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CHEMISTRY LABORATORY MANUAL(FOR B.Sc. APPAREL AND FASHION TECHNOLOGY)(09F107 APPLIED SCIENCES LABORATORY)

NAME ROLL No. BRANCH

: : : I sem. APPAREL & FASHION TECHNOLOGY

DEPARTMENT OF CHEMISTRY

PSG COLLEGE OF TECHNOLOGYCOIMBATORE-641004

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LIST OF EXPERIMENTS1. Determination of strength of commercial acid and purity of washing soda 2. Estimation of available chlorine in hypochlorite solution 3. Determination of total, temporary, calcium and magnesium hardness of water by EDTA method 4. Estimation of strength of hydrogen peroxide 5. Determination of chemical oxygen demand of a water sample

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CONTENTSObserv ation Marks (20) Record Marks (05) Total Marks (25) Sign of the Faculty

Ex. No 1.

Date

Title of the Experiment

Page No

2.

3.

4.

5.

CA -I Marks out of 12.5 CA - II Marks out of 12.5 TOTAL

= = =

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Required Laboratory Materials 1. Laboratory Manual for Applied sciences laboratory 09F107 2. A laboratory record notebook covered with brown sheet, which must be hard bounded, it must not be spiral bound notebook. 3. A scientific electronic calculator and other writing tools. General rules of Laboratory safety 1. The chemicals used in this laboratory are likely corrosive and/or toxic. Avoid contact with your skin of any of these chemicals. It contact does occur; copiously wash the area of contact with water. 2. Do not perform any unauthorized experiments. 3. Students at this level must not work alone in this laboratory. 4. Adequate foot covering is required at all times. Do not wear sandals. Do not come into the laboratory with bare feet. 5. Cold and hot objects often look the same. Remember always to exercise caution when picking up laboratory glassware and tools. 6. Always notify the instructor in case of an injury. 7. As for the disposal of waste chemicals, when in doubt ask the instructor. 8. If you spill any reagents, clean them up immediately, if necessary rinse well with water. 9. Keep your desk and reagent table clean and tidy at all times. At the end of the experiment clean the apparatus and the table. Return the reagent bottle to the lab assistants. 10. Dispose the solid waste in waste basket not in the sink. 11. If you break any glassware inform immediately to the lab assistants. 12. Do not place bags or books on the lab benches. Keep them on the tables provided for this purpose.

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General instructions 1. Your laboratory manual is considered as a proof of the laboratory work you done. Keep it neat and all pages intact. 2. While in laboratory, you should know what you are doing and why you are doing so. In order to avoid unnecessary repetition of the experiments and loss of time, proper preparation before starting the experiment is imperative. 3. Read the principle and experimental procedure of assigned experiment. 4. Plan the programming of your experiment in such a way as to be completed within the allotted time. 5. Experiment number and date should appear at the beginning of every experiment. 6. All entries must be made directly with a non-erasable ink/ball pen. 7. Under no circumstances should any pages be removed from the record notebook. 8. Do not use correction fluid, liquid paper, white-out or any product that covers up original entries. Do not over write the readings in the laboratory manual. 9. Your record notebook will not be collected until the end of the course. It will then be graded based on the criteria outlined above. 10. Plan the organization of the data in your note book. 11. Write all observations/readings only in the observation note book. 12. All lab notebook entries must be signed by your course instructor before leaving from your Laboratory after completion of the experiment.

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Quantitative analysis It involves the determination of the quantity of a substance in a give sample. There are three different types of quantitative analysis i) Volumetric analysis ii) Gravimetric analysis iii) Instrumental analysis i) Volumetric analysis: Volumetric analysis makes use of a reaction between two substances; the reaction may be of acid base type, redox type etc. The known volume of a substance in the form of a solution is allowed to react with the other and the completion of the reaction is detected by the use of suitable indicator. The volume of the second substance is measured. From the volumes of these two substances the strengths are calculated. Volumetric analysis makes use of the following reactions: (i) Acid-base (ii) oxidation-reduction (iii) precipitation reaction etc. For volumetric analysis the solutions are to be prepared of known strengths. For this purpose two types of solutions are considered. i) Primary standard ii) Secondary standard Primary standard solution: A solution of known strength with primary standard substance is known as a primary standard solution. A primary standard substance remains unchanged in solution for a reasonable length of time. The characteristics of primary standard substance: It should be i) obtained in a high degree of purity ii) stable and not affected by water ii) readily soluble in water and it should not be deliquescent Example of primary standard substances: i) oxalic acid

ii) anhydrous sodium carbonate iii) potassium dichromate iv) sodium chloride etc. A substance, not possessing above characteristics is a secondary standard substance eg. Hydrochloric acid, sodium hydroxide, potassium permanganate etc. Their strengths are determined by titrating them against a primary standard solution. The strength of a secondary

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standard solution do not remain unchanged on keeping. Their strengths should be determined when the experiments are carried out. For preparation of a primary standard solution one should weigh a substance accurately, and this is very vital for quantitative analysis. General instructions for volumetric work During their way to volumetric analysis, students often miss to do such a vital thing at any stage of the work which leads to a total wrong result; even doing the experiment for the whole day, his work become waste. The following instruction, in that sense, is very important. In general both inside and outside of all the apparatus used for volumetric analysis should be perfectly clean. It should be washed with distilled water. i) The conical flask should be washed with distilled water thoroughly. ii) pipette should be rinsed twice with pipette solution and the solution should be thrown in the basin. iii) burette should be washed twice with the burette solution and the washings should be thrown in the basin. Then the burette is filled with the burette solution, no air bubble should be left at the mouth of the jet and there is one continuous liquid level from the end of the jet to the mark at the top. iv) students should be very much careful with these solution, these solutions in no case, should get diluted even with a single drop of water during the work. Indicators Indicators play a vital role I the volumetric analysis. The end point of a reaction is determined by an indicator. Indicator changes its colour with slight excess of one of the reactants, which is generally added during titration from the burette. Indicators fall into three main classes i) internal indicator (eg. acid-base indicators like phenolphthalein, methylorange etc.) ii) external indicator (eg. potassium ferricyanide) iii) self indicator (eg. potassium dichromate) internal indicators are added to the titrating vessel. External indicators are used outside the titration vessel. That is why, use of external indicators leads not to a very accurate result. Self indicators are one the reactants itself.

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Determination of strength of commercial hydrochloric acid Standard sodium carbonate Vs Commercial hydrochloric acid Burette solution Pipette solution Indicator Endpoint : Commercial Hydrochloric acid : Standard sodium carbonate : Methyl orange : Golden yellow to orange red

S.No 1. 2.

Volume of standard Na2CO3 solution(ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of HCl (ml)

Concordant value = Calculation: Volume of standard Na2CO3 solution Normality of standard Na2CO3 solution Volume of HCl solution Normality of HCl solution V1 N1 V2 N2 = = = = V1N1 / V2 20 ml N ml

ml

= Strength of Commercial acid solution = N2 x 100

N

=

N

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Ex. No: Date: DETERMINATION OF STRENGTH OF COMMERCIAL ACID AND PURITY OF WASHING SODA AIM: To determine the percentage purity of the chemical before application to ensure uniform and quality process. PRINCIPLE: Both estimations are based on the acid-base neutralization principle. Hydrochloric acid reacts with sodium carbonate/washing soda and gives sodium chloride, carbondioxide and water. 2HCl PROCEDURE: Preparation of standard (0.1N) sodium carbonate Exactly 0.53g of Na2CO3 (AR grade), is weighed and dissolved in distilled water. The solution is made up to 100ml using a standard measuring flask. ESTIMATION OF HCl The commercial hydrochloric acid is diluted to 100 times to make it suitable for estimation. Fill the burette with diluted hydrochloric acid solution. Exactly 20ml of standard sodium carbonate solution is pipette out into a clean 250ml conical flask. To this, two drops of methyl orange indicator is added and the solution is titrated against the hydrochloric acid filled in the burette. End point is the colour change from golden yellow to orange red. The titration is repeated till the concordant values are obtained. From the obtained values the strength of commercial hydrochloric acid can be calculated. + 2Na2CO3 2NaCl + H2O + CO2

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Determination of purity of washing soda Hydrochloric acid Vs Washing soda sample Burette solution Pipette solution Indicator Endpoint : Hydrochloric acid : Washing soda solution : Methyl orange : Golden yellow to orange red

S.No 1. 2.

Volume of washing soda solution(ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of HCl (ml)

Concordant value = Calculation: Volume of HCl solution Normality of HCl solution Volume of Washing soda solution Normality of Washing soda solution V3 N2 V4 N4 = = = = V3N2 / V4 20 ml

ml

N (from previous titration) ml

= Weight of washing soda taken Weight of washing soda (Na2CO3) in whole of the given solution

N W W1 = ___________g = (N4 x 53)/10

Percentage purity of given washing soda sample

= (W 1/W) x 100

=

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DETERMINATION OF PURITY OF WASHING SODA

About one gram of washing soda sample is accurately weighed. It is dissolved thoroughly using distilled water and made up to 100ml using a standard measuring flask. Fill the burette using hydrochloric acid solution. Exactly 20ml of made up washing soda solution is pipette out into a clean 250ml conical flask. To this, two drops of methyl orange indicator is added and the solution is titrated against the hydrochloric acid filled in the burette. End point is the colour change from golden yellow to orange red. The titration is repeated till the concordant values are obtained. From the obtained values the strength of given washing soda solution can be calculated.

RESULT:

1) Strength of given commercial acid

=

N %

2) Purity of given washing soda sample =

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Titration I:

Standardization of sodium thiosulphate solution Vs Sodium thiosulphate

Potassium dichromate Burette solution Pipette solution Indicator Endpoint Special Condition

: Sodium thiosulphate : Standard Potassium dichromate : Starch : Disappearance of blue colour : Added one test tube of dil. Sulphuric acid and 10ml 5% KI

S.No

Volume of standard K2Cr2O7 solution (ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of Sodium thiosulphate (ml)

1. 2.

Concordant value = Calculation: Volume of standard K2Cr2O7 solution Normality of standard K2Cr2O7 solution Volume of sodium thiosulphate solution Normality of sodium thiosulphate solution V1 N1 V2 N2 = = = = V1N1 / V2 20 ml N ml

ml

=

N

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Ex. No: Date: ESTIMATION OF AVAILABLE CHLORINE IN HYPOCHLORITE SOLUTION AIM: To determine the percentage of available chlorine in the given commercial hypochlorite solution, being supplied with a standard solution of potassium dichromate and sodium thiosulphate solution as link solution. PRINCIPLE: Commercial hypochlorite solution (eg. Bleaching powder) is a mixture of

CaOCl2.CaCl2.Ca(OH)2.H2O, etc., On treatment with dilute acids chlorine gas is liberated. CaOCl2 + 2CH3COOH (CH3COO)2Ca + H2O + Cl2 The chlorine gas thus liberated reacts with KI to give iodine. The liberated iodine is titrated against sodium thiosulphate using starch as indicator. 2KI + Cl2 I2 + 2Na2S2O3 PROCEDURE: TITRATION I: STANDARDIZATION OF SODIUM THIOSULPHATE SOLUTION 50ml burette is washed with distilled water rinsed and filled with sodium thiosulphate solution. A 20ml pipette is washed with distilled water and rinsed with the standard potassium dichromate solution. Exactly 20 ml of potassium dichromate solution is pipetted out into a clean 250ml conical flask. To this one test tube full of dil.sulphuric acid and 10ml of 5% KI solution are added. The liberated iodine is titrated against thiosulphate solution. When the solution turns yellow, 1ml of starch solution is added and the titration is continued. The end point is the disappearance of blue colour. The titration is repeated for concordant values. From the titre value, the normality of sodium thiosulphate solution can be calculated. 2KCl + I2 2NaI + Na2S4O6

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Titration II: Estimation of chlorine in hypochlorite solution Sodium thiosulphate Burette solution Pipette solution Indicator Endpoint Special Condition Vs Hypochlorite solution

: Sodium thiosulphate : hypochlorite solution : Starch : Disappearance of blue colour : add 10ml of acetic acid and 10ml of 5% KI

S.No

Volume of standard hypochlorite solution (ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of Sodium thiosulphate (ml)

1. 2.

Concordant value = Calculation: Volume of sodium thiosulphate solution Normality of sodium thiosulphate solution Volume of hypochlorite solution Normality of hypochlorite solution V1 N1 V2 N2 = = = = V1N1 / V2 20 ml N ml

ml

=

N

Weight of hypochlorite in 250ml of the given suspension (W 1)

=

g

The amount of chlorine present in the whole of the given solution (W 2) = (N2 x 35.5)/4

= Percentage of available chroline = W1 / W2 =

g

= weight of chlorine present / weight of hypochlorte taken

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TITRATION II: ESTIMATION OF AVAILABLE CHLORINE The burette is filled with thiosulphate solution. Pipette is thoroughly washed with distilled water rinsed with the given hypochlorite solution. 20ml of the given hypochlorite is pipette out into a clean conical flask. About 10ml of dil. Acetic acid and 10ml of 5% KI solution are added and the solution turns dark brown in colour due to liberation of iodine. The liberated iodine is titrated agains thiosulphate solution until the solution becomes straw yellow in colour. At this stage 1ml of starch solution is added as indicator and the solution turns dark blue in colour and the titration is continued. End point is the disappearance of blue colour. The titration is repeated for concordant values. The normality of bleaching powder (hypochlorite) with respect to chlorine and the amount of chlorine present in the whole of the given sample can be calculated.

RESULT: i) The amount of chlorine present in the whole of the given solution is _________g

ii) Percentage of available chlorine in the given hypochlorite sample solution is ________g

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Titration I:

Standardization of potassium permanganate solution Vs Potassium permanganate

Standard Oxalic acid Burette solution Pipette solution Indicator Endpoint Special Condition

: Potassium permanganate : Standard Oxalic acid : Self : Appearance of permanent pale pink colour : Add one test tube full of dil.sulphuric acid and heat to bearable warmth

S.No

Volume of standard oxalic acid solution (ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of potassium permanganate (ml)

1. 2.

Concordant value = Calculation: Volume of standard oxalic acid solution Normality of standard oxalic acid solution Volume of potassium permangante solution Normality of potassium permanganate solution V1 N1 V2 N2 = = = = V1N1 / V2 20 ml N ml

ml

=

N

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Ex. No: Date: ESTIMATION OF STRENGTH OF HYDROGEN PEROXIDE AIM: To determine the strength of H2O2 in volume and to estimate the amount of H2O2 present in the whole of the given commercial sample. You are supplied with a standard solution of oxalic acid containing ________g/________ml and an approximately decinormal solution of KMnO4 solution. PRINCIPLE: Hydrogen peroxide is oxidized by an acid solution of KMnO4 2KMnO4 + 3H2SO4 5H2O2 + 5[O] 2KMnO4 + 3H2SO4 + 5H2O2 PROCEDURE: TITRATION i: STANDARDIZATION OF POTASSIUM PERMANGANATE 50ml burette is thoroughly washed with distilled water rinsed and filled with the given KMnO4 solution. 20ml pipette is thoroughly washed with distilled water rinsed with the given standard oxalic acid. Exactly 20ml of the standard oxalic acid solution is pipette out into a clean 250ml conical flask and one test tube full of dil.sulphuric acid is added. The mixture is heated to bearable warmth. The solution is then titrated against potassium permanganate taken in the burette. The end point is the appearance of a permanent pale pink colour in the solution. The titration is repeated till concordant values are obtained. From the titre value, the strength of potassium permanganate is calculated. K2SO4 + 2MnSO4 + 3H2O + 5[O] 5H2O + 5O2 K2SO4 + 2MnSO4 + 8H2O + 5O2

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Titration II: Estimation of hydrogen peroxide solution Potassium permanganate Burette solution Pipette solution Indicator Endpoint Special Condition Vs Hydrogen peroxide solution

: Potassium permanganate : Hydrogen peroxide : Self : Appearance of permanent pale pink colour : Add one test tube full of dil.sulphuric acid

S.No

Volume of H2O2 solution (ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of potassium permanganate (ml)

1. 2.

Concordant value = Calculation: Volume of potassium permangante solution Normality of potassium permanganate solution Volume of H2O2 solution Normality of H2O2 solution V1 N1 V2 N2 = = = = V1N1 / V2 20 ml N ml

ml

= Strength of original hydrogen peroxide N3

N

= N2 x dilution factor = = N 5.6 volumes (5.6/1) x N3 volumes (N2 x 17) / 10

1N H2O2 N3 N H2O2

= = =

Amount of hydrogen peroxide present in the whole of the given commercial sample

=

g

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TITRATION II: ESTIMATION OF HYDROGEN PEROXIDE SOLUTION The given hydrogen peroxide solution is made upto 100ml in a standard measuring flask and the solution is shaken well for uniform concentration. 20ml of the made up hydrogen peroxide solution is pipette out into a clean conical flask. About 20ml of dil.sulphuric acid is transferred into it. The contents of the conical flask are titrated against KMnO4 till the appearance of permanent pale pink colour. The titration is repeated for concordant values. The normality of H2O2 and the amount of H2O2 present in the whole of the given H2O2 sample are calculated.

Note: H2O2 H2O + O2 34g of H2O2 on heating gives 16g of oxygen 17g of H2O2 on heating gives 8g of oxygen 1 litre of 1N H2O2 solution (eq.mass is 17) on heating gives 8g or 5.6 litres of oxygen. i.e. 1N H2O2 = 5.6 volumes

RESULT: i) The strength of given commercial sample of hydrogen peroxide sample is _______volumes ii) Amount of hydrogen peroxide present in the whole of the given commercial sample is _______g of H2O2

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Titration I:

Standardization of EDTA solution Vs EDTA

Standard hard water Burette solution Pipette solution Indicator Endpoint Special Condition

: Disodium salt of EDTA : Standard CaCl2 : Eriochrome Black T : Wine red to steel blue : Added one test tube of pH 10 buffer

S.No 3. 4.

Volume of standard CaCl2 solution(ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of EDTA (ml)

Concordant value = Calculation: Volume of standard CaCl2 solution Normality of standard CaCl2 solution Volume of EDTA solution Normality of EDTA solution V1 N1 V2 N2 = = = = V1N1 / V2 20 ml N ml

ml

=

N

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Ex. No: Date: DETERMINATION OF TOTAL, TEMPORARY, CALCIUM AND MAGNESIUM HARDNESS OF WATER BY EDTA METHOD AIM: To estimate the amount of total, temporary, calcium and magnesium hardness present in the given sample of water by complexometrically. You are being supplied with a standard CaCl2 solution containing ________ g per litre and EDTA as link solution. PRINCIPLE: The hardness of water is due to the presence of dissolved salts of Ca and Mg. These calcium and magnesium ions readily form complexes with EDTA and can be titrated using Eriochrome Black-T as indicator. This complex is unstable and is quickly replaced by more stable Ca/Mg - EDTA complex. Ca2+ / Mg2+ In water EBT Ca2+ / Mg 2+ + + EBT EDTA [EBT Ca 2+ / Mg 2+] (Unstable complex wine red) [EDTA Ca2+ / Mg 2+] + EBT (Blue colour)

(Unstable complex wine red)

More stable Colourless

When Eriochrome Black T is released free, the end point of the titration is marked with the formation of blue coloured solution. Calcium and magnesium bicarbonates cause temporary hardness. On boiling, these substances decompose to form insoluble CaCO3 and Mg (OH)2 and thus temporary hardness is removed according to the following reactions. Ca(HCO3)2 Mg(HCO3)2 CaCO3 + CO2 + H2O Mg(OH)2 + 2CO2

Chlorides and sulphates of Ca/Mg cause permanent hardness to water and cannot be removed by boiling. The sample after boiling and cooling is filtered, and titrated against EDTA to calculate the permanent hardness of water. To estimate the amount of calcium hardness separately, the magnesium ions are precipitated by adding 2N NaOH solution, and then titrated against EDTA using Murexide indicator. Magnesium ions are then evaluated from the difference between total hardness and calcium hardness.

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Titration II: Estimation of total hardness Standardized EDTA Vs Water sample Burette solution Pipette solution Indicator Endpoint Special Condition : : : : : Disodium salt of EDTA Given hard water sample Eriochrome Black T Wine red to steel blue Added one test tube of pH 10 buffer

S.No

Volume of hard water sample (ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of EDTA (ml)

1. 2.

Concordant Value = Calculation: Volume of EDTA solution Normality of EDTA solution Volume of given hard water sample Normality of given hard water sample V1 N1 V2 N2 = = = 20 = V1N1 / V2 ml N ml

ml

= The amount of total hardness of the given water sample

N = N x 50 x 1000

=

ppm

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PROCEDURE: TITRATION I: STANDARDISATION OF EDTA A 20ml pipette is washed with distilled water and rinsed with the given standard CaCl2 solution. Exactly 20 ml of standard CaCl2 solution is pipetted out into a clean conical flask. 10 ml of pH 10 buffer and a pinch of EBT indicator are added into the conical flask. The solution turns wine red in colour. Then this solution is titrated against EDTA till the colour changes from wine red to steel blue. The titration is repeated for concordant values. From the concordant value, the normality of EDTA is calculated.

TITRATION II: ESTIMATION OF TOTAL HARDNESS Exactly 20 ml of given hard water sample whose harness is to be estimated is pipetted out into a clean conical flask. To this, 10ml of pH 10 buffer solution and a pinch of EBT indicator are added into the conical flask. The solution turns wine red in colour. Then this solution is titrated against EDTA till the colour changes from wine red to steel blue. The titration is repeated for concordant values. From the concordant value, the total hardness of water sample is estimated.

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Titration III: Estimation of temporary and permanent Hardness Standardized EDTA Vs Water sample (Boiled, cooled and filtered) Burette solution Pipette solution Indicator Endpoint Special Condition : : : : : Disodium salt of EDTA Hard water sample (Boiled, cooled & filtered) Eriochrome Black T Wine red to steel blue Added one test tube of pH 10 buffer

S.No 1. 2.

Volume of hard water sample (ml)

Burette readings (ml) Initial 0.0 0.0 Final

Volume of EDTA (ml)

Concordant value = Calculation: Volume of EDTA solution Normality of EDTA solution Volume of hard water Normality of hard water . V1 N1 V2 N2 = = = ml N ml = N

ml

= V1N1 / V2 =

The amount of permanent hardness present in the given water sample

=

N x 50 x 1000

= The amount of temporary hardness present in the given water sample

ppm

= Total hardness Permanent hardness = = ppm

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TITRATION III: DETERMINATION OF PERMANENT HARDNESS 100ml of hard water sample is taken in a 250ml beaker and boiled till the volume is reduced to half of the initial volume and allowed to cool. The water is filtered into a 100ml standard measuring flask and the residue over filter paper is washed thoroughly with deionised water and the volume is made to 100ml using deionised water. Exactly 20 ml of the made up water is pipetted out into a clean conical flask. 10 ml of pH 10 buffer and a pinch of EBT indicator are added into the conical flask. The solution turns wine red in colour. Then this solution is titrated against EDTA till the colour changes from wine red to steel blue. From the titre value, the permanent hardness of water sample is calculated.

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Titration IV: Estimation of calcium and magnesium hardness Standardized EDTA Vs Water sample Burette solution Pipette solution Indicator Endpoint Special Condition : : : : : Disodium salt of EDTA Given hard water Murexide Red to Purple Added 1/3rd test tube of 2N NaOH solution. Burette readings (ml) Initial 0.0 0.0 Final Volume of EDTA (ml)

S.No. 1. 2.

Volume of hard water (ml)

Concordant value = Calculation: Volume of EDTA solution Normality of EDTA solution Volume of hard water containing calcium (Ca ) Normality of hard water containing calcium (Ca )2+ 2+

ml

V1 = N1 = V2 = 20

ml N ml

N2 = V1N1 / V2 = =

The amount of calcium hardness of the given water sample

= N x 50 x 1000

= The amount of magnesium (Mg ) hardness of the given water sample = =2+

ppm

Total hardness calcium hardness

=

ppm

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TITRATION IV: DETERMINATION OF CALCIUM HARDNESS Exactly 20ml of the hard water sample is pipetted out into a clean conical flask. To this solution, 5ml of 2N NaOH solution is added followed by a pinch of murexide indicator. It is titrated against standardized EDTA until the colour changes from red to purple. The titration is repeated for concordant values. From the concordant value, the calcium hardness of the water is estimated. The magnesium hardness is calculated from the difference between total hardness and calcium hardness. Equivalent weight of CaCO3 is 50. RESULT: i) The total hardness of the given water sample = __________ ppm. = __________ ppm. = __________ ppm. = __________ ppm.

ii) The temporary hardness of the given water sample iii) The permanent hardness of the given water sample iv) The calcium hardness present in the given water sample

v) The magnesium hardness present in the given water sample = __________ ppm.

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CALCULATION: Volume of water sample taken (V) = ___________ ml = ___________ ml = ___________ ml = ___________ N

Volume of FeSO4 consumed in the sample titration (V1) Volume of FeSO4 consumed in the blank titration Strength of FeSO4 solution (V2) (N)

COD as mg O2 /L =

(V2 V1) x N x 8 x 1000 V

=

COD =

ppm

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Ex. No: Date:

DETRMINATION OF CHEMICAL OXYGEN DEMAND OF A WATER SAMPLEAIM: To estimate the chemical oxygen demand of the given water sample. PRINCIPLE: Chemical oxygen demand (COD) is the parameter which is used to measure the total oxidisable impurities present in the water sample. It is the amount of oxygen required for chemical oxidation of all oxidisable matters (oxidisable impurities) present in the water, with strong chemical oxidant, K2Cr2O7 in acid medium. It is expressed in mg/dm3 or ppm. The water sample is refluxed with known excess of standard K2Cr2O7 solution (oxidizing agent) in sulfuric acid medium in the presence of Ag2SO4 and HgSO4. K2Cr2O7 oxidizes all oxidisable impurities. Ag2SO4 catalyses the oxidation of straight chain and aromatic organic compounds. Halide interferences are avoided by their reaction with HgSO4 by forming soluble complex; otherwise they will precipitate as AgX. After the reaction period, the amount of unreacted K2Cr2O7 is estimated by titrating against standard FeSO4 solution (V1). A blank titration without water sample is also carried out (V2). From the amount of K2Cr2O7 consumed (V2 V1), the COD of the water sample is calculated. The reaction between FeSO4 and K2Cr2O7 can be represented as follows K2Cr2O7 + 4 H2SO4 K2SO4 + Cr2(SO4)3 + 4H2O + 3(O)

[2 FeSO4 + H2SO4 + (O) Fe2(SO4)3 + H2O] x 3 K2Cr2O7 + 6FeSO4 + 7 H2SO4 K2SO4 + Cr2 (SO4)3 + 3Fe2(SO4)3 + 7 H2O

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PROCEDURE: Exactly 20ml of water sample is pipetted out into a clean 250ml conical flask. To this, 20ml of K2Cr2O7 solution and 1test tube of 1:1 H2SO4 are added. This solution is heated for 10 minutes. It is cooled and then ferroin indicator is added. The solution is titrated against FeSO4 solution till the colour changes from greenish blue to reddish brown. A blank titration is carried out without water sample. From the titre values, the COD is calculated.

RESULT: The chemical oxygen demand of the given water sample = ____________ ppm.