S.R.M NAGAR, KATTANKULATHUR 603 203 Department of Chemistry (2015-2016) GE 6163 – CHEMISTRY LAB MANUAL
Step I : Standardization of sodium thiosulphate Titration I (Standard dichromate vs Sodium thiosulphate) Burette reading (ml) Sl.No Volume of Potassium dichromate (ml) 1 20 0 2 20 0 3 20 0 Initial Final Volume of Potassium dichromate (V1) 20 ml Strength of Potassium dichromate (N1) 0.0125 N Volume of Sodium thiosulphate (V2) ml Strength of Sodium thiosulphate (N2) N According to volumetric formula V1N1 N2 Strength of Sodium thiosulphate (N2) V2N2 V1N1 V2 N Volume of Sodium thiosulphate (ml) Indicator V1 Starch
1. ESTIMATION OF DISSOLVED OXYGEN OF BOILER FEED WATER Expt. No. Date AIM To determine the dissolved oxygen in the boiler feed water. CHEMICALS REQUIRED Na2S2O3 (N/40), MnSO4 solution, KI, starch, conc. H2SO4 PRINCIPLE Oxygen dissolves in water to the extent of 7 - 9 mgs/lit at a temperature range of 25 35 C.The estimation of dissolved oxygen in water is useful in studying water pollution. Water sample is collected carefully avoiding aeration/deaeration in ground stoppered flask. Initially manganous sulphate and alkali-iodide reagents are added and the reaction occur as follows Mn2 Mn OH 2 2OH 1 2 Mn OH O2 2 MnO OH 2 White Yellow brown Potassium iodide and the precipitate react with concentrated sulphuric acid liberating iodine and the liberated iodine is titrated against Na2S2O3 MnO OH 2 2H2SO4 Mn SO4 2 2KI 2Na2S2O3 Mn SO4 2 MnSO4 I2 Na2S4O6 3H2O K2SO4 I2 2NaI PROCEDURE Titration I Standardisation of sodium thiosulphate The burette is washed and rinsed with sodium thiosulphate solution. Then the burette is filled with the given sodium thiosulphate solution. 20 ml of 0.0125N potassium dichromate solution is pipetted out into a clean conical flask. To this, 5 ml of sulphuric acid and 50 ml of 5% potassium iodide are added. This is titrated against sodium thiosulphate solution. When the solution becomes straw yellow colour, starch indicator is added and then titration is continued. The end point is disappearance of blue colour and appearance of light green colour. The titration is repeated to get concordant values.
Step II : Estimation of dissolved oxygen Titration II (Water sample vs Sodium thiosulphate) Burette reading (ml) Sl.No Volume of Potassium dichromate (ml) 1 20 0 2 20 0 3 20 0 Initial Volume of Sodium thiosulphate (ml) V2 Final Starch Volume of Sodium thiosulphate (V1) Strength of Sodium thiosulphate (N1) Volume of water sample (V2) 100 ml Strength of water sample N2 N According to volumetric formula V1N1 V2N2 V1N1 V2 N2 Amount of dissolved oxygen in one litre of tap water = Normality Eq.wt.of O2 Indicator 1000 mg. N 8 mg lit 1000