Chemical test
The following test are generally conducted to determine the chemical characteristics.
1.Total solids:
These includes the solids in suspension the colloidal dissolved form.The quality of suspended solids determined by the filtering the chemical test through a fine and then weighing the dry residue left.The quality of dissolved and collidial solids determined by the evaporation the filtered sample weighing the residiue include in the chemical test.
Sum of the suspended solids dissolved and collidial solids gives the value of the total solids by the chemical test.Total solids in which should be perfectably less than 500mg/1 and should be extended to 1000mg/1.To find the organic solids in the sample is evaporated first reduced weighed and then fused in muffle furnace.The organic matter is ignited leaving behind only organic matter.The difference between initial weight and the weight of in organic matter gives the weight of organic matter in the chemical test.
2.Hardness:
Certain material in water react with soap causing precipitation.This precipitated appears as scum.No lather can be formed until enough soap has been dissolved to react with all the material.This characteristics of water which prevents latherimg soap is called Hardness.Hardness is of two forms namely temporary hardness and permanent hardness.Temporary hardness is caused by bicarbonate of calcium and magnesium.It is removed by simple Boiling it is also known as carbonate hardness.Permanent hardness also called non-carbonate hardness is called by chlorides sulphate and nitrate of calcium and magnesium in the chemical test.
Harndess water consume more soap and hence not suitable for laundries.Hard water is also unit for usage of in boiler as it cause boiler scale.Hardness is expressed in ppm or mg/1 of calcium carbonate.Hardness can be found by soap test.The standard solutions is added in the sample of water and the mixture is agitated vigorously.Five minutes are allowed for lather formation the difference of total amount of soap solutions and lather factors gives the hardness but this test is now a day obsolete in the chemical test.
At present hardness generally determined by versenate method also called EDTA method which is by more accurate in this method the sample of water is titrated against EDTA or its sodium salts,until wine red colour change to blue.Eriochrome Black-T is used an indicator in the chemical test.
3.Chlorides:
Chlorides are present mostly in combination with sodium and to less extent with calcium and magnesium.These are most stable components water with excess of chlorides is not suitable for heart and kidney patients.The presence of chlorides may also be due to the mixing is sewage and saline water included in the chemical test.
The chlorides can be determined by titrating water with silver nitrate and potassium dichromate.The method is called Mohr's method in the chemical test.Chlorides content of treated water should not be exceeds 250mg/1.
4.Fluorides:
Fluorides may be occurring naturally in the water or may be present in water die to the pollution by the industry wastes.Flourides upto 1 mg/1 in drinking water is beneficial and safe as they reduce dental decay.But if the concentration exceeds 1.5mg/1 disfigured involving unsightly stabbing of teeth called "mottled"enmale of the teeth,or even skeletal damage in both children and adults called "fluorosis"are caused hence if it is necessary that fluorides level have to be closely controlled in the chemical test.
5.Dissolved gases:
a.oxygen: Presence of oxygen in dissolved from is necessary to keep it fresh.A minimum concentration of 4 to 5 mg/1 of D.O. is required in water for the sustenance of fish life.If D.O. is high it promotes corrosion of pipes.The quality of oxygen that the water can hold depends on the temperature my the test of chemical test.
A simple method to determine the D.O. is to expose water for 4 hours at a temperature of 27°c with 10% potassium permanganate.The quantity of oxygen absorbed then be calculated.Dissolved can also be found by Winkler method.Dissolved oxygen level in natural unpolluted water at normal temperature is found to be in the order of 10mg/1 in the chemical test.
Free ammonium indicated the first.stage of decomposition of organic matter suggesting that water is polluted recently.Albuminoid nitrogen indicates the presence of nitrogen before decomposition.The amount of nitrites present in water can be measured by colourmatic method for and napthamine and that for nitrate pheno-disulphonic and potassium hydroxide in the chemical test.
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