Thursday, February 2, 2012

Sulphate ions!

I always love the way my mam teaches me. Today we did "Estimation of Sulphate ions by nephlometry".
Mam started with a question "Why to estimate sulphate ion?". The question is so simple. But., as usual most members of the class blinked. Here we go and get to know why? :

Estimation of sulphate ions is important for two  reasons:
1) Sulphate ions causes SCALING in boilers, fermenters etc.,
2) Must be in a limited amount in drinking water.

Notes: 

Aim:
To determine the amount of sulphate ions present in the given sample.

Principle: 
Sulphates occur in water naturally as a result of leaching from gypsum and other common minerals. In addition, sulphate may be added to water by waste water treatment plant. The presence of sulphate is limited to 250ppm. Sulphate ions are precipitated as various sulphate crystal in acid medium. Light scattered by the solution is proportional to the concentration of sulphate ions which is measured in a nephlo turbidity meter.

Barium chloride + Sulphate ---> Barium sulphate + 2 chlorine

Reagents :

1) Anhydrous sodium sulphate :
148mg of sodium sulphate was dissolved in 100ml of distilled water. (100ml contains 100mg of sulphate)

2) Conditioning reagent

Procedure: 
10ml of stock solution was pipetted out into a 100ml of standard measuring flask and made upto the mark.
2, 4, 6, 8, 10 ml of working standard solution was pipetted and made upto 20ml with distilled water. 1ml
of conditioning reagent was added and 0.1g of barium chloride was added. The mixture was stirred using magnetic stirrer for a minute. The nephlometer was standardised with sodium sulphate solution. The unknown solution was prepared on the same way and Nephlo Turbidity Units were measured.

A calibration graph was drawn with concentration in x-axis and NTU in y-axis. The concentration of sulphate ions present in the given sample was determined from the graph.

Tabulation : 


Volume of working standard (ml)
Volume of water added (ml)
Concentration of sulphate ions (micro grams)
Volume of conditioning reagent added
Amount of  barium chloride added (mg)

    
       NTU
Blank
20
-----




     1ml




     100

0
2
18
200
45
4
16
400
103
6
14
600
169
8
12
800
182
10
10
1000
251
Unknown 20ml
(tap water)
---------------
      ???
190




 Calculation : 

Stock standard: 100ml contains 100mg of sulphate ions.
Working standard: (1 in 10 dilution)
1ml contains 0.1mg of sulphate.
2ml ---> 200 micrograms
4ml ---> 400 micrograms
6ml ---> 600 micrograms
8ml ---> 800 micrograms
10ml --> 1000 micrograms

Result: 

A Graph was plotted with the above readings and the Concentration of sulphate in the tap water was found to be 760 micrograms / 20 ml 


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