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.