OBJECTIVE
To determine the Biochemical Oxygen Demand of the given water samples.
PRINCIPLE
The iodometric titration is precise & reliable titrimetric procedure for dissolved oxygen (DO) analysis. The test is based on the addition of divalent manganese solution; followed by strong alkali, to the sample in a BOD glass stoppered bottle. DO present, rapidly oxidize an equivalent amount of the dispersed divalent manganous hydroxide of higher oxidation state (brownish orange in colour). This brownish orange colour indicates presence of oxygen. In the presence of iodide and on subsequent acidification, higher manganese hydroxide revert to the divalent state, & liberate iodine equivalent to the original DO content of the sample. The iodine liberated is titrated with a standard solution of sodium thiosulphate using starch as indicator.
REACTIONS INVOLVED
MnSO4 + 2 KOH Mn(OH) 2 + K2 SO4
(white ppt.)
2Mn(OH) 2 + O2 2MnO(OH) 2
(brown ppt.)
MnO(OH) 2 + 2H2SO4 Mn(SO4) 2 + 3 H2 O
Mn(SO4) 2 + 2KI MnSO4 + K2SO4 + I2
2Na2 S2 O3 .5 H2 O + I2 Na2 S4 O6 + 2 Na I + 10 H2 O
2NaN3 + H2SO4 2HN3 + 2Na2 SO4
HNO2 + HN3 N2 + N2O + H2 O
INTERFERENCE
It is caused by certain oxidizing agents which liberate iodine from iodides (such as ozone, chlorine, ferric compounds, higher oxidation state chromate, nitrate, persulphate, peroxides, etc), by certain reducing agents which may reduce iodine to iodide (such as ferrous compounds, thiosulphate, readily oxidizable organic matter, nitrite, etc). some organic compound hinder the setting of precipitate and colour of starch end point.
PROCEDURE
1) Fill the BOD bottle without turbulently exposing the sample to the air, & stopper it.
2) Add 2ml manganous sulphate followed by 2ml alkali-iodide-azide reagent, dipping the pipette little below the surface
3) Stopper carefully to exclude the air bubbles, & thoroughly mix the contents by inverting the bottle.
4) Allow the precipitate to settle to the 1/3rd of the bottle, repeat the mixing & allow the precipitate to settle completely leaving a clear supernatant liquid.
5) Add 2ml conc H2SO4 immediately after removing the stopper. Restopper and mix by gentle inversion until all the precipitate dissolve, if it doesn’t, allow to stand for a few minutes and repeat the mixing.
6) Distribute the iodine uniformly before taking a part of it for titration.
7) Pipette 100ml of sample for titration in 250ml conical flask and immediately titrate the liberated iodine with the standard sodium thiosulphate solution to a pale yellow straw colour. Add 2ml starch solution and continue the titration till the first disappearance of the blue colour.
8) Repeat the steps (2-7) for the bottles incubated at 27°C for 3 days to get the dissolved oxygen on the finale day.
NOTE: It must be remembered that iodine is volatile and therefore, the titration must be carried out as expediously as possible and with the minimum exposure to the air.
FORMULA USED
BOD (mg/l) = {(IDDOS- FDDOS) – (IDDOB-FDDOB)X100}/ Percent Of Solution .
Where, IDDOS- Initial day dissolved oxygen Sample
FDDOS- Finale Day Dissolved Oxygen Sample
IDDOB- Initial Day Dissolved Oxygen Blank
FDDOB-Finale Day Dissolved Oxygen Blank
OBSERVATIONS
The BOD of the groundwater samples is negligible, hence it is not determined. The BOD values of the polluted river stretch is only determined.
Total Observations= 6 (blank) + 3 x 2 (bottles per sample x no. of samples)
= 12
2 blanks are for initial day DO and 4 for final day DO.
1 sample bottle is for initial day DO and 2 for final day DO.
% Dilution = 10 %
S.No. Bottle No. Sample Description Volume (ml)
1. 4 Blank: Initial Day 6.10
2. 8 Blank: Initial Day 6.15
3. 22 Blank: Final Day 6.24
4. 45 Blank: Final Day 6.45
5. 60 Blank: Final Day 6.04
6. 70 Blank: Final Day 6.00
13. 198 Sample 3: Initial Day 4.92
14. 202 Sample 3: Final Day 2.19
15. 207 Sample 3: Final Day 1.96
16. 370 Sample 4: Initial Day 5.05
17. 465 Sample 4: Final Day 2.23
18.. 785 Sample 4: Final Day 2.81
RESULTS
Sample No. BOD (mg/l)
3. 29.025
4. 25.875
By-Riddhi singh
Wednesday, August 20, 2008
OBJECTIVE
To determine the Total Dissolve Solids in the given water samples.
PRINCIPLE
Basic principle involved is gravimetric. A well mixed sample is filtered through standard glass fibre filter and the filtrate is evaporated to dryness in an oven at 103 - 105◦C. The increase in weight represents the TDS.
The term residue denotes the material remaining in the dish after evaporation of water sample and drying in an oven at a definite temperature.
INTERFERENCE:
Highly mineralized water with considerable calcium, magnesium, chloride and/or sulphate content may be hygroscopic and require prolonged drying, proper dessication and rapid weighing.
PROCEDURE:
1) Dry the well cleaned dish in an oven at 103 – 105 ◦C for 1 hr
2) Cool, dessicate and take the initial weight of the dish
3) Repeat the above test (2) until a constant weight is obtained
4) Transfer a known volume of filtered homogenous sample into the dish.
5) Evaporate to dryness on a steam bath
6) Dry the evaporated sample in an oven at 103 – 105 ◦C for 1hr
7) Cool in dessicator and weigh
FORMULA USED
TDS (mg/ltr) = {(A-B) x 10^6}/V
Where, A = weight of dish residue in mg
B = weight of dish in mg
V = volume of sample in ml
OBSERVATIONS
V= 25 ml
Sample No. A B
1. 47.7494 47.7165
2. 48.6725 43.9419
3. 44.8594 44.8357
4. 52.7158 52.6922
RESULTS
Sample No. TDS (mg/l)
1. 1316
2. 1324
3. 948
4. 944
The results show that the TDS in groundwater samples is greater than that of the polluted samples.
By-Riddhi singh
To determine the Total Dissolve Solids in the given water samples.
PRINCIPLE
Basic principle involved is gravimetric. A well mixed sample is filtered through standard glass fibre filter and the filtrate is evaporated to dryness in an oven at 103 - 105◦C. The increase in weight represents the TDS.
The term residue denotes the material remaining in the dish after evaporation of water sample and drying in an oven at a definite temperature.
INTERFERENCE:
Highly mineralized water with considerable calcium, magnesium, chloride and/or sulphate content may be hygroscopic and require prolonged drying, proper dessication and rapid weighing.
PROCEDURE:
1) Dry the well cleaned dish in an oven at 103 – 105 ◦C for 1 hr
2) Cool, dessicate and take the initial weight of the dish
3) Repeat the above test (2) until a constant weight is obtained
4) Transfer a known volume of filtered homogenous sample into the dish.
5) Evaporate to dryness on a steam bath
6) Dry the evaporated sample in an oven at 103 – 105 ◦C for 1hr
7) Cool in dessicator and weigh
FORMULA USED
TDS (mg/ltr) = {(A-B) x 10^6}/V
Where, A = weight of dish residue in mg
B = weight of dish in mg
V = volume of sample in ml
OBSERVATIONS
V= 25 ml
Sample No. A B
1. 47.7494 47.7165
2. 48.6725 43.9419
3. 44.8594 44.8357
4. 52.7158 52.6922
RESULTS
Sample No. TDS (mg/l)
1. 1316
2. 1324
3. 948
4. 944
The results show that the TDS in groundwater samples is greater than that of the polluted samples.
By-Riddhi singh
Conductivity of water sample
OBJECTIVE
To determine the conductivity of the given water samples.
PRINCIPLE
Conductivity meter is standardized with standard KCl to adjust the internal cell constant of the instrument, matching the conductivity of KCl solution. Alter standardization (.i.e. setting cell constant) measure conductivity of the unknown solution.
Conductivity is a measure of the ability of an aqueous solution to carry an electric current, which depends on the ionic strength of the water.
APPARATUS
Conductivity meter: If an aqueous solution conducts electricity, then it must contain ions. So measuring the conductance of solutions can tell you whether the solutes in the solution are dissociated into ions, and whether chemical reactions in solution are producing or consuming ions.Any solution, even one containing ions, provides considerable resistance to the flow of current through it. Conductivity is, roughly speaking, the reciprocal of this resistance -- high resistance means low conductivity; low resistance means high conductivity.
PROCEDURE
1) Warm the instrument for 15 – 20 minutes
2) Bring the standard KCl solution and the sample to 25°C
3) Rinse the electrode with standard KCl solution
4) Rinse the electrode with distilled water and the sample
5) Measure the conductivity directly, when it becomes stable
RESULTS
Sample No. Conductivity
1. 500 µS
2. 480 µS
3. 1360 µS
4. 1380 µS
The results clearly indicate the excessive concentration of ionic matter in the polluted river sample.
By-Riddhi singh
To determine the conductivity of the given water samples.
PRINCIPLE
Conductivity meter is standardized with standard KCl to adjust the internal cell constant of the instrument, matching the conductivity of KCl solution. Alter standardization (.i.e. setting cell constant) measure conductivity of the unknown solution.
Conductivity is a measure of the ability of an aqueous solution to carry an electric current, which depends on the ionic strength of the water.
APPARATUS
Conductivity meter: If an aqueous solution conducts electricity, then it must contain ions. So measuring the conductance of solutions can tell you whether the solutes in the solution are dissociated into ions, and whether chemical reactions in solution are producing or consuming ions.Any solution, even one containing ions, provides considerable resistance to the flow of current through it. Conductivity is, roughly speaking, the reciprocal of this resistance -- high resistance means low conductivity; low resistance means high conductivity.
PROCEDURE
1) Warm the instrument for 15 – 20 minutes
2) Bring the standard KCl solution and the sample to 25°C
3) Rinse the electrode with standard KCl solution
4) Rinse the electrode with distilled water and the sample
5) Measure the conductivity directly, when it becomes stable
RESULTS
Sample No. Conductivity
1. 500 µS
2. 480 µS
3. 1360 µS
4. 1380 µS
The results clearly indicate the excessive concentration of ionic matter in the polluted river sample.
By-Riddhi singh
pH of water
OBJECTIVE
To determine the pH of the given water sample.
PRINCIPLE
At given temperature the intensity of the acidic or basic character of the sample is indicated by pH or hydrogen ion activity. The activity of H+ ions is determined by pH meter.
INTERFERENCE:
At higher pH values, the members become somewhat sensitive to sodium and other alkali ions. Also temperature affects the pH measurement.
APPARATUS
pH meter :A pH meter is an electronic instrument used to measure the pH (acidity or basicity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances, such as cheese). A typical pH meter consists of a special measuring probe (a glass electrode) connected to an electronic meter that measures and displays the pH reading.
PROCEDURE
1) Rinse the electrode with distilled water.
2) Standardize the instrument using buffer solution.
3) Rinse the electrode with distilled water.
4) Immerse the electrode in the sample.
5) Take the reading when it becomes stable.
RESULTS
The following values were observed:
Sample No. pH
1. 7.32
2. 7.19
3. 7.39
4. 7.46
The pH values don’t show any marked departure from normal.
By-Riddhi singh
To determine the pH of the given water sample.
PRINCIPLE
At given temperature the intensity of the acidic or basic character of the sample is indicated by pH or hydrogen ion activity. The activity of H+ ions is determined by pH meter.
INTERFERENCE:
At higher pH values, the members become somewhat sensitive to sodium and other alkali ions. Also temperature affects the pH measurement.
APPARATUS
pH meter :A pH meter is an electronic instrument used to measure the pH (acidity or basicity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances, such as cheese). A typical pH meter consists of a special measuring probe (a glass electrode) connected to an electronic meter that measures and displays the pH reading.
PROCEDURE
1) Rinse the electrode with distilled water.
2) Standardize the instrument using buffer solution.
3) Rinse the electrode with distilled water.
4) Immerse the electrode in the sample.
5) Take the reading when it becomes stable.
RESULTS
The following values were observed:
Sample No. pH
1. 7.32
2. 7.19
3. 7.39
4. 7.46
The pH values don’t show any marked departure from normal.
By-Riddhi singh
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