 acidic
Precaution-
- Handling of the paper with dry hand
- Observation of pH carefully without disturbing sample water
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