1) PH:-
PH = log10 [1/H+] mol/l
PH = - log10 [H+] mol/l
POH = - log10 [OH-] mol/l
Classification of water based on PH:
a) Neutral water
[H+] = [OH-] = 10-7 mol/l
PH = 7
POH = 7
b) Acidic water
[H+] > 10-7 mol/l PH < 7
[OH-] < 10-7 mol/l PoH > 7
c) Alkaline water
[H+] < 10-7 mol/l PH > 7
[OH-] >10-7 mol/l PoH < 7
Measurement of PH:
PH is exactly measured with Potentiometer and can approxly measured with help of Indicators.
An indicator is the substance which is either a weak acid or weak base which shows characteristic change in its color at a certain PH range.
Indicators are used to find-out the end points of Titration. The indicators which change their color in acidic range are called as "Acidic Indicators" and those which change their color in basic range are called "Basic Indicators".
Example: Methyl orange is an acidic indicator (PH = 4.5) and Phenolphalein is an Alkaline Indicator.
PH of drinking water is 6.5 to 8.5
Rejection is : Les than 6.5, and more than 9.5.
2)Alkalinity:-
The ability to neutralize ions present in water is called "Alkalinity". In natural water the following ions are responsible for major of the alkalinity and are called "Major Alkaline Species".
1) 0H - 2) co32- 3) HCO3 –
Following ions constitute a very small fraction of alkalinity and are referred as "Minor Alkaline Species".
1) HS - 2) NH3 3) HPO4- 4) H2PO4 - 5) H3SIO3 - 6) H2BO3 –
Note:-
The above 9 species (3-major and 6-minor) only can have ability to alkalinity such that they are called as Alkaline species.
IMPACTS OF ALKALINITY:-
1) Alkalinity imparts bitter taste to water.
2) Alkalinity forms precipitate of CaCO3 and Mg(OH)2 which causes deposition (or) Incrustation over pipes and other water treatment units.
3) HARDNESS:-
Hardness in water is the characteristic which prevents the formation of sufficient lather (or) foam with soap. It is caused due to multivalent metallic cations in water.
Ex:- Ca2+, Mg2+ , fe2+ etc.,
Note:-
Na+ also present in the water but it doesn't contribute hardness to water.
Types of Hardness:-
1) Carbonate hardness:-
Hardness due to Carbonates and Bicarbonates associated with multivalent metallic cations is referred as Carbonate Hardness. It is also called as Temporary Hardness as it can be easily removed by adding Lime.
2) Non carbonate Hardness :-
Hardness due to chlorides, Sulphates, Nitrates etc., associated with multivalent metallic cations is referred as Non Carbonate Hardness. It is also called as Permanent hardness as it can't be removed simply by boiling water or by adding lime. In order to remove permanent hardness following softening techniques are adopted.
a) Lime soda method
b) Zeolote/ Ion exchange method
c) Demineralization method
Impacts of Hardness in water :-
· Lesser foam formation there by increasing soap consumption
· If hardness is not present in water, it reduces the taste of food
· A certain amount of hardness is required for proper functioning of the body
· The hardness providing compounds such as Mgso4, Caso4 etc. produce laxative effect if present in excess.
Limits of Hardness:-
1) acceptable limit= 200 mg/l as Caco3
2) cause for rejection=600 mg/l as Caco3
3) Preferred limit=(75 to 115 mg/l as Caco3)
4) Dissolved Solids:-
This dissolved solids are measured either by Gravimetric method (or) Specific conductivity test.
The gravimetric method will give exact result where as the specific conductivity test will gives approximate method. In specific conductivity test, TDS is measured by determining electrical conductivity of water using Di Ionic water tester.
Limitation:- This test gives approx amount of TDS as the compounds which dissolved in water but do not get ionized can't be measured in this test like phenolic compounds, alkaholic compounds etc.,