The Breakpoint Experiment 3kj25

THE BREAKPOINT EXPERIMENT

First by iodometry (thiosulphate) method chlorine solution 1 Prepared from a source of chlorine such as calcium hypochlorite Ca(OCl)2 Take little amount of Ca(OCl)2 and dissolve it in appropriate amount of distillated water and let it to precipitate and take the clear solution . Sodium thiosulphate Na2S2O3 0.1 N , 0.025 N (2 Potassium dichromate K2Cr2O7 0.1 N (3 potassium iodide KI 5% or crystals(4 . ( Starch indicator (1 g in 100 ml distillated water (5 . : Procedure : i) Standardize thiosulphate by dichromate as the following , Add 10 ml of dichromate in conical flask , add about 1 gm KI crystals ml distillated water ,2 ml glacial acetic acid , stand for about 6 minutes , titrate 30, with thiosulphate solution until yellow color begin to pale add 1 ml of starch solution . and complete until blue color disappear ii) Standardize chlorine solution to strength 1 g/L. by the same way above replacing dichromate with chlorine solution .in the manner of 1ml = 1 mg Cl iii) Take about 10 conical flasks , fill it with 500 ml raw water and the doses of : chlorine as the following

Close the conical flasks with plaster and place it in dark place for the staying time of water in precipitation pool as calculated from equation : Staying time= Volume of precipitation pool / rate of pumped water Shake the flasks each 30 minutes distribute the dose in the entire volume : After the time ends titrate each conical flask with thiosulphate as the following Add 2 ml of glacial acetic acid , 1 g of KI to each flask, let stand for 6 minutes, titrate with thiosulphate solution until pale yellow then add 1 ml of starch solution and complete titration until blue color disappears : Calculations N*V)S2O3=(N'*V`)Cl) (N`=0.025*VS2O3 /500 …………….(1 Strength for Cl =N`*Eq.Wt VS2O3*35.5 /500

g/L *0.025 =

VS2O3*35.5*1000 /500

mg/L *0.025= Res Cl = VS2O3 *1.775 mg/L

: Record your data in table like this Series The dose of VS2O3 mL Cl mg/l Taken in titration 1 2 3 4 5 6 7 8 9 10

Res Cl = VS2O3*1.775 mg/L

:Draw a plot between the doses of Cl against the Res.Cl such as

sometimes break point curve appear as

the shape of the curve is differ from the conventional shape of break-point because of the trace amounts of ammonia

The first part of curve Res Cl appear as chloramines so if ammonia present in a trace amount the formation of chloramines decrease and one imagine the curve like straight line but the fact that break point greater than . the chloramine products and the point that the curve incline not be clear Whereas the Res.Cl at the breakpoint equals to 2.5 mg/L so the curve must appear .in the way that we see above