Thursday, October 25, 2007
Monday, October 22, 2007
DETERMINATION OF NITRATE IN RAW AND PORTABLE WATER
NOTE: TEST 2 date : 8,November, 2007
PRINCIPLE.
Nitrate reacts with sodium salicylate under strongly acidic conditions. Addition of excess sodium hydroxide solution produces the sodium salt of the organic nitro complex. This nitro compound is soluble in water and produces a strong yellow solution. The intensity of the color is proportional to the amount of nitrate in the sample and is measured at 410 nm on a spectrophotometer. A calibration graph relates absorbance to nitrate concentration.
RANGE
0 – 80 mg/l using a 5 ml aliquot of sample. The range may be extended by taking a smaller sample volume or by diluting the sample.
REAGENTS
Sodium salicylate (0.5 % w/v).
Dissolve 0.5 0.01g of laboratory reagent grade sodium salicylate in 100 ml of distilled water. Store in a cool place but prepare every 10 days.
Sodium hydroxide (25 % w/v).
Dissolve 25 0.1g of sodium hydroxide (NaOH) in 70 ml of distilled water. When cool, dilute to 100 ml with distilled water
Sulphuric acid (Concentrated). Analar grade S.G. 1.84
Standard Nitrate (stock) solution 1 ml = 500 g NO3.
Dissolve 0.815 0.001g of Analar potassium nitrate previously dried at 110oC in approximately 100 ml of distilled water. Quantitatively transfer to a 1000 ml volumetric flask and dilute to the mark with distilled water. Mix well.
Standard Nitrate (working) solution (A), 1 ml = 50 g NO3.
Pipette 10.0 ml of standard nitrate (stock) solution into a 100 ml volumetric flask, dilute to the mark with distilled water. Mix well.
Standard Nitrate (working) solution (B), 1 ml = 5 g NO3.
Pipette 10.0 ml of standard nitrate working solution ‘A’ into 100 ml volumetric flasks, dilute to the mark with distilled water. Mix well.
APPARATUS
Water bath
UV/visible range spectrophotometer.
General laboratory glassware.
Calibration procedure
Into a series of 100 ml pyrex beakers, dispense using a micro-burette the volume of standard nitrate working solutions shown in the table below;
Vol. of standard nitrate (working solution in ml) wt NO3 (g) Measure in the following size cell (mm)
SOLUTION (B)
0.00 0 (Blank) 40
1.00 5 40
2.00 10 40
5.00 25 40
10.00 50 40
SOLUTION (A)
2.00 100 10
4.00 200 10
6.00 300 10
8.00 400 10
Continue as under procedure 6.2 to 6.7
For each size cell, construct a calibration graph relating absorbance to weight of nitrate.
PROCEDURE
Pipette 5.00 ml of sample into 100 ml pyrex beaker. If more than 80 mg/l nitrate is expected, pipette a smaller aliquot or dilute sample accordingly. Note sample volume (v) used and dilution (d).
Add using a pipette, 2.0 ml of sodium salicylate solution (0.5% w/v). Mix well and evaporate to dryness on a water bath.
Remove from water bath and add using a pipette and safety pipette filler 1.0 ml of concentrated sulphuric acid. Mix well and allow to stand for 10 minutes.
Dilute to approximately 50 ml with distilled water.
Add using a measuring cylinder 10 ml of sodium hydroxide solution (25 % w/v). Mix thoroughly.
When cool, quantitatively transfer the solution to a 100 ml volumetric flask and dilute to the mark with distilled water. Stopper and mix well.
Measure the absorbance on a spectrophotometer against the blank (100 % transmission) in either a 10 mm cell or 40 mm cell at a wavelength of 410 nm: note the reading
If it is thought that a significant error may be introduced by color or turbidity in the sample, a duplicate sample should be treated exactly as under 6.1 to 6.7 but omitting the addition of the sodium salicylate solution, Step 6.2. Subtract the absorbance of this solution from that obtained for the sample to which salicylate solution has been added.
CALCULATION
Select the calibration graph for the size of cell used and read- off the weight of nitrate present in the solution.
Nitrate content
g NO3 * d/ v mg/l
Where v = sample volume (ml) used and
d = dilution where appropriate.
For nitrate concentrations up to 10 mg/l, report to nearest 0.1 mg/l, above 10 mg/l, report to nearest mg/l.
PRINCIPLE.
Nitrate reacts with sodium salicylate under strongly acidic conditions. Addition of excess sodium hydroxide solution produces the sodium salt of the organic nitro complex. This nitro compound is soluble in water and produces a strong yellow solution. The intensity of the color is proportional to the amount of nitrate in the sample and is measured at 410 nm on a spectrophotometer. A calibration graph relates absorbance to nitrate concentration.
RANGE
0 – 80 mg/l using a 5 ml aliquot of sample. The range may be extended by taking a smaller sample volume or by diluting the sample.
REAGENTS
Sodium salicylate (0.5 % w/v).
Dissolve 0.5 0.01g of laboratory reagent grade sodium salicylate in 100 ml of distilled water. Store in a cool place but prepare every 10 days.
Sodium hydroxide (25 % w/v).
Dissolve 25 0.1g of sodium hydroxide (NaOH) in 70 ml of distilled water. When cool, dilute to 100 ml with distilled water
Sulphuric acid (Concentrated). Analar grade S.G. 1.84
Standard Nitrate (stock) solution 1 ml = 500 g NO3.
Dissolve 0.815 0.001g of Analar potassium nitrate previously dried at 110oC in approximately 100 ml of distilled water. Quantitatively transfer to a 1000 ml volumetric flask and dilute to the mark with distilled water. Mix well.
Standard Nitrate (working) solution (A), 1 ml = 50 g NO3.
Pipette 10.0 ml of standard nitrate (stock) solution into a 100 ml volumetric flask, dilute to the mark with distilled water. Mix well.
Standard Nitrate (working) solution (B), 1 ml = 5 g NO3.
Pipette 10.0 ml of standard nitrate working solution ‘A’ into 100 ml volumetric flasks, dilute to the mark with distilled water. Mix well.
APPARATUS
Water bath
UV/visible range spectrophotometer.
General laboratory glassware.
Calibration procedure
Into a series of 100 ml pyrex beakers, dispense using a micro-burette the volume of standard nitrate working solutions shown in the table below;
Vol. of standard nitrate (working solution in ml) wt NO3 (g) Measure in the following size cell (mm)
SOLUTION (B)
0.00 0 (Blank) 40
1.00 5 40
2.00 10 40
5.00 25 40
10.00 50 40
SOLUTION (A)
2.00 100 10
4.00 200 10
6.00 300 10
8.00 400 10
Continue as under procedure 6.2 to 6.7
For each size cell, construct a calibration graph relating absorbance to weight of nitrate.
PROCEDURE
Pipette 5.00 ml of sample into 100 ml pyrex beaker. If more than 80 mg/l nitrate is expected, pipette a smaller aliquot or dilute sample accordingly. Note sample volume (v) used and dilution (d).
Add using a pipette, 2.0 ml of sodium salicylate solution (0.5% w/v). Mix well and evaporate to dryness on a water bath.
Remove from water bath and add using a pipette and safety pipette filler 1.0 ml of concentrated sulphuric acid. Mix well and allow to stand for 10 minutes.
Dilute to approximately 50 ml with distilled water.
Add using a measuring cylinder 10 ml of sodium hydroxide solution (25 % w/v). Mix thoroughly.
When cool, quantitatively transfer the solution to a 100 ml volumetric flask and dilute to the mark with distilled water. Stopper and mix well.
Measure the absorbance on a spectrophotometer against the blank (100 % transmission) in either a 10 mm cell or 40 mm cell at a wavelength of 410 nm: note the reading
If it is thought that a significant error may be introduced by color or turbidity in the sample, a duplicate sample should be treated exactly as under 6.1 to 6.7 but omitting the addition of the sodium salicylate solution, Step 6.2. Subtract the absorbance of this solution from that obtained for the sample to which salicylate solution has been added.
CALCULATION
Select the calibration graph for the size of cell used and read- off the weight of nitrate present in the solution.
Nitrate content
g NO3 * d/ v mg/l
Where v = sample volume (ml) used and
d = dilution where appropriate.
For nitrate concentrations up to 10 mg/l, report to nearest 0.1 mg/l, above 10 mg/l, report to nearest mg/l.
Thursday, October 4, 2007
Determination of dissolved oxygen in waters and waste water
Hope you guys enjoyed the holidays, di kae dijo tsa boipuso?
OK lets kick start for next weeks lab.
Introduction
Dissolved oxygen (DO) levels in natural and waste waters depend on the physical, chemical and biological activities in the water body and its determination is a key test in water pollution and wastewater treatment process control. Before selecting a method for the determination of DO in water samples, the effect of interference, especially oxidizing and reducing materials that may be present in the sample are considered. Certain oxidizing agents liberate iodine from iodides (positive interference) and some reducing agents reduce iodine to iodide (negative interference). Most organic matter is oxidized partially when the oxidized manganese precipitate is acidified, thus causing negative errors.
There are basically two methods of DO determination; the Winkler or iodometric method and the electrometric method, which uses electrodes. The iodometric method is a titration procedure based on the oxidizing property of DO while the membrane electrode procedure is based on the rate of diffusion of molecular oxygen across a membrane. The choice of procedure depends on the interference present, the accuracy desired and in some cases convenience and experience. Several modifications have been made on the iodometric method to minimize the effect of interference, among which is the Azide modification, the permanganate modification, the alum flocculation modification and the cupper sullfate-sulframic acid flocculation modification. The Azide modification of the Winkler technique will be employed in this practical. This method is appropriate for most wastewater and effluents, (which constitute our samples) and is the most precise and reliable titrimetric procedure for DO analyses. It effectively removes interferences caused by nitrite, which is the most common interference in biologically treated effluents and incubated BOD samples.
Apparatus
General laboratory glassware
DO bottles
Titration set up
Reagents
a. Manganous sulphate solution: Dissolve 480g MnSO4.4H2O, 400g MnSO4.2H2O, or 364g. MnSO4.H2O in distilled water, filter if dissolution is incomplete, and dilute to 1L. The MnSO4 solution should not give a color with starch when added to an acidified potassium iodide (KI) solution.
b. Alkali-iodide-azide reagent: Dissolve 500g NaOH (or 700g KOH) and 135g NaI (or 150g KI) in distilled water and dilute to 1L. Add 10g NaN3 dissolved in 40ml distilled water. This reagent should not give a colour with starch solution when diluted and acidified.
c. Sulphuric acid H2SO4 conc:
d. Starch: Use either an aqueous solution or soluble starch powder mixture: To prepare an aqueous solution, dissolve 2g laboratory grade soluble starch and 0.2g salicylic acid as a preservative in 100 ml hot distilled water
e. Standard sodium thiosulfate titrant (Na2S2O3): Dissolve 6.205g Na2S2O3.5H2O in distilled water. Add 1.5ml 6N NaOH or 0.4 g solid NaOH and dilute to 1000ml. Standardize with bi-iodate solution.
f. Standard bi-iodate solution, 0.0021M: dissolve 812.4mg KH (IO3)2 in distilled water and dilute to 1000ml
g. Potassium fluoride solution: dissolve 40g KF.2H2O in distilled water and dilute to 100 ml.
Procedure
Standardization: Dissolve approximately 2g KI free from iodate in 100 - 150 ml distilled water in an Erlenmeyer flask. Add 1 ml 6N H2SO4 or a few drops of conc H2SO4 and 20ml standard bi-iodate solution. Dilute to 200ml and titrate liberated iodine with thiosulfate titrant, adding a few drops of starch towards the end of titration, when a pale straw color is reached. Titrate to the first disappearance of the blue color.
1. Rinse a 300 ml BOD bottle with sample and pour the sample into the BOD.
2. Add 1 ml MnSO4 solution followed by 1 ml alkali-iodide azide reagent. If pipes are dipped into sample, rinse them before returning them to reagent bottles. Alternatively, hold pipette tips just above liquid surface when adding reagents.
3. Stopper carefully to exclude air bubbles and mix by inverting bottle a few times
4. When precipitate has settled sufficiently (to approximately half the volume of the bottle) to leave a clear supernatant above the manganese hydroxide floc, add 1.0 ml conc H2SO4
5. Re stopper and mix by inverting several times until dissolution is complete.
6. Titrate a volume corresponding to 200 ml original sample after correction for sample loss by displacement with reagent (for a total of 2 ml i.e. 1ml MnSO4 and 1 ml alkali-iodide-azide reagents in a 300 ml bottle, titrate 200 x 300/300-2) = 201ml.
7. Titrate with 0.025M Na2S2O3 solution to a pale straw color.
8. Add a few drops of starch solution and continue titration to first disappearance of blue color.
Calculation
For titration of 200 ml sample, 1 ml 0.025M Na2S2O3 should be equal to 1mg DO/l.
If the molarity of the titrant solution is not 0.025M the calculate DO as follows
DO = Vol of Na2S2O3 used x N/0.025
NB: you can also read more online.
Thank you, see you on Monday
OK lets kick start for next weeks lab.
Introduction
Dissolved oxygen (DO) levels in natural and waste waters depend on the physical, chemical and biological activities in the water body and its determination is a key test in water pollution and wastewater treatment process control. Before selecting a method for the determination of DO in water samples, the effect of interference, especially oxidizing and reducing materials that may be present in the sample are considered. Certain oxidizing agents liberate iodine from iodides (positive interference) and some reducing agents reduce iodine to iodide (negative interference). Most organic matter is oxidized partially when the oxidized manganese precipitate is acidified, thus causing negative errors.
There are basically two methods of DO determination; the Winkler or iodometric method and the electrometric method, which uses electrodes. The iodometric method is a titration procedure based on the oxidizing property of DO while the membrane electrode procedure is based on the rate of diffusion of molecular oxygen across a membrane. The choice of procedure depends on the interference present, the accuracy desired and in some cases convenience and experience. Several modifications have been made on the iodometric method to minimize the effect of interference, among which is the Azide modification, the permanganate modification, the alum flocculation modification and the cupper sullfate-sulframic acid flocculation modification. The Azide modification of the Winkler technique will be employed in this practical. This method is appropriate for most wastewater and effluents, (which constitute our samples) and is the most precise and reliable titrimetric procedure for DO analyses. It effectively removes interferences caused by nitrite, which is the most common interference in biologically treated effluents and incubated BOD samples.
Apparatus
General laboratory glassware
DO bottles
Titration set up
Reagents
a. Manganous sulphate solution: Dissolve 480g MnSO4.4H2O, 400g MnSO4.2H2O, or 364g. MnSO4.H2O in distilled water, filter if dissolution is incomplete, and dilute to 1L. The MnSO4 solution should not give a color with starch when added to an acidified potassium iodide (KI) solution.
b. Alkali-iodide-azide reagent: Dissolve 500g NaOH (or 700g KOH) and 135g NaI (or 150g KI) in distilled water and dilute to 1L. Add 10g NaN3 dissolved in 40ml distilled water. This reagent should not give a colour with starch solution when diluted and acidified.
c. Sulphuric acid H2SO4 conc:
d. Starch: Use either an aqueous solution or soluble starch powder mixture: To prepare an aqueous solution, dissolve 2g laboratory grade soluble starch and 0.2g salicylic acid as a preservative in 100 ml hot distilled water
e. Standard sodium thiosulfate titrant (Na2S2O3): Dissolve 6.205g Na2S2O3.5H2O in distilled water. Add 1.5ml 6N NaOH or 0.4 g solid NaOH and dilute to 1000ml. Standardize with bi-iodate solution.
f. Standard bi-iodate solution, 0.0021M: dissolve 812.4mg KH (IO3)2 in distilled water and dilute to 1000ml
g. Potassium fluoride solution: dissolve 40g KF.2H2O in distilled water and dilute to 100 ml.
Procedure
Standardization: Dissolve approximately 2g KI free from iodate in 100 - 150 ml distilled water in an Erlenmeyer flask. Add 1 ml 6N H2SO4 or a few drops of conc H2SO4 and 20ml standard bi-iodate solution. Dilute to 200ml and titrate liberated iodine with thiosulfate titrant, adding a few drops of starch towards the end of titration, when a pale straw color is reached. Titrate to the first disappearance of the blue color.
1. Rinse a 300 ml BOD bottle with sample and pour the sample into the BOD.
2. Add 1 ml MnSO4 solution followed by 1 ml alkali-iodide azide reagent. If pipes are dipped into sample, rinse them before returning them to reagent bottles. Alternatively, hold pipette tips just above liquid surface when adding reagents.
3. Stopper carefully to exclude air bubbles and mix by inverting bottle a few times
4. When precipitate has settled sufficiently (to approximately half the volume of the bottle) to leave a clear supernatant above the manganese hydroxide floc, add 1.0 ml conc H2SO4
5. Re stopper and mix by inverting several times until dissolution is complete.
6. Titrate a volume corresponding to 200 ml original sample after correction for sample loss by displacement with reagent (for a total of 2 ml i.e. 1ml MnSO4 and 1 ml alkali-iodide-azide reagents in a 300 ml bottle, titrate 200 x 300/300-2) = 201ml.
7. Titrate with 0.025M Na2S2O3 solution to a pale straw color.
8. Add a few drops of starch solution and continue titration to first disappearance of blue color.
Calculation
For titration of 200 ml sample, 1 ml 0.025M Na2S2O3 should be equal to 1mg DO/l.
If the molarity of the titrant solution is not 0.025M the calculate DO as follows
DO = Vol of Na2S2O3 used x N/0.025
NB: you can also read more online.
Thank you, see you on Monday
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