a. Aim: Estimation of dissolved oxygen in given sample of water.
b.
Principle: Oxygen combines with manganous hydroxide to form
higher hydroxide, which on acidification liberate iodine equivalent to that of
oxygen fixed. This iodine is titrated by standard sodium thiosulphate solution
in presence of starch as indicator.
c. Material Required: Potassium iodide (700g in 1 liter), mangnous sulphate (480g in 1 liter), sodium thiosulfate (0.025N), Starch Indicator (1%), sulphuric acid (Concentrated), conical flask, beaker, titration burette.
d.
Procedure: Collect water sample in 250ml sampling bottle, add 2ml
of manganous sulphate and alkaline iodide (potassium iodide) solution each at
the bottom of bottle and place the stopper. Mix the sample by turning the
bottle up and down. The brownish precipitate settles at the bottom. Then add 2 ml
of concentrated H2SO4 and shake the bottle to dissolve
the precipitate. Transfer 50ml of solution to a conical flask, titrate it
against the thiosulphate solution. Titrate until the solution turns straw
yellow in colour and add 2-4 drops of freshly prepared starch indicator, the
solution colour changes to blue. Continue with the titration until the
disappearance of blue colour.
Calculation: Dissolved oxygen (mg/l) =
8=
Equivalent weight of oxygen
V=
Volume of titrant
Vs=
Sample volume
No comments:
Post a Comment