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Environmental Engineering Laboratory Manual for Water and Waste Water Analysis.Prepared by Mr. Santosh Kumar Kharole for bachelor of Civil Engineering Students of University Institute of Technology, Rajiv Gandhi Proudyogiki Vishwavidyalaya , Bhopal.
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EXPERIMENT No . 3
ALKALINITY
OBJECT
To determinate alkalinity of given sample of water.
APPARATUS
Burette, Pipette, Conical flask and Glazed tile.
REAGENTS
0.02 N H2SO4 solution, Phenolphthalein indicator and Methyl orange indicator.
THEORY
Alkalinity is the measure of the basic constituents of water and is defined the
capacity of a solution to neutralize a standard acid. In natural water it is usually present as
the carbonate and bicarbonate salts of calcium, magnesium, sodium and potassium.
Bicarbonates represent the major form of alkalinity since they are formed in
considerable amounts from the action of carbon dioxide upon basic materials in the soil.
Under certain conditions natural water may contain appreciable amount of carbon and
hydroxide alkalinity. Chemically treated water, particularly those produced in lime or
lime soda ash softening of water, contain carbonates and excess hydroxide.
Thus it is obvious that alkalinity is caused by three major classes of materials may
be ranked in order of their effect on pH as hydroxides, carbonates, bicarbonates and other
salts of weak acids.
Alkalinity is determined by titration with a standard with a standard solution of a
strong acid to certain end points as given by indicator solutions. Phenolphthalein is
satisfactory indicator for the first end point (pH approx 8.3) contributed by hydroxide and
carbonate. Methyl orange is used for the second end point (pH approx 4.5) contributed by
bicarbonates. The phenolphthalein end point of titration is defined as ‘P’ alkalinity and
the end point observed by continuing the titration with same solution using methyl orange
indicator is known as total or T-alkalinity. Following table can be used for working out
OH, CO3 and HCO3 alkalinity individually after completing titration.
Table
Result of Titration Value of radical expressed in term of Calcium Carbonate
OH- CO3-- HCO3-P = 0P < (T/2)P = (T/2)P > (T/2)P = T
000
2P-TT
02P2P
2(T-P)0
TT-2P
000
PROCEDURE
Phenolphthalein alkalinity
The 50 or 100 ml of sample in an Erlenmeyer flask, add two drops of phenolphthalein indicator and titrate over a white tile with 0.02 N H2SO4 until the pink colour just disappears.
Total or methyl orange alkalinity
Add two drops of methyl orange indicator to the same sample in which phenolphthalein alkalinity has been determine previously and titrate with 0.02 N H2SO4 until the colour changes from yellow to faint orange.
OBSERVATIONS
(a) Sample .……………
(b) Initial pH of given sample is …………….
Table for phenolphthalein alkalinity
S.No. Volume of Sample Initial burette reading
Final burette Reading
Volume of H2SO4
1.2.3.
Table for methyl orange alkalinity
S.No.Volume of sample Initial burette
readingFinal burette
readingVolume of
H2SO4
1.2.3.
CALCULATIONS
Initial pH of the sample is………………………………..
Mg/lt. phenolphthalein alkalinity as CaCO3 = …………………
(ml. of 0.02N H2SO4 x 10 0 0 x 5 0) = ………………..ml. of sample
Mg/lt. of total or methyl orange alkalinity as CaCO3 =
Total ml. of 0.02 N H2SO4 x 1000 x 50 =…………………ml. of sample.
RESULT
Methyl orange alkalinity as CaCO3 is ……............mg/lt. and Phenolphthalein alkalinity
is ……….. mg/lt.
Total alkalinity due to bicarbonate is got by using methyl orange indicator it comes
………..…. mg/lt.
CONCLUSION
Since alkalinity of tap water …… mg/lt. which is very large/moderate/low. Thus it can be
used/not used as drinking water because according to IS-10500:1991 range of alkalinity
for drinking water is 200-600 mg/lt. OH- ion is mainly responsible for alkalinity. Due to
only OH- ion alkalinity has range of pH 8.3 to 14 and practical range of alkalinity comes
pink to colorless solution of alkalinity above 600 mg/lt. is not good for human point of
view.
SIGNIFICANCE
With in regional limit alkalinity has sanitary significance, but it is very important in
connection with coagulation, softening and corrosion preservation, Alum used in
coagulation is an acid salt which when added in small quantity to natural water, reacts
with alkalinity present to form flocs. If insufficient alkalinity is present to react with all
the alum, coagulation will be incomplete and soluble alum will be left in the water. It
may therefore, be necessary to add alkalinity in the form of soda ash or lime to complete
the coagulation or to maintain sufficient alkalinity to prevent the coagulated water fro
being corrosive. Ordinarily the total alkalinity determined with methyl orange indicator;
gives sufficient information for the control of coagulation and corrosion prevention when
pH is also determined.
Many regulatory agencies prohibit the discharge of waste containing caustic alkalinity to
receiving water. Municipal authorities usually prohibit discharge of waste containing
caustic alkalinity to sewers. Alkalinity as well as pH is an important factor in determining
the amenability of waste water to biological treatment.
Lastly from public health point of view, alkaline water is usually unpalatable and
consumer tends to seek other supplies Chemically treated water some time have rather
pH values, which have met with some objections on the part of consumers. For these
reasons, standards are some times established on chemically treated water.
Where biological processes of treatment are used the pH must ordinarily be maintained
within the range of 6 to 9.5. This criterion often requires adjustment of pH to favorable
levels and calculations of the amount of chemical needed is based upon acidity values in
most cases.
EXPERIMENT No. 4
CHLORIDE TEST
OBJECT
To determine the amount of chlorides in the given sample.
APPARATUS
Burette, Pipette and Conical flask, Silver nitrate (N/71), Potassium chromate indicator,
chemicals for pH adjustments.
THEORY
Chlorides occur in all natural water in widely varying concentrations. This chloride
content normally increases as the mineral content increases and it is usually associated
with Na + ion. The sources which contribute most of the increase of chlorides in natural
water are:
(i) Due to the formation of minute salt crystals resulting from evaporation of ocean
water and then its spraying over inland areas.
(ii) Due to the solvent power of water which dissolves chlorides from top soil and
deeper formations.
(iii) Due to sea water intermixing with river water and due to over pumping that
causes sea water intrusion in group water.
(iv) Due to discharge of sewage effluents in surface water as the chloride content of
urine are about 6gms. per person per day.
(v) Due to discharge of industrial wastes in surface sources or due to seepage in
ground water.
PROCEDURE
(i) Clean the burette, pipette and conical flask with the tap water.
Adjust the pH of sample between 7.0 and 8.0.
(ii) Take 50 ml well mixed sample adjusted to pH 7.0 -8.0 and add 1.0 ml K2CrO4.
Note initial burette reading.
(iii) Titrate with standards AgNO3 solution till Ag2CrO4 starts precipitating giving
red color.
(iv) Note final burette reading.
(v) Repeat the procedure till the concurrent readings are obtained.
(vi) Determine the blank reading with the same procedure using distilled water.
OBSERVATIONS
The initial pH of the sample is ………………..
S. No. Volume of sample Volume of AgNO3 ( ml ) Net volume of AgNO3 (ml)
Initial reading Final reading A. Tap water
1.
2.
3.
B. Distilled water
1.
2.
3.
SAMPLE CALCULATIONS
Initial pH is …………………for tap water.
Mg/lt. = (A-B) x 0.5 x 1000 =………………………ml. of sample
Where AgNO3 for sample is = ……………………
Where AgNO3 for Blank is = …………………….
Where A = ml. of AgNO3 for sample, B = ml of AgNO3 for blank
RESULT
The chloride content of given sample is found to be ………………mg/lt. as Cl.
CONCLUSION
In a given sample ……..…mg/lt chlorides present, which is Harmful / not harmful. In
first AgNo3 react with salt which has chlorides and make white precipitate and AgCl then
(indicator K2CrO4) react with AgNO3 and given brick red color. Thus at last end point
comes brick red precipitate.
SIGNIFICANCE
Chlorides are not harmful as such but when it exceed beyond 250 mg/l it imparts a
peculiar taste to water rendering it unacceptable from aesthetic point of view for drinking
purpose. Presence of chlorides above the usual background concentration water source is
also used as an indicator for pollution by domestic sewage.
Before the development of bacteriological testing procedures, chemical tests for chloride
and for nitrogen, in its various forms, served as the basis of detecting contamination of
ground water by sewage. Chlorides are used to some extent as tracers in sanitary
engineering practices.
Where brackish water has to be used for domestic purposes, the amount of chlorides
present in the source is an important factor in determining the type of desalting apparatus
to be used. The chloride determination is used to control pumping of ground water from
locations where intrusion of sea water is a problem.
EXPERIMENT No. 5
HARDNESS TEST
OBJECT
To determine the total hardness and calcium hardness of a given sample of water.
APPARATUS
Burette, Pipette, Conical flask, etc.
REAGENTS
Standard EDTA solution (N/50), Ammonia buffer solution and NaOH solution, Eriochrome black T indicator and Murex indicator (dry power), inhibitor.
THEORY
Water that consumes considerable quantity of soap to produce lather and or produces
scale in hot-water pipes, heater, boilers and utensils used for cooking is called hard water.
Harness is caused by divalent metallic anions that are capable of reacting with soap to form precipitates with cations present in water to form scale. Principal actions causing hardness and the major anions associated with them are as listed below:
CATIONS ANIONS
Ca++ HCO3-Mg++ SO4--Sr++ Cl-Fe++ NO3-Mn++ SiO3--
Calcium and magnesium are primarily the constituents of chalk and limestone. When rain
falls it takes up carbon dioxide from the atmosphere and forms a weak acid and this
percolates underground, it then dissolves calcium and magnesium forming hard water.
IN general hard water originates in the areas where the topsoil is thick and limestone
formations are present. Soft water originates in areas where the topsoil is thin and
limestone is either sparse or absent.
0 50100150Over
50 ppm100ppm150ppm250 ppm 250 ppm
Soft Moderately soft Slightly hard Moderately hard Hard
The scale of hardness from consumer’s point of view may be taken as below:
Hardness may be classified as:
(a) Carbonate and non carbonate hardness
(b) Calcium and magnesium hardness, and
(c) Temporary and permanent hardness.
PRINCIPLE
In alkaline condition EDTA (Ethylene-diamine tetra acetic acid) or its sodium salt forms
a soluble chelated complex, which is stable with Ca and Mg. Also Ca and Mg form a
weak complex with the indicator Eriochrome black T, which has wine red color. During
titration when all free hardness ions are complexed by Eriochrom black T indicator end
point. The pH has to maintain at 10+0.1.
At higher pH i.e. about 12.0 mg ion precipitates and only Ca++ ions remain in solution.
At this pH murex indicator from a pink colour with Ca++, gets complexed resulting in a
change from pink to purple, which indicates and point of the reaction.
INTERFERENCE
Metal ions do interfere but can overcome by addition of inhibitors.
PROCEDURE
A. TOTAL HARDNESS
1. Rinse burette, pipette, and flask, etc.
2. Take 25 or 50 ml of well-mixed sample in a flask.
3. Add 1-2 ml buffer solution followed by 1 ml inhibitor.
4. Add a pinch of Eriochrome black T and titrate with standard EDTA solution till
wine red colour changes to blue. Note down the volume of EDTA required.
B. CALCIUM HARDNESS
1. Take 25 ml of sample in a flask.
2. Add 2-3 drops of NaOH (N/10) to raise pH to 12 and a pinch of indicator. Note
initial burette readings.
3. Titrate with EDTA till pink colour changes to purple . Note the final burette
readings.
4. Repeat the procedure for other sample s till concurrent readings are obtained.
C. MAGNESIUM HARDNESS 1. Take 100 ml of sample , add 1.5 ml of the buffer solution and 2.3 ml of a
saturated solution of ammonia oxalate.
2. Mix the solution and allow it to stand for two hours or overnight if possible.
3. Filter , using a No. 42 Watman filter paper.
4. Pipette out 25 ml from the filtered solution and add Eriochrome black tT
indicator (1-2 drops) and titrate with EDTA solution till the colour changes from
wine red to blue.
5. Take two concurrent readings.
OBSERVATIONS FOR TOTAL HARDNESS
S.No. Volume of sample Initial reading
Final reading
Net volume of EDTA
(ml)
Total hardness mg/lt. as CaCO3
1.2.3.
4.
OBSERVATIONS FOR CALCIUM HARNDNESS
S.No. Volume of sample Initial reading
Final reading
Net volume of EDTA
(ml)
Calcium hardness
mg/lt. 1.2.3. 4.
SAMPLE CALCULATIONS
(a) Total harndness: Total hardness (mg/litre) = ml. of EDTA x 1 x 1000 ml. of sample (b) Calcium harndness :
Calcium hardness (mg/litre) = ml. of EDTA x 1 x 1000 ml. of sample (c) Magnesium harndness: Magnesium hardness (mg/litre) = Total hardness - Ca
RESULT For the given tap water sample the hardness is found to be ……… mg/lt., Calcium hardness is ……. mg/lt. and Magnesium hardness is ……… mg/lt.
CONCLUSION
As the total hardness and calcium hardness are below/above the maximum tolerable value i.e. 600 and 200 respectively. The water can be used/not used for domestic purposes.
SIGNIFICANCE
The determination of hardness is helpful in deciding the suitability of water for domestic and industrial purpose. The design of softening process depends upon the relative amounts of carbonate and non-carbonate hardness present in water. The amount of calcium and magnesium hardness decides the suitability of water for boiler use.