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Estimation of Chlorides in any water body ( Pond water)

Submitted By: Sadia Rahat (15) MS

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Table of ContentsGRAVMETRIC ANALYSIS...............................................................................................................................2

TYPES OF GRAVIMETRIC TECHNIQUES.........................................................................................................2

CHLORIDES..................................................................................................................................................2

PERMISSIBLE LIMITS OF CHLORIDE IN DIFFERENT WATER BODIES..............................................................3

EQUIPMENTS NEEDED.................................................................................................................................3

METHOD......................................................................................................................................................4

PROCEDURE.................................................................................................................................................4

OBSERVATION AND CALCULATION..............................................................................................................5

Result...........................................................................................................................................................7

Thus, there are about 0.297% of chlorides present in our pond water sample...........................................7

PRECAUTIONS..............................................................................................................................................7

ENVIRONMENTAL SIGNIFICANCE................................................................................................................7

ENVIRONMENTAL IMPACTS.........................................................................................................................7

REFERENCE..................................................................................................................................................8

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GRAVMETRIC ANALYSISIt is the quantitative determination of an analyte based on the mass of a solid. In this

technique we usually use an excess of added reagent reacts with the analyte to form a precipitate. The precipitate is filtered, dried, and weighed. Its mass is used to calculate the concentration of the analyte in the given sample.

TYPES OF GRAVIMETRIC TECHNIQUESGravimetry is one of only a small number of definitive techniques whose measurements

require only base SI units, such as mass or the mole, and defined constants, such as Avogadro’s number and the mass of 12C. There are usually four types of gravimetric techniques.

Electro-gravimetric technique Volatilization gravimetric technique Precipitation gravimetric technique

In our particular problem, we are going to use precipitation Gravimetric technique. In precipitation gravimetry an insoluble compound forms when we add a precipitating reagent, or precipitant, to a solution containing our analyte. In most methods the precipitate is the product of a simple metathesis reaction between the analyte and the precipitant; however, any reaction generating a precipitate can potentially serve as a gravimetric method (Summerfield and Reid, 2010).

Range of analytes can be detected and estimated through gravimetric techniques such as SO4 can be analyzed through barium chloride, Cl- etc.

PROBLEM: ESTIMATE THE AMOUNT OF CHLORIDES IN THE GIVEN WATER BODY (POND WATER) SAMPLE.

We use gravimetric technique to determine the chloride ion concentration of pond water solution by gravimetric analysis. A precipitate of silver chloride is formed by adding a solution of silver nitrate to the aqueous solution of chloride ions. The precipitate is collected by careful filtration and weighed.

Ag+ + Cl–→ AgCl(s)

CHLORIDESEarth crust usually contains about 0.05% of chlorides in it. Chlorides are present in

almost every kind of waterbody such as ground water, canal water, aquifers etc. Normal

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concentration of chlorides in fresh water body is about 1-100ppm. However sea water usually contains 35,000ppm chlorides.

Some of the plants and microorganisms are adapted to live in brackish (mixed fresh and salt) water. but once chlorides entered in water body it is really difficult to remove them thoroughly, even water treatment plants are not able to remove them hundred percent. The excess of salt in water bodies may threaten the biological integrity of aquatic ecosystems (Robertson et al., 1938).

PERMISSIBLE LIMITS OF CHLORIDE IN DIFFERENT WATER BODIES

National environmental Quality Standard for municipal and industrial effluents in PakistanSr. No Parameter mg/L1 Chloride (Cl-) Existing Standard 10002 Chloride (Cl-) Into Wetland Waters 10003 Chloride (Cl-) Into Sewage Treatment 1000

NEQS, 2008

Standards for Quality Drinking Water in PakistanSr. No. Parameter mg/L1 Standard values of Chloride (Cl-) for Pakistan <2502 Standard values of Chloride (Cl-) according

to WHO guideline250

3 Standard values of Chloride (Cl-) according to USA guideline

250

WHO, 2003EQUIPMENTS NEEDED

Analytical Balance pipettes 250 mL conical flask Bunsen burner

Measuring cylinders Whatman filter paper 41 Filtering Flask Stirrer

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METHODSAMPLE PREPARATION

We filtered sample water to remove all kind of impurities that were present in the form of sand or grit particles. We filter 20 ml sample water.

REAGENTS PREPARATION0.1 M Silver Nitrate (AgNO3) in 150ml Distilled Water

We carefully weigh 2.54grams of silver nitrate through analytical balance. Dissolve it in 150 ml distilled water. This is our 0.1 molar solution of AgNO3.

1M solution means mass of one mole of AgNO3 is dissolved in 1000ml of Solution. So,Molar mass of AgNO3 = 107.8682 + 14 +48 = 169.8682g/mole1M solution of AgNO3 contains=169.8682 g of AgNO3/1000ml of solution0.1M solution of AgNO3 contains = 169.8682 × 0.1=16.9868 g of AgNO3/1000ml of solution

But, here the volume of solution is restricted to 150ml so we will adjust the mass of AgNO 3

according to this.0.1 M solution in 1000ml require the mass of AgNO3= 16.9868gSo, 1ml require the mass of AgNO3 =16.9868/1000mlAnd 150ml require the mass of AgNO3 =16.9868g/1000ml ×150ml

=2.54g of AgNO3/150ml of solution

We carefully weigh 2.54grams of silver nitrate through analytical balance. Dissolve it in 100 ml distilled water. Mixed well with the help of stirrer and made the final volume upto 150ml. This is our 0.1 molar solution of AgNO3.

PROCEDUREFirst of all, we carefully washed all the apparatus with distilled water. Then we carefully

weigh the mass of filter paper by using analytical balance. It is about 1.07 grams. Then we take 4.5 ml AgNO3 by using pipette and add it into 20 ml sample water. During the addition of AgNO 3

we continuously shake sample water, so that precipitates could form properly. Then we add 5 ml AgNO3 by using pipette and add it in sample water. We add 5ml more AgNO3 by using pipette and add it in sample water. Then we filter our sample to collect precipitates formed.

The same process is repeated on the filtrate until we reach a level where no precipitates are formed on addition of silver nitrate. This represents that all the chloride ions in the solution have been precipitated out. Then we collect the precipitates formed on previously collected filter paper.

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To check if any other chloride present in our water body, we again add 10 ml AgNO3 by using pipette and add it in sample water. No precipitate form this time. Then we dried up filter paper and weigh it. This is the mass of filter paper plus precipitates. We subtract the mass of filter paper from this mass. This is the mass of chlorides precipitates.

OBSERVATION AND CALCULATIONSr.No Sample

Volume(ml)

Weight of dry filter paper(g)

A

Weight of dry filter paper + precipitates (g)

B

Weight of precipitates

C=B-A1. 20 1.07 1.31 0.24

2. 20 1.07 1.30 0.23

3. 20 1.07 1.32 0.25Average weight of filter paper+ precipitates=1.31g

Weight of filter paper =1.07g

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Weight of filter paper and precipitates = 1.31g

Weight of precipitates = 1.31g-1.07g= 0.24g/20ml of sample

Ag+ + Cl–→ AgCl(s)

The above mentioned equation shows that one mole of Ag reacts with one mole of Cl. It means that one mole of AgCl contains one mole of silver (Ag) as well as one mole of chloride (Cl).

Atomic mass of Silver (Ag) =107.8682g

Atomic weight of Chlorine (Cl) = 35.5 g

Grams of AgCl in sample = Weight of precipitates =0.24g

Molecular/Molar mass of Silver Chloride (AgCl) = 107.8682g + 35.5g =143.3982g/mole

Moles of Chloride = Moles of AgCl = Grams of AgCl(S)

Molar mass of AgCl

“So we can write as”

Moles of Chloride = Grams of AgCl(S)

Molar Mass of AgCl

By putting the values

Moles of Chloride = 0.24g = 0.0016737 moles of Cl/20ml of sample

143.3982g/mole

To get the grams of Cl we will use the following formula

Moles of Cl = Grams of Cl

Molar Mass of Cl

Grams of Cl=Moles of Cl × Molar Mass of Cl

Grams of Cl= 0.0016737× 35.5= 0.0594g Cl/20ml of sample

%age of Cl in sample = Gramsof Cl∈sampleVolumeof sample

∗100

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= 0.0594 gCl

20ml∗100

= 0.297 % of chloride present in pond water sample

a) Changing g to mg0.059 * 1000 = 59 mg/20 ml

b) 20 ml of sample (pond water) contain Cl- ion = 59 mg1 ml of sample contain Cl- ion = 59/201000 ml of sample contain Cl- ion = 59/20 * 1000

= 2,950 mg/L or 2,950 ppm

Result

Thus, there are about 0.297% of chlorides present in our pondwater sample.Concentration of

chlorides in our water sample is 2950 ppm. This is higher than the permissible limits which are 250 ppm

in drinking water according to WHO standards. The permissible limit of chlorides in municipal wetland

water is about 1000ppm, so the concentration of chlorides in our water sample is higher than both of

the standards limit.

PRECAUTIONSWe have stored silver nitrates in a bottles cover with brown paper so that it cannot

expose to sun light. We carefully handle the silver nitrate; otherwise it may cause skin irritation and leave its scars on skin. We have washed our whole apparatus to the distilled water to remove impurities.

ENVIRONMENTAL SIGNIFICANCEChloride implies salty taste in water bodies. So in the areas where the water resources

are scarce, water bodies which contain more than 2000ppm sodium chloride concentration used as domestic source of salts (Hunt et al., 2012).

Another significant aspect of chloride is that it is use for the chlorination of drinking water, as it acts as anti-septic and kills harm full bacteria.Appropriate quantity of chlorides is too much essential for human body. Low concentration of sodium chloride affects the human endocrinal system (Hunt et al., 2012).

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ENVIRONMENTAL IMPACTSThe anthropogenic increase in chlorides concentration in different waterbodies causes

many environmental impacts. It threatens the biological integrity of aquatic ecosystems. There are a variety of sources, causes increase in concentration of chlorides in aquatic water bodies (Hunt et al., 2012).

Chlorides used as road salts for the purpose of deicing caused abrupt increase in chlorides concentration in water bodies. Chlorides use as an active ingredient in the form of sodium chloride or potassium chloride, and when snow beings to melt in summers; the spikes in roadside streams causes increase in concentration of chloride in drain water (Hunt et al., 2012).

Chlorides normally use in the form of sodium chloride, in water softeners. These water softeners causes increased salt concentration in septic systems. Chlorides also have the ability of corrosions, if present in excessive quantity. Industrial boilers negatively affected by salts depositions and their life time decreases as well (Hunt et al., 2012).

REFERENCE Robertson, J.D. and Webb, D.A. (Nov, 1938). The Micro Estimation of Sodium, Potassium,

Calcium, Magnesium, Chloride and Sulphate in Sea Water and The body Fluids of Marine

Animals. Department of Zoology. Pg. 155-172

World Health Organization. (2003). Chloride in Drinking Water: WHO Guidelines for Drinking

Water-Quality 2(2).

Hunt, M., Herron, E. and Green, L. (March, 2012). Chlorides in Fresh Water. The University

of Rhode Island.

Summerfield, S. Reid, H. (April, 2010). Introduction to Analytical Chemistry.

Dil, S.A., Qazi, I.A., Baig, M.A., Khan, E.A. and Tahir, A. (June, 2008). National Standards for

Drinking Water Quality. Government of Pakistan. Pakistan Environmental Protection

Agency.

Environmental Fact Sheet. WD-DWGB. (2010). Sodium and Chloride in Drinking Water. New

Hemisphere.03301