This method may be applied to absorption solutions containing more than 0.05 mg of cyanide. The method is not applicable if the absorption solution is coloured or highly turbid.
Principle :
Titration of the contents of the absorption vessel with silver nitrat solution, the silver ions, when in excess, forming a red silver complex with 5-(4-dimethylaminobenzylidine)rhodanine.
Reagents:
- Silver nitrate solution, c(AgNO3) = 0.01 mol/L
- Silver nitrate solution, c(AgNO3) = 0.001 mol/L
- Indicator solution, dissolve 0.02 g of 5- (4-dimethylamino benzylidine) rhodanine in acetone and dilute with acetone to 100 mL.
Equipments :
- Usual laboratoty equipment
- Magnetic stirrer, with bar
- Burette, of capacity 10 mL
- Titration vessels, made of glass, of capacity 50 mL.
Procedure:
Transfer the contents of the absorption vessel into a 50 mL beaker. Rinse the vessel three times with approximately 5 mL portions of water and add the rinsings to the beaker, add 0.1 mL of the indicator solution, immerse the tip of the burette containing the silver nitrate solution 0.001 mol/L in the solution, switch on the magnetic stirrer and titrate until the colour changes from yellow to red. Proceed similarly using the blank solution, the volume of the silver nitrate solution used in this blank test is usually 0.08 mL
Expression of result :
Total cyanide = (V1-Vo) x f1 x 1000 / f2 x Vs = mg/L
Vo = Is the Volume of silver nitrate solution required for the blank test., mL
V1 = Is the Volume of silver nitrate solution required for the titration, mL
Vs = Is the volume of the sample, mL
f1 = 0.052 the mass equivalent to 1 mL of 0.001 mol/l siver nitrate solution
f2 = 0.97as the volume of the sample is increased by addition after sampling.
Literature :
ISO 6703/1-1984 (E)
No comments:
Post a Comment