INDEX

ENVIRONMENTAL ENGINEERING LAB

1. Determining the concentration of sodium and potassium in water sample using flame photometer
2. Determination of optimal coagulant dosage using jar test
3. Determination of turbidity in water sample using nephelo turbidity meter
4. Determination of alkalinity
5. Determination of residual chlorine
6. Estimation of chloride
7. Determination of Dissolved Oxygen (D.O)
8. Estimation of total hardness and calcium hardness in water sample
9. Determination of Total Solids
10. Determination of B.O.D.
11. Determination of C.O.D
    

Questions for viva voce

Answers

Questions suggested for viva voce

QUESTIONS & ANSWERS

1. What is hardness of water 
2. What is temporary hardness and how can it be removed
3. What is permanent hardness and how can it be removed
4. What is meant by dissolved oxygen
5. What is the maximum value for dissolved oxygen in water
6. What is B.O.D (Biochemical Oxygen Demand)
7. What is C.O.D (Chemical Oxygen Demand)
8. What is alkalinity
9. Define turbidity
10. What is meant by residual chlorine
11. What is the significance of jar test
12. What is sedimentation
13. What is coagulation
14. What is flocculation
15. What are the ill-effects of hard water
16. What is BOD ?
17. What is the difference between BOD and DO(Dissolved Oxygen). If BOD is high (~300 ppm), what is the value of DO (low or high)
18. What is the difference between BOD and COD. Which is higher and why
19. What is the significance of turbidity in water treatment
20. Name the method used to determine DO
21. What is a coagulant and why is it used
22. What is residual chlorine and what is its permissible value
23. What is the permissible limit of chloride content in water
24. What is break-point chlorination
25. Why is a graph plotted to determine the optimum dosage of coagulant
26. What is the source for chlorides in water
27. What is the minimum DO content to support aquatic life
28. What is the saturation value for DO
29. Define alkalinity and its significance in water treatment
30. What is standardisation of titrant
31. Define Normality
32. What is dilution ratio and where is it used
33. What is Hypochlorous acid and what is its application
34. In the Starch-Iodide method for determination of residual chlorine, why is the flask kept in a dark place for five minutes during the standardisation of sodium thio sulphate using potassium dichromate
35. What is meant by standardisation of a reagent and why is it done
36. How are alkalinity and hardness related
37. How are hardness and alkalinity expressed
38. Expand EDTA and EB-T
39. What is 'Winkler's Test' conducted for and what is it also known as
40. What is the saturation value for DO
41. What is the permissible limit for chloride content in water
42. What are the types of alkalinities
43. What are ions contributing to alkalinity in water
44. What are the units of turbidity
45. What is meant by a 'stock solution' and what are the chemicals used to prepare stock turbidity solutions 
46. Explain how the turbidity of a solution is calculated if the meter reading is beyond the range calibrated
47. What is alum and where is it used in water treatment
48. What is the function of a coagulant
49. What happens if too little or too much of a coagulant is added to water
50. In what way are hardness and alkalinity expressed and why

ANSWERS

Determining the concentration of sodium and potassium in water sample using flame photometer

DETERMINING THE CONCENTRATION OF SODIUM AND POTASSIUM IN WATER SAMPLE USING FLAME PHOTOMETER

AIM:-To determine the concentration of sodium and calcium using flame photometer.

APPARATUS:- Flame Photometer.

THEORY:- Sodium, potassium and calcium are abundantly available in nature and their salts are highly soluble in water. Hence most of the water samples contain these elements in varying quantities depending upon the source of water. Even though, they are harmless in small quantities, excessive concentrations may impart a bitter taste to water and may make the water hazardous  to the health of cardial and kidney patients. Sodium is corrosive to metals surface and in large concentrations it is toxic to plants.

            The principle of working of flame photometer is very simple. The sample is sprayed as fine mist into non-lumbinous flame which becomes coloured depending upon the characteristics of the emissions of the elements present in the sample water. The equipment has two channels which work simultaneously. Each channel has a detective device which views the flame through a narrow band optical filter that only passes the wave lengths centered around the characteristics emissions of the selector element. For sodium, this wave length is 589nm and for potassium it is 768nm. The output of the detector is passes on to an electronic metering device which converts the input to a digital readout

            Concentrations in the range of 0-2m.eq. per lit of sodium and 0-0.1m.eq.per lit of potassium can be measured with the equipment after calibration.

RELAVANCE:- Potassium is a major chemical constituent of potable water. The average level of sodium is greater than 100mg/lit. Higher amounts of sodium render boiler operations difficult. High concentration of sodium in blood leads to hyper tension. Soil permeability can be affected by concentration of sodium. Potassium is generally not found in water in high concentration. The ratio of sodium to potassium is generally 10:1 to 20:1.

CHEMICAL REAGENTS:

i)                    Deionized water

ii)                  Sodium chloride

iii)                Potassium chloride

PROCEDURE:-

a) Calibration of the flame photometer:-

i)                    Prepare 1000ppm Nacl solution by dissolving 2.5416 grams of Nacl salt in 1.0 lit of deionozed water. Using this stock solution, prepare a standard solution of 1.0m.eq.per lit (1.0m.eq./lit=23ppm)

ii)                  Prepare 1000ppm Kcl solution by dissolving 1.907 grams of Kcl salt in 1.0lit of deionized water. Using this stock solution, prepare standard solution of 0.08m.eq.’lit(1.0m.eq/lit=39ppm). These two standard solutions are used for the calibration of equipment.

b) Procedure:-

1. Switch on the power supply and allow the instrument to warm up for about 5 mins.
2. Switch on the air compressor and set the pressure between 0.3-0.6 kg/cm2
3. Light the flame and adjust the gas supply so that a low intensity blue flame is obtained.
4. Set all the coarse and fine controls to the maximum position and select the sodium and potassium filters.
5. Feed deionized water to atomizer and wait atleast for 30 seconds.
6. Adjust the “Set Reference” course and fine controls for zero readout for potassium and sodium.
7. Aspirate 1.0m.eq/lit. of sodium solution and wait at least 30 seconds and then adjust the “set F.S” course and fine controls for a readout of 100 for sodium only.
8. Aspirate 0.08m.eq/lit. of potassium solution and wait atleast 30 seconds and then adjust the “set F.S” coarse and fine control for a readout of 80 for potassium only.
9. Repeat steps 6 to 8 until the readings are stabilized the equipment now stands calibrated.

c) Determination of sodium and potassium concentration in the given sample water:-

Feed the sample to the atomizer and obtain the readings corresponding to sodium and potassium. If the concentrations of sodium and potassium in the sample water is more than the measurable limit of the equipment, the unit will not show a meaningful display. In that case the sample has to be diluted so as to get a meaningful digital read out. Note down the extent of dilution of the sample (i.e. dilution factor). Let 10ml of sample water is diluted to 50ml by adding deionozed water. Let the readings be 62 and 31 for sodium and potassium respectively.

Specimen calculations:

Dilution factor = ml of diluted sample   =  50  =  5

                             ml of sample                   10

Concentration of sodium

in mg/lit                                   =  62*1*23*5 = 71.3 mg/lit

                                                   100

Concentration of potassium

in mg/lit.                                  = 31 *0.08*39*5  = 6.045 mg/lit

                                                    80

OBSERVATIONS:-

Sample No.	Digital readout for		Dilution factor
	Na	K

CALCULATIONS:-

RESULTS:-

INTERPRETATION OF RESULTS:-

Determination of optimal coagulant dosage using jar test

DETERMINATION OF OPTIMUM COAGULANT DOSE USING JAR TEST APPARATUS

AIM:- To determine the optimum coagulant dose.

APPARATUS:- Jar test apparatus and Nephelo turbidity meter.

THEORY:- In plain sedimentation, very fine suspended particles of size 0.006mm to 0.002mm are not removed, since they required a detention period of 10 hours to 4 days which is impracticable. In addition to this fine suspended particle, water also contains electrically charged colloidal particles which are continuously in motion and never settle down due to gravity. It has been found that, the above mentioned impurities can be removed by sedimentation with coagulation.

            It has been found that when certain chemicals (i.e. coagulants) are added to water an insoluble, gelatinous precipitate is formed. This precipitate during its formation and descent through the water absorbs very fine suspended and colloidal impurities there by reducing the turbidity of the water.

RELEVANCE:-

            Coagulation of raw water using the optimum coagulant dose removes colloidal impurities from the water. These colloidal impurities are normally associated with organic matter containing pathogenic bacteria which are responsible for water borne diseases. The chemical coagulation also makes the process of disinfection more effective. Coagulation also removes objectionable colour, taste and odour’s from water. Usually the dose of Alum varies between 5mg/lit for relatively clear water to about 85 mg/lit for very turbid waters. The average dose is about 20mg/lit.

CHEMICAL REAGENTS:-

ALUM SOLUTIONS:- Dissolve 1.0 gram of Alum in 1 lit of distilled water so that each ml. of Alum solution contains one milligram of Alum.

PROCEDURE:- Take 2 lit of sample water in all the six jars of the apparatus. Then add Alum solution in each of the six jars in varying amounts. The range of Alum dose depends upon the turbidity of the raw sample water. The normal range of Alum dose varies between 15ppm to 60ppm. Add the Alum solution to each of the six jars as per the tabular column shown in observation sheet. After adding different amounts of Alum solution in the all six jars, place the jars on the platform provided and fix the stirring paddle to the connecting rod which rotates by a gear and spindle system, with thee help of electric motor, the paddles are rotated at a speed of 30-40 rpm for about 2 minutes. The speed of the paddles are then reduced to a minimum so as to cause flocculation and stirring is continued to about 20-30 min. the rotation of paddles are then stopped and floc is allowed to settle for 30min. then pippet out the supematant from each jar and measure the turbidity using nephelometer.

GRAPH:- Plot a graph between the coagulant dose applied and turbidity of coagulated sample, by taking turbidity value on Y-axis and Alum dose on X-axis; as shown below. Then determine optimum coagulant dose from the graph which corresponds to minimum turbidity.

OBSERVATIONS:

Jar No.	Alum dose in mg/lit	ml of Alum solution to be added in 2000ml

CALCULATIONS:-

RESULTS:-

INTERPRETATION OF RESULTS:-

Determination of turbidity in water sample using nephelo turbidity meter

MEASUREMENT OF TURBIDITY USING NEPHELOMETER

AIM:- To determine the turbidity of the given sample water by Nephelometric method.

APPARATUS:- Nephelo turbidity meter.

THEORY:- Turbidity is a measure of the extent to which light is either absorbed or scattered by suspended material present in the water. Turbidity is surface waters results from the erosion of colloidal material such as clay, slit, rock fragments and metal oxides from soil, vegetable fibers and micro-organisms may also contribute to turbidity. Drinking water supplies requires special treatment by chemical coagulation and filtration before it may be used for public water supply.

            This turbidity can be brought down to required level by adding coagulants. Coagulants when added to water it will form a geletaneous substance known as floc and this will arrest the fine suspended and colloidal particles. These arrested particles will settle down rapidly because of increase in their size.

RELEVANCE:- Turbidity waters are aesthetically displeasant and are not accepted for domestic use. The colloidal matter associated with turbidity provides adsorption sites for chemicals and biological organisms that may be harmful or cause undesirable tastes and odour. Disinfection of the turbid waters is difficult and unsatisfactory, since the colloids partially shield organisms from the disinfectant. This IS values for drinking water is 10 to 25 NTU.

REAGENTS:-

1. Turbidity free water:- Pass distilled water through a lower turbidity than distilled water, discard the first 200ml, collected. If filtration does not reduce turbidity use distilled water. 
2. Stock turbidity solutions:-

i)                    Solution 1:- Dissolve 1.0 grams hydrazine suplate (NH₂)₂.H₂So₄ in distilled water and dilute it to 100 ml in a make up flask.

ii)                  Solution 2:- Dissolve 10.0 grams hexamethylene tetramine (CH₂)₆N₄ in distilled water and dilute it to 100ml.

iii)                Solution 3:- In a 100ml flask, mix 5ml. each of solution 1 and 2. Allow it to stand 24 hours, then dilute it to 100ml and mix thoroughly. The turbidity of this solution is 400 NTU.

iv)                Standard Turbidity Solution:- Take 10.0ml of solution 3 in a 100ml make up flask and dilute it to 100ml. with turbid free water. The turbidity of this suspension is 40 NTU.

PROCEDURE:-

a) Calibration of Nephelometer:-

i)                    Select proper range of NTU on Nephelometer.

ii)                  By placing distilled water in Nephelometer test tube, set the Nephelometer reading to zero by using the knobs provided for zero setting.

iii)                Using the standard turbid solution (i.e. 40 NTU), calibrate the Nephelemeter (i.e. adjust the Nephelemeter reading to 40 NTU using calibration knob)

b) Determination of turbidity of sample water:

i)                    For samples having turbidities less than 40 NTU:  Thoroughly shake the sample so as to remove any air bubbles and pour it into meter cell. Read out the turbidity of the sample from the digital display.

ii)                  For samples having turbidities above 40 NTU:- Dilute sample with 1,2 or 3 volumes of turbidity free water and convert the value obtained as below.

                 

If five volumes of turbidity free water were added to one volume of sample and the diluted sample showed a turbidity of 30 NTU, then the actual value is equal to 180 units. i.e.

                  Nephelometric turbidity units (NTU) = A(B + C)

                                                                                        C

Where

A = Turbidity found in diluted sample, B = Volume of dilution water in ml

C = Sample volume for dilution in ml.

OBSERVATIONS:-

For undiluted sample                                      For diluted sample

Digital read out =                                            Vol. of sample ( C ) =

                                                                        Vol. of dilution water ( B ) =

                                                                        Digital read out ( A ) =

CALCULATIONS:-

For undiluted sample                                      For diluted sample

Turbidity of sample in NTU =                        Turbidity in NTU = A(B + C)

                                                                                                               C

RESULTS:-

INTERPRETATION OF RESULTS:-

Determination of alkalinity

ALKALINITY

AIM:- To determine the alkalinity of the given sample water.

APPARATUS:- PH meter and Glassware.

THEORY:- The alkalinity of a water sample is its capacity to neutralize acids. Alkalinity is mainly due to presence of carbonate, bicarbonate, hydroxides and less frequently, borate’s, silicates and phosphates. It is expressed in mg/l of calcium carbonates. Two types of alkalinities are generally calculated, namely, phenolphthalein alkalinity and methyorange alkalinity. Based on these two different forms of alkalinities can be estimated. Alkalinity measurements are made by titrating the sample water with an acid and determining the hydrogen equivalent. Hydrogen ions from the acid reacts with the alkalinity according to the following equations.

                        H⁺ +  OH^- ó H2O

                        Co3^- + H⁺ ó H Co3^-

                        HCo3^- + H⁺ ó H2Co3^-

            If acid is added slowly to the water and the PH it recorded for each addition, a titration curve is obtained as shown below.

Graph

 

The significant aspects of the curve are the inflection points that occur at approximately PH8.3 and PH4.5. At PH8.3, all hydroxides and half of the carbonates are neutralized. At PH4.5, remaining half of the carbonates and bicarbonates are neutralized. Thus the amount of acid required to titrate a sample to PH4.5 is equivalent to the total alkalinity of the sample water.

RELEVANCE:- Alkalinity plays a very important role in chemical coagulation and in biological waste treatment processes, especially in aerobic digestion as this provides buffering systems. Excess alkalinity imparts a bitter taste to waste. Alkalinity is an important parameter in evaluating the optimum coagulant dosage. The permissible limit of carbonate alkalinity in domestic water supplies is 120ppm.

CHEMICAL REAGENTS:-

i)                    Standard sulphuric acid (0.02N)

ii)                  Phenolphthale in indicator

iii)                Methyl orange indicator

iv)                Sodium carbonate solution.

PROCEDURE 1:-

1. Standardization of H₂So₄ (titrant) by potentremetric titration:- Take 40ml Naco₃ solution and add 100ml distilled water. Titrate with H₂So₄ till PH of 1-2 is reached. Add acid in amounts of 0.5ml and note down the corresponding PH. Plot a graph between volume of H₂So₄ and the corresponding PH. From the graph, determine the volume off H₂So₄ at a PH of 4.5. calculate the normality of the acid using the formula.

                 

                                       A*B___

N =       53*C

Where

A = Volume of Na₂co₃ (40ml)

B = Grams of Na₂co₃ in 1 lit. = 2.5 grams

C = Volume of H₂So₄ for a PH of 4.5

Adjust the normality of H₂So₄ to 0.02N using the relation

                        N₁V₁ = N₂V₂

2. Determination of ‘P’ and ‘T’ alkalinity:- Take 25ml sample water and make it to 50ml using distilled water. Add 2 drops of phenolphthalein indicator and titrate with 0.02N H₂S0₄ till pink colour disappear. Note down the volume of H₂So₄ as V₁. To the same sample add 2 drops of methylorance indicator and titrate with H₂So₄ till colour changes to pinkish yellow. Note down the total volume of acid consumed as V.

OBSERVATIONS:-

S.No	Burette Readings		Vol. of Titrant used
	Initial	Final

Volume of acid	PH

PROCEDURE 2 :-

.Take 50 ml of sample water in a conical flask and add 3 to 4 drops of phenolphthalein indicator, color changes to pink.

.Titrate against 0.02 N HCL till colorless as end point.

. Note down the volume consumed from burette to measure phenolphthalein alkalinity. .To the same sample add 3-4 drops of methyl orange indicator and color changes to   orange.

. Titrate it against 0.02 N HCL till solution changes to pink as end point.

. Note down the volume consumed from burette to measure methyl orange alkalinity.

. The sum of phenolphthalein alkalinity and methyl orange alkalinity gives total alkalinity.

Calculations:- Total alkalinity =        V1 x 1000         +               V2  x 1000 

                                                       ml of water sample            ml of water sample

 where V1 and V2 are volume consumed from burette for phenolphthalein alkalinity and  methyl orange alkalinity.

CALCULATIONS for First Procedure:-

Phenolpthalein Alkalinity “P”  =     V1*N*50000

as mg/l caco₃                                  ml of sample

Total alkalinity “T” as mg/lit as caco₃ = V*N*50000

                                         ml of sample

Calculate the alkalinity due to various constituents using the table given below.

	Hydroxide Alkalinity	Carbonate Alkalinity	Bicarbonate Alkalinity
If P=0 If P=T/2 If P<T/2 If P>T/2 If P=T	0 0 0 (2P – T) T	0 2P 2P 2(T – P) 0	Total Alkalinity T T – 2P T – 2P 0 0

RESULT:-

GRAPH:- Plot a graph taking PH value on Y-axis and corresponding volume of acid on X-axis. From the graph obtain the volume of acid corresponding to a PH of 4.5. Also mark the inflection points (i.e. point on the graph corresponding to PH 8.3 and 4.5)

INTERPRETATION OF RESULTS:-

Estimation of chloride

 ESTIMATION OF CHLORIDES IN THE SAMPLE WATER

AIM:- To determine the concentration of chlorides in the given sample water.

APPARATUS:- Glassware.

THEORY:- Chloride is a major inorganic constituent of natural waters. Chlorides ions may be in combination with cations like calcium, magnesium, iron and sodium. Chlorides of these minerals are present because of their high solubility in water. The other sources of chlorides in the water are intrusion of sea water into fresh water bodies, pollution of industries waste and domestic wastes.

            The chloride content of water is measured by titrating the water sample with standard silver nitrate solution (AgNo₃) using potassium chromate k₂cr₂o₇ as indicator. The silver first reacts with all chlorides thereby forming silver chlorides as indicated by the following equation.

            Nacl + Agno₃ (titrant) → Agcl + NaNo₃ 

            The silver chloride so formed then reacts with potassium chromate (indicator) to form silver chromate producing reddish precipitate which indicates the end point. This reaction is indicated by the following reaction.

            2Agcl + k₂cro₄ → Ag₂cro₄ (reddish precipitate) + 2Kcl.

            The amount of silver nitrate required to produce reddish precipitate determines the amount o chlorides present in the water sample.

RELEVANCE:- The permissible limit of chloride in domestic water supplies is upto 250ppm. Although chlorides in excess of 250ppm are not harmful, but they cause unpleasant taste to water, thus rendering the water unacceptable for drinking purpose. The presence of large quantity of chlorides in water indicated its pollution due to sewage. The chloride concentrations of raw waters being used for public water supplies should therefore tested regularly, as to detect any sudden increase in their chloride content and the possibility of the organic pollution of the water source.

REAGENTS:-

1. Potassium chromate indicator:- Dissolve 10.0grams k₂cro₄ in a little distilled water. Add silver nitrate solution until a red precipitate is formed. Let stand 12 hours, filter and dilute it to 200ml with distilled water.
2. Standard silver nitrate solution (0.0141N):- Dissolve 2.395 grams AgNo₃ in distilled water and dilute it to 1000ml. standardize against 0.0141N sodium chloride solution as per the procedure described below. Store it in a brown glass bottle.
3. Standard sodium chloride (0.0141N):- Dissolve 824.1mg Nacl in chloride free water and dilute it to 1000ml.

PROCEDURE:-

1. Standardization of AgNo₃ (Titrant):- Take 20ml standard sodium chloride solution and dilute it to 100ml. add 1ml k₂cro₄ indicator. Titrate with AgNo₃ solution to pinkish yellow end point. Note down the volume of AgNo₃ consumed and determine the normality of AgNo₃ using the relation

N₁V₁ = N₂V₂

Where

N₁ = Normality of AgNo₃ (unknown)

N₂ = Normality of Nacl solution (0.0141)

V₁ = Volume of AgNo₃

V₂ = Volume of Nacl solution (20ml)

Adjust the normality to AgNo₃ to 0.0141N using the relation N₁V₁ = N₂V₂

2. Determination of chloride content in the sample water: Take a suitable volume of sample water (say 50ml) in a conical flask and dilute it to 100ml. with distilled water. Add 1ml k₂cro₄ indicator and titrate with 0.0141N AgNo₃ solution in a PH range of 7-10, to a pinkish yellow end point. Note down the volume of AgNo₃ consumed.

OBSERVATIONS:-

S.No	Burette Readings		Vol. of Titrant used
	Initial	Final

CALCULATIONS:-

                        Chloride content in mg/l = Vol of AgNo₃*N*35450

                                                                     ml of sample water

RESULTS:-

INTERPRETATION OF RESULTS:-

Determination of Total Solids

TOTAL SOLIDS

AIM:- To determine the total solids, total organic solids and total inorganic solids in the sample water.

APPARATUS:-

1. Oven or stream bath.
2. Balance
3. Crucible or dish
4. Muffle furnace.

THEORY:- The sum total of foreign matter present in water is termed as total solids. Total solids is the matter that remains as residue after evaporation of the sample and its subsequent drying at a temperature of 103 to 105⁰C. This includes the solids in suspension, colloidal and in dissolved form. The quantity of suspended solids is determined by filtering the sample of water through a fine filter and then drying and weighing the filter. The quantity of dissolved and colloidal solids is determined by evaporating the filtered water and weighing the residue. The total solids in a sample water can be directly determined by evaporating the water and weighing the residue. The total solids consists of volatile (organic) and non-volatile (inorganic or fixed). If the residue of total solids is fused in a muffle furnace, the organic compounds decompose where as only inorganic solids will remain. By weighing we can determine the inorganic solids and deducting it from total solids, we can calculate organic solids. The solids are added to water by sewage, industrial wastes, mineral content, silt, clay and organic matter.

RELAVENCE:- Solids affects the water or effluent quality adversely in a number of ways. Water with high solids concentration generally of inferior palatability, and may induce an unfavorable physiological effects on human system. Highly mineralized waters also are unsuitable for many industrial applications. The permissible amount of total solids in domestic water supplies is limited to 500ppm, although higher amounts upto 1000ppm are also sometimes permitted. Waters with very high levels of non-filterable residue may be aesthetically objectable for bathing. The determination of solids help in the design of sedimentation and coagulation units.

PROCEDURE:-

i)                    Weigh an empty dish or crucible and note down it weight as “W₁” grams.

ii)                  Measure a suitable volume of sample water and place it in a dish.

iii)                Place the dish into a steam bath or oven and evaporate the water.

iv)                Remove the dish from the oven and place it in a disiccator and allow it to cool. After it has cooled to room temperature, measure the weight of dish along with solids (i.e. residue). Let this weight be “W₂” grams.

v)                  Place the dish in the muffle furnace at a temperature of 550 + 50⁰C and ignite for 15 to 20 minutes.

vi)                Remove the dish from muffle furnace and place it in disiccator, allow it to cool to room temperature. Take the weight of the dish as “W₃” grams.

OBSERVATIONS:-

Empty weight of crucible = w₁ (g) =

Weight of crucible after evaporation water = w₂ (g) =

Weight of crucible after keeping in muffle furnace = w₃ (g) =

CALCULATIONS:-

Total solids in mg/lit =     (W₂ – W₁)*1000*1000

                                          ml of sample water

Total volatile solids in mg/lit =   (W₂ – W₃)*1000*1000

                                                       ml of sample water    

Total fixed solids in mg/lit = Total solids – Volatile solids.

RESULTS:-

INTERPRETATION OF RESULTS:-

Determination of Dissolved Oxygen (D.O)

 DISSOLVED OXYGEN

AIM:- To determine the concentration of dissolved oxygen in the sample water by Azide modification method.

APPARATUS:- Glassware along with BOD bottle.

THEORY:- Dissolved oxygen is one of the most important constituents of natural water system. A certain amount of dissolved oxygen is essential for aerobic decomposition of waste to avoid nuisance conditions in rivers and to maintain the growth of fish and other aquatic animals. Oxygen is generally absorbed by water from atmosphere and unpolluted natural surface waters are usually saturated with it. Except oxygen the presence of any other gas dissolved in water is not desirable and steps should be taken to remove the same. This test is the basis of BOD test, which is an important parameter to evaluate pollution potential of the wastes. This test determines the quality of raw water and keeps proper check on stream pollution. Dissolved oxygen in the water is determined by the modified winkler’s method, also called Azide modification method, whose principle is discussed below.

            Dissolved oxygen present in the sample water oxidizes manganous sulphate to produce manganese hydroxide (a brown colour precipitate) after addition of NAOH and KI. Upon acidification, manganese reverts to its manganous form and liberates iodine from KI, equivalent to dissolved oxygen content in the sample water. The liberated iodine is titrated against sodium thisosulphate using starch as indicator.

RELAVENCE:- The presence of dissolved oxygen in water near its saturation level is an indication of its purity. A stream must have a minimum of 2 ppm of dissolved oxygen to support fish and other higher life forms. On the other hand, high amount of dissolved oxygen corrodes the distribution system. The permissible limit of dissolved oxygen in the domestic water supplies is 5-6 ppm.

REAGENTS:-

1. Manganese sulphate solution:- Dissolve 480 grams mnso4.4H₂o in distilled water and make it to 1 lit.
2. Alkali – Iodide – Azide reagent:- Dissolve 500 gram Noah and 150 gram KI in distilled water and dilute to 1 lit. Add 10 gram sodium Azide (NAN₃) dissolved in 40ml distilled.
3. Concentrated H₂SO₄
4. Starch:- Dissolve 5grams starch in 1 lit boiling distilled water. Preserve by adding a few drops of Toluene.
5. Sodium Thiosulphate solution: Dissolved 6.205 grams Na₂s₂o₃.5H₂o in distilled water and dilute it to 1 lit. Standardize it using potassium dichromate solution.
6. Standard potassium dichromate solution:- Dissolve 1.226 grams K₂CR₂O₇ in distilled water and dilute it to 1 lit.
7. Potassium Iodide Solution:- Dissolve 20 grams KI in 100ml distilled water.

PROCEDURE:-

1. Standardization of sodium Thiosiphate Titrant:-

a)      Take 100 ml distilled water in a flask and add 10ml KI solution. Add 10ml 1+9 H₂SO₄.

b)      Add 20ml K₂CR₂O₇ solution and store it in a dark place for five minutes.

c)      Titrate with Na₂s₂o₃ titrant, adding starch towards the end when a pale straw colour develops. Continue titration to colourless end point. Note down the volume of titrant used.

d)     Determine the normality of titrant using the relation N₁V₁ = N₂V₂

N₁ = normality of K₂CR₂O₇ = 0.025

V₁ = volume of K₂CR₂O₇ – 20ml

V₂ = volume of Titrant consumed

N₂ = normality Titrant (unknown)

Adjust the normality of Titrant to 0.025N using the relation N₁V₁ = N₂V₂.

2. Estimation of D.O. in the sample water:-

a)      To the sample in the BOD bottle, add 2ml manganese sulphate solution, 2ml of alkali azide reagent, well below the surface.

b)      Stopper and mix by inverting bottle at least 15 times. Let the brown ppt settle for 5 minutes.

c)      Add 2ml conc. H₂So₄ and stopper. Gently invert to dissolve the ppt totally.

d)     Take 203ml of the bottle water in the flask and titrate with sodium thiosulphate titrant.

e)      Add 1-2 ml starch and continue titration till the first disappearance of pale blue colour.

  

OBSERVATIONS:-

S.No	Burette Readings		Vol. of Titrant used
	Initial	Final

CALCULATIONS:-

   D.O. in mg/l = ml of 0.025N sodium thiosulphate used.

RESULTS:-

INTERPRETATION OF RESULTS:-

Estimation of total hardness and calcium hardness in water sample

 ESTIMATION OF TOTAL HARDNESS AND CALCIUM HARDNESS IN THE SAMPLE WATER

AIM:- To determine the total hardness, calcium and magnesium hardness in the given sample water.

APPARATUS:- Glassware.

THEORY:- Hardness of water is mainly caused by divalent cations. They are capable of reacting with soap to form precipitates and with certain an ions to form scales. Calcium and magnesium ions are the principal hardness causing ions in natural water, even through irons, manganese, strontium and ferrous can contribute to some extent, ferric and aluminum ions can cause hardness but their solubility at the PH of natural waters are so small that they can be considered as insignificant.

            Hardness in water is derived largely from contact with soil and rocks which leads to the solubilization of limestone and other materials. Hardness is normally expressed as mg/l of CaCo₃. Hard waters are not associated with any health hazards. However, they have comparatively higher dissolved solids and cause problems of left out residues on kitchen utensils and glassware and are unfit for bathing and laundry purposes due to high consumption of soap. Hard waters are unfit for certain industries like textiles and beverages and are not suitable for boiler feed.

Hardness is classified in two ways.

i)                    With respect to the metallic ions and

ii)                  With respect to anions associated with metal ions. Calcium and magnesium are, as mentioned earlier, the principal ions associated with hardness. In some cases, it is necessary to know ca⁺² and mg⁺²  hardness individually. In such cases, total hardness and hardness associated with either calcium (or magnesium) are determined. Then,

Total harness – calcium hardness = magnesium hardness.

            The part of total hardness associated with carbonate and bicarbonate alkalinities present in water is considered as carbonate hardness or temporary hardness, as they can be caused to precipitate by prolonged boiling. Since alkalinity and hardness are expressed as mg/l caco₃, the carbonate alkalinity can be obtained as follows.

Case 1:- When total hardness is greater than alkalinity, then calcium

Hardness = alkalinity, and

Case 2:- When total hardness is greater than or equal to alkalinity then carbonate Hardness = total hardness and non – carbonate hardness = 0

            Non carbonate hardness is also called permanent hardness as they cannot be removed by boiling and are associated with sulphates, chlorides and nitrates anions. Hardness can be measured directly by titration with ethylene diamine tetra acetic acid(EDTA) using eriochrome black T(EBT) as indicator. The EBT reacts with the divalent metallic ions, forming a complex that is red in colour. The EDTA replaces the EBT in the complex and when the replacement is complete, the solution changes from red to blue. This is shown by the reactions shown below.

 __           __                                             __            __

│   Ca++    │              +      EBT       =   │  Ca EBT   │

│                │                                          │                  │  complex. (wire red)

│_ Mg++ _│                                          │_ Mg      __│

 __           __                                                _                _

│ Ca EBT  │                                             │ Ca EDTA │

│                │ Complex + EDTA =           │                  │  complex EBT (pale blue

│_ Mg     _│                                             │  Mg         _│                           endpoint)

RELAVENCE:- Hard waters are not associated with any health hazards. However they have comparatively higher dissolved solids and cause problem of left out residues on kitchen utensils and glassware’s and unfit for bathing and laundry purposes due to high consumption of soap. Hard waters are unfit for certain industries like textiles and beverage and not suitable for boiler use. The permissible limit of total hardness for domestic use is upto 300 ppm. The scale of hardness showing different levels of hardness of water is as follows.

         Range (mg/l)                                          Hardness Level

         

         0-50                                                        Soft

         50-100                                                    Moderately soft

         100-150                                                  Slightly soft

         150-250                                                  Slightly hard

         Above 250                                             Hard

CHEMICAL REAGENTS:-

1. BUFFER 1 (for total hardness): To 50ml distilled water, add 1.179 grams disodium salt of EDTA and 780mg. Mgso₄.7H₂o. To this solution, add 16.9 grams ammonium chloride and 143 ml. concentrated ammonium hydroxide and dilute it to 250ml using distilled water.
2. BUFFER 2 (for calcium hardness):- Dissolve 40 grams NaoH in a small quantity of distilled water and make it to 1 lit.
3. EDTA ( Disodium salt) solution 0.01N:- Dissolve 3.723 grams EDTA (Disodium salt) in distilled water and make it to 1 lit.
4. Standard Hard water(0.01N):- Take 1.0 gram caco3 (calcium carbonate) and dissolve it in 1+1 Hcl. Add 200ml distilled water and boil it for a few minutes. After cooling, add distilled water and make it to 1 lit.
5. Eriochrome Black T(EBT) for total hardness.
6. Muroxide (for calcium hardness)

PROCEDURE:-

1. Standardization of EDTA using standard hard water of 0.01N:- Take 25ml standard hard water and make it to 50 ml by adding distilled. Add 1-2ml buffer (1), so as to adjust the PH above 10. then, add a pinch of EBT indicator. The solution turns to wine red. Titrate the solution with given EDTA solution till the colour turns to pale blue. Note down the volume of EDTA consume, and determine the normality of EDTA using the relation

N₁V₁ = N₂V₂

Where

N₁ = normality of EDTA (unknown)

V₁ = volume of EDTA consumed

N₂ = normality of standard hard water = 0.01

V₂ = volume of standard hard water = 25ml

Adjust the normality of EDTA to 0.01N using the relation N₁V₁ = N₂V₂

2. Determination of total hardness in the sample water:- Take 50ml sample water in a conical flask and add 1-2ml buffer (1) solution. Add a pinch of EBT indicator. The sample turns to wine red. Titrate the sample with 0.01N EDTA till the colour turns to pale blue. Note down the volume of EDTA consumed.
3. Determination of calcium hardness in the sample water:- Take 50ml sample water in a conical flask and add a suitable amount of buffer (2) so as to increase PH to 12-13, add a pinch of muroxide indicator. Titrate with 0.01N EDTA till colour turns to pale purple. Note down the volume of EDTA consumed.

OBSERVATIONS:-

S.No	Burette Readings		Vol. of Titrant used
	Initial	Final

CALCULATIONS:-

Total Hardness in mg/lit as caco₃ =   A * B * 1000

                                                         ml of sample water

Calcium Hardness in mg/lit as caco₃ =        A *  B___

                                                               ml of sample water

where

A = ml of EDTA consumed

B = ml of EDTA equivalent to 1mg of caco₃ = 1

(since 1mg of caco₃ is equivalent to 1ml of 0.01N EDTA)

Magnesium Hardness = Total Hardness – Calcium Hardness.

RESULT:-

Total Hardness             =

Calcium Hardness        =

Magnesium Hardness   =

INTERPRETATION OF RESULTS:-