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Determination of carbonates and bicarbonates from irrigation water sample.

Aim - 
Determination of carbonates and bicarbonates from irrigation water sample.


 In irrigation water important ions namely chloride, sulphates, nitrates, carbonates and bicarbonates are present .
some of the carbonates and bicarbonates ions constituted the total alkalinity of water.

Principle -
The Carbonate and Bicarbonate ions in the sample can be determined by titrating it against standard sulphuric acid using phenolphthalein and methyl orange indicator respectively .
addition of phenolphthalein gives pink red colour in presence of carbonates and titration with H2So4 converts this carbonates into bicarbonates and decolourise the pink red colour of the solution. 
In colourless solution methyl orange is added with gives yellow colour to the solution further titration against H2 s o4 neutralization of all bicarbonates and colour of solution changes from yellow to red orange. 

Reagents -
1 ) standard sulphuric acid (0.01 normality) -
 Take 0.28 ml H2 s o4 (36 normality) with atomic pipette and dilute to 1 litre distilled water. 
2) phenolphthalein.-
 Dissolved  0.25 gram pure phenolphthalein powder in 600 ml of 60% ethyl alcohol. (ethanol) 
3) Methyl orange -
Dissolve 0.5 gram dry methyl orange powder hundred ml of 95%.

Procedure  
Take 10 ml of water sample in hundred ml conical flask and dilute it by 25 ml distilled water . 

Add three drops of phenolphthalein, if pink red colour appears. It means carbonate are present titrate them against standard H2 s o4 pink colour disappear.

 The burette reading is designated as 'Y' ml , which is half of the carbonates present in the water. (2Y)  

To this colourless solution add three drops of methyl orange which gives yellow colour to the solution again titrate with standard H2So4 till colour changes from yellow to orange or Rose Red.

 Record the volume of H2So4 as  'Z'  ml.

1) carbonate -
Carbonates (mleq/lit) = 2Y × N.of H2so4 × 1000/volume of water sample. 

= 2Y × 0.01÷10
  × 1000

=2Y mleq/lit.

2) Bicarbonate -
Bicarbonate mleq/lit = (Z - 2Y) × N of H2So4 × 1000 / volume of water. 

=(Z-2Y) × 0.01 × 1000 ÷10

=(Z-2Y) × 10/10

= Z-2Y

Results 

The given water sample carbonates are present in ------mleq/lit and bicarbonate present in -------mleq/lit.

Rating for carbonate. 
<1.5.          Good quality water 
>1.5.          Bad quality water. 

Results 
Hence given water sample is --------(ratings) quality water. 

Rating for bicarbonate. 
<1.5.           Good quality water. 
1.5 to 8.       Medium quality water. 
>8.               Bad quality water. 

Results 
Hence given water sample is ------ (ratings) quality water. 


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