winkler test for dissolved oxygen
winkler test for dissolved oxygen
Does anyone have an 'easy recipe' for 'dissolved oxygen test.
Dissolved Oxygen using the Winkler Titration Method
Hi Lynda,
There are many Dissolved Oxygen Determination Tests, but for ease I will list one for you..
The Following method is a Modified Winkler Titration, It does work well to give good results considering it is a Titrimetric Determination.
Reagent List:
Manganous Sulfate 36% Solution (30mL);
Alkaline Potassium Iodide Solution, made by, Adding 1% Sodium Azide + 14% Potassium Iodide dissolve this in 60-70% Potassium Hydroxide Solution to make up to 100% and slowly dissolve this. (30mL)
Sodium Thiosulfate 0.4% solid in water to make to 100% (30mL)
Sulfuric Acid: 1 Part H2SO4 to 1 Part Water (30mL)
Starch Solution: 0.13% Salicylic Acid + 0.5% Soluble Starch, Distilled water to make to 100% (30mL)
All volumes of 30mL will not be used at once, allowing for further determinations at a later date.
Once the reagents have been organised and made we can move on to the next step.
Equipment Needed:
60mL glass bottle with Screw Cap Lid;
10mL Syringe;
30mL vial with a snap lock lid with a small hole at the top (to put the syringe through) a graduation mark at 20mL needs to be marked on the vial also.
Method:
1. Obtain the water to be tested in the 60mL glass bottle with the screw cap lid, filling the bottle until there is about 10mL of space left in the top. Quickly cap this to prevent any O2 becoming dissolved during the process.
Do not shake the bottle at this stage of the Analysis..
2. Add to this solution whilst in the glass bottle 8 drops of Manganous Sulfate which has been freshly prepared via a dropper bottle.
3. To this solution, add 8 drops of Alkaline Potassium Iodide.
4. Recap the bottle and invert several time SLOWLY and GENTLY.
5. Stand the bottle to allow for a brown precipitate to fall out of solution. (This should be complete in approx 5 mins).
6. After the precipitate has settled to the bottom of the bottle, add 8 Drops of the 1:1 Sulfuric Acid.
7. Recap and Gently invert again to dissolve the precipitate.
8. Fill the 30mL vial to the 20mL graduation mark with this solution (Should be a clear brown colour) and cap it with the snap on lid.
9. Fill the syringe with 1mL of the Sodium Thiosulfate solution (keeping in mind that 1mL is equivalent to 10mg of Sodium Thiosulfate).
10. Insert the syringe into the hole in the cap of the vial.
11. Press the plunger of the syringe to only allow one drop at a time to enter.
12. During each drop swirl vigorously to mix the solution.
13. Repeat this until the solution turns a pale yellow.
14. When this occurs add 8 drops of the starch solution which then causes the solution to turn a deep blue colour.
15. Continue adding the Sodium Thiosulfate solution whilst stirring until the end point is reached. This is noticed as the solution becomes clear.
16. Read the volume used from the syringe of Sodium Thiosulfate.
This value is equivalent to mg/L of Dissolved Oxygen in the Water.
I hope this helps...
There are many Dissolved Oxygen Determination Tests, but for ease I will list one for you..
The Following method is a Modified Winkler Titration, It does work well to give good results considering it is a Titrimetric Determination.
Reagent List:
Manganous Sulfate 36% Solution (30mL);
Alkaline Potassium Iodide Solution, made by, Adding 1% Sodium Azide + 14% Potassium Iodide dissolve this in 60-70% Potassium Hydroxide Solution to make up to 100% and slowly dissolve this. (30mL)
Sodium Thiosulfate 0.4% solid in water to make to 100% (30mL)
Sulfuric Acid: 1 Part H2SO4 to 1 Part Water (30mL)
Starch Solution: 0.13% Salicylic Acid + 0.5% Soluble Starch, Distilled water to make to 100% (30mL)
All volumes of 30mL will not be used at once, allowing for further determinations at a later date.
Once the reagents have been organised and made we can move on to the next step.
Equipment Needed:
60mL glass bottle with Screw Cap Lid;
10mL Syringe;
30mL vial with a snap lock lid with a small hole at the top (to put the syringe through) a graduation mark at 20mL needs to be marked on the vial also.
Method:
1. Obtain the water to be tested in the 60mL glass bottle with the screw cap lid, filling the bottle until there is about 10mL of space left in the top. Quickly cap this to prevent any O2 becoming dissolved during the process.
Do not shake the bottle at this stage of the Analysis..
2. Add to this solution whilst in the glass bottle 8 drops of Manganous Sulfate which has been freshly prepared via a dropper bottle.
3. To this solution, add 8 drops of Alkaline Potassium Iodide.
4. Recap the bottle and invert several time SLOWLY and GENTLY.
5. Stand the bottle to allow for a brown precipitate to fall out of solution. (This should be complete in approx 5 mins).
6. After the precipitate has settled to the bottom of the bottle, add 8 Drops of the 1:1 Sulfuric Acid.
7. Recap and Gently invert again to dissolve the precipitate.
8. Fill the 30mL vial to the 20mL graduation mark with this solution (Should be a clear brown colour) and cap it with the snap on lid.
9. Fill the syringe with 1mL of the Sodium Thiosulfate solution (keeping in mind that 1mL is equivalent to 10mg of Sodium Thiosulfate).
10. Insert the syringe into the hole in the cap of the vial.
11. Press the plunger of the syringe to only allow one drop at a time to enter.
12. During each drop swirl vigorously to mix the solution.
13. Repeat this until the solution turns a pale yellow.
14. When this occurs add 8 drops of the starch solution which then causes the solution to turn a deep blue colour.
15. Continue adding the Sodium Thiosulfate solution whilst stirring until the end point is reached. This is noticed as the solution becomes clear.
16. Read the volume used from the syringe of Sodium Thiosulfate.
This value is equivalent to mg/L of Dissolved Oxygen in the Water.
I hope this helps...
Dr Robert Crosdale. MRACI. NSS. NSSA. NASA.
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
Ph.D (Chem), Post Grad Ph.D (Physics), M.Ed, B.Sc (Hons), Dip. Appl. Sc. (Chem)
Lake Munmorah High School.
University of New England.
University of New South Wales.
University of Newcastle.
To understand the Universe from our perspective, we need to look towards our own backyard first for answers.
** AD ASTRA PER ASPERA - SEMPER EXPLORO **
