water properties

UNIVERSITI TEKNOLOGI MARAFAKULTI KEJURUTERAAN KIMIA

ENGINEERING CHEMISTRY LABORATORY(CHE485)

NAME :MUHAMMAD FAIZ BIN ISMAIL STUDENT NO :2010801434 GROUP :EH 2221B EXPERIMENT :BASIC WATER PROPERTIES ONE DATE PERFORMED: :20th AUGUST 2010 SEMESTER :1 PROGRAMME / CODE :EH222 / CHE485 SUBMIT TO :MADAM RABIATUL ADAWIYAH BINTI ABDUL AZIZ

No. Title Allocated Marks (%) Marks

1 Abstract/Summary 5

2 Introduction 53 Aims 54 Theory 55 Apparatus 56 Methodology/Procedure 107 Results 108 Calculations 109 Discussion 2010 Conclusion 1011 Recommendations 512 Reference 513 Appendix 5

TOTAL MARKS 100

Remarks:

Checked by: Date:

Table of Content

NO Title Pages

1 Abstract/ Summary

2 Introduction

3 Theory

4 Aims/Objectives

5 Apparatus

6 Procedures

7 Results

8 Calculations

9 Discussions

10 Conclusions

11 Recommendations

12 References

13 Appendices

Abstract.

In this experiment, we have determined the amount of dissolved oxygen in the water

sample that we had collected in the pond at the Dataran Cendikia. Through observation, we

know that the water sample contained the oxygen by having colour of orange-brown with

precipitate when added with Manganous Sulphate Powder Pillow with Alkali Iodide Azide

Reagent Powder Pillow and it have a colour of yellow when added with sulfonic acid powder.

Both of this proves the existence of oxygen in this water sample. Then, through a series of

calculation, we measured the amount of the dissolved oxygen in the water sample that is 6.34

mg/L and 7.1 mg/L.

Introduction

Dissolved oxygen (DO) level is refers to the amount of oxygen dissolve in water and

is particularly important in aquatic ecology. Without an appreciable level of DO, many kinds

of aquatic organisms cannot exist in water. A high DO level is needed for the aquatic organ-

ism to live and it makes drinking water taste better than usual. High DO level is important to

every living organism. However, industries reduce to least possible amount of dissolved oxy-

gen in order to reserve it pipeline from corrode.

The level of DO in water is dependent on many physical, chemical, and biochemical

factors—aeration, wind, velocity of water flow, algae, temperature, atmospheric pressure, or-

ganic compounds, salt content, bacteria, and animals. Algae produce oxygen during photo-

synthesis under sunlight. However, this process is really not an efficient means of oxygenat-

ing water because some of the oxygen formed by photosynthesis during the daylight hours is

lost at night when the algae consume oxygen as part of their metabolic processes. When algae

die, the degradation of their biomass also consumes oxygen.

Temperature has a significant impact on the solubility of oxygen in water. Increasing

the temperature will normally decrease the DO concentration in water. It is important to dis-

tinguish between oxygen solubility, which is the maximum DO concentration at equilibrium,

and the actual concentration of DO, which is generally not the equilibrium concentration and

is limited by the rate at which oxygen dissolves. Water saturated with oxygen at 25oC con-

tains 8.4 mg/L.

Therefore, in this experiment, we will determine the amount of dissolve oxygen in

water by using a selected procedure that is Azide Winkler Method. Here, we had checked the

dissolve oxygen in the sample and it must be comply with Malaysian Standard of Water

Quality.

Theory

Winkler test is used in this experiment in order to measure the concentration of

dissolved oxygen (DO) in a water sample. In this method, excess manganese (II) sulphate

will react with the alkali-iodide azide reagent that is an iodide ion (I- ) and potassium

hydroxide ion (OH-) ion in water to form a white precipitate Mn(OH)2. Alkali-iodide azide

also composed of NaN3 that is an alkali azide compound that will eliminated the nitrile

interference that can interfere the reaction of reducing or oxidizing substances in this test.

MnSO4+2KOH Mn(OH)2+K2SO4

If oxygen is present inside the water, the Mn(OH)2 will react further to form an

orange- brown precipitate, manganic oxide (MnO(OH)2) but if the oxygen is not present

inside the water sample, the colour of the white precipitate will remain unchanged. (Ruth F.

Weiner, 2003)pg84)

2Mn(OH)2 + O2 2MnO(OH)

2

Sulfamic acid powder pillow, H3NSO3 is added, which dissolves the manganic oxide

and in together with the potassium iodide, KI added earlier, forms iodine (I2), that had give

the orange colour to the sample:

2Mn(OH)2 + 4H3NSO3 2Mn(SO4)2 + 6 H2O (3)

2Mn(SO4)2 + 4KI 2MnSO4 + 2K2SO4 + 2I2- (4)

Then, by referring table 1, a sample of volume of the solution is taken and poured into

a graduated cylinder.

Range (mg/L

D.O)

Sample volume

(mL)

Titration Cartridge, N

(Na2S2O3)Catalog Number

Digit

Multiplier

1-5 200 0.200 22675-01 0.01

2-10 100 0.200 22675-01 0.02

>10 200 0.200 14401-01 0.10

The quantity of iodine is measured by titrating with sodium thiosulfate (Na2S2O3)

(1)

(2)

until the orange colour from I2 becomes pale yellow as yellow plastic straw.

4 Na2S2O3+ 2I2 2Na2S4O6+ 4NaI (5)

Starch is added near the end of the titration to measure if there is any unreacted iodine,I2 in

the solution as the starch will give a dark blue colour in the presence of I2 and gives a more

obvious colour of endpoint for the test. Then, it is titrated again with sodium thiosulphate

solution until the colour of the solution becomes colourless

The available quantity of MnO(OH)2 formed in the first step is directly proportional to

the dissolved oxygen, and the amount of iodine formed in the second step is directly

proportional to the MnO(OH)4. So, the titration of sodium thiosulphate solution measures a

quantity of iodine directly related to the original dissolved oxygen concentration. Therefore,

by calculating the amounts of sodium thiosulphate used by recording the digits at the body of

the mechanical titrator and multiply its by the digit multiplier given at a sample volume we

had used like in the table 1.

In test 2, we used oxygen powder pillow 1 and 2 to trap the oxygen that gives the

yellow colour of oxygen and then inserted oxygen powder pillow 3 to dissolve any precipitate

and titrate it with sodium thiosulphate as in test 1.

Digits required X Digit Multiplier = ____mg/L Dissolved Oxygen (6)

Here, we obtained the amount of dissolved oxygen in the sample of water that we had

used in this experiment.

Objectives

1. To learn the specific sampling technique in determining

dissolved oxygen concentration in a sample of water.

2. To understand the chemical principle of water for

dissolves oxygen measurement.

3. To determined the dissolved oxygen that contained in a

water sample

Apparatus and Material

Apparatus

I) 300mL BOD Bottle

1. Bottle, with stopper, BOD, 300-mL

2. Clippers, for opening pillows

3. Cylinder, graduated, 250-mL

4. Digital Titrator

5. Flask, Erlenmeyer, 250-mL

6. Delivery tubes

Material

1. Alkaline Iodide-Azide Powder Pillows 50/pkg 107266

2. Manganous Sulfate Powder Pillows 50/pkg 107166

3. Sodium Thiosulfate Titration Cartridge, 0.2000 N each 2267501

4. Starch Indicator Solution

5. Sulfamic Acid Powder Pillows

II) 60mL BOD Bottle

Apparatus

1. Bottle, with stopper, BOD, 60-mL

2. Clippers, for opening pillows

3. Digital Titrator

4. Flask, Erlenmeyer

5. Polypropylene Beaker

6. Delivery tubes

Material

1. Dissolved Oxygen 1 Reagent Powder Pillows



4. Sodium Thiosulfate Titration Cartridge, 0.2000 N each

5. Procedure :-

i) Azide Modification of Winkler Method

a) Using a 300mL BOD Bottle.

1. Water sample is collected in a 300 mL BOD bottle.

2. Sample is allowed to overflow the bottle for 2-3 minutes to ensure that air bubble is

not trapped.

3. Stopper is inserted immediately and inverts several times to mix so that air is not

trapped in the bottle. (Flocculent precipitate formed, H will be orange, brown if

oxygen is present or white if oxygen is absent.)

4. Wait until the flocculent in the solution had settled. The bottle is inverted again for

several times and waits until the flocculent settled again.

5. The stopper is removed and contents of 1 sulfamic acid powder are added into the

solution. The stopper is replaced without trapping air in the bottle and the bottle is

inverted several times for it’s to mix.

6. A sample volume of sodium thiosulphate titration cartridge is selected corresponding

to the expected dissolved oxygen (D.O) concentration from table 1.

7. A clean delivery tube is inserted into the titration cartridge. The cartridge is attached

to the titrator body.

8. Delivery knob is turned to eject a few drops of titrant. The counter is reset to zero and

the tip is wiped.

9. A graduated cylinder is used to measure the sample volume from table 1. The sample

is transferred into a 250mL Erlenmeyer flask.

10. The delivery tube tip is placed into the solution and the flask is swirl while titrating

with sodium thiosulphate to a pale yellow colour.

11. Two 1 mL drop of starch indicator is added into the solution and swirl to mix. (note a

dark blue colour will develop)

12. The titration is continued to a colourless end point and the number of the digits

required is recorded.

13. The value of Dissolved Oxygen in water is calculated by the formula:

Digits required X Digit Multiplier = ____mg/L Dissolved Oxygen

a) Using a 60mL BOD Bottle.

1. A water sample is collected in a clean 60mL glass-stoppered BOD bottle.

(Note: Allowed the sample to overflow the bottle for 2-3minutes to ensure air bubbles

are not trapped)

(Note: If samples cannot be analysed immediately see sampling and storage following

these steps.

(Note: This procedure is followed when using the 60mL glass-stoppered BOD bottle

supplied with DREL Portable laboratories.

2. The contents of one dissolved oxygen 1 reagent powder pillow and one dissolved

oxygen 2 reagent powder pillows is added.

3. The stopper is inserted immediately so air is not trapped in the bottle. The bottle is

inverted several times in order for it to mix.

4. Wait until the flocculent in the solution has settled and the top half of the solution is

clear. The bottle is inverted again for several times and waits until the flocculent has

settled.

(Note: Results are not affected if the flocculent does not settle or if some of the

reagent powder does not dissolve.)

5. The stopper is removed and the contents of one dissolved oxygen 3 powder pillow are

added. The stopper is replaced without trapping air in the bottle and it is inverted for

several times to mix.

(Note: The flocculent will dissolve and leave the yellow colour of Oxygen if present)

6. 20mL of the prepared sample is accurately measured and transfer into the 250mL

Erlenmeyer flask.

7. A clean straight-stem delivery tube is attached to a 0.2000N sodium thiosulphate

titration cartridge. The cartridge is twisted onto the titrator body.

8. The delivery tube is flushed by turning the delivery knob to eject a few drops of

titrant. The counter is reset to zero and the tip is wiped.

9. The prepared solution is titrated with 0.2000N Sodium Thiosulphate until the sample

changes from yellow to colourless. The number of digits is recorded.

10. The amount of dissolved oxygen in the water sample is calculated

Digits required X Digit Multiplier = _____mg/L Dissolved Oxygen

Result:-

(I) To Determine the Amount of Dissolved Oxygen in the Water Sample .

300 mL BOD bottle.

Reagent Observation Conclusion

Manganous Sulphate Powder

Pillow + Alkaline Iodide Azide

Powder Pillow

Orange-Brown with Precipitate Oxygen is Present

Sulfonic Acid Powder Yellow Colour Oxygen is Present

Digit Required : 317

Digit Multiplier 0.02

Range (mg/L) Dissolve Oxygen = Digit Required X Digit Multiplier

= 317 X 0.02

= 6.34 mg/L (In Range)

(II) 60 mL BOD bottle.

Reagent Observation Conclusion

(Dissolved Oxygen 1 + Dissolved Oxygen 2 + Dissolved

Oxygen 3 ) Reagent Powder Pillow

Orange-Brown Oxygen is Present

Digit Required : 71



= 71 X 0.1


Sample Calculation:

Digits required X Digit Multiplier = _____mg/L Dissolved Oxygen

(I) To Determine the Amount of Dissolved Oxygen in the Water Sample .

300 mL BOD bottle.

Digit Required : 317



= 317 X 0.02


(III) 60 mL BOD bottle.

Digit Required : 71



= 71 X 0.1


Discussion

In this experiment, we want to determined the amount of dissolved oxygen in the

water sample that we had taken in the pond at Dataran Cendikia. In this experiment, we used

Winkler Test and the main solution here is azide, so the method is known as Azide-Winkler

Test and the solution used is known as alkali-iodide azide solution. This is due to the role of

azide or NaN3 in becoming the inhibitor for the interference of nitrogen ion from interfering

the oxidation and reduction process that occurred in this experiment by the oxygen and

iodine. The solution used is according to the situation we are facing.

First of all, we had inserted the water sample until it overflow. This is to ensure there

is no air bubbles trapped and in order to get the accurate reading of the oxygen level that is

inside the water sample. If not, the reading will be altered as the air bubbles trapped also have

oxygen inside it. So it will not just be only the water sample oxygen reading.

We added manganeous sulphate and alkaline iodide azide, here we know that its

reacted by observing the changes that a white precipitate Mn(OH)2 had formed and we can

understand it by equation one

MnSO4+2KOH Mn(OH)2+K2SO4 (1)

The white precipitate that is Mn(OH)2 then had turned into an orange-brown

precipitate that is (MnO(OH)2) due to the present of oxygen inside the water. (Ruth F.

Weiner, 2003)pg84) Here, we inverted the bottle a few times in order to makes it mix with

each other and react.

2Mn(OH)2 + O2 2MnO(OH)2 (2)

Then, the sulfamic powder pillow, H3NSO3 is added, and its dissolves the manganese

oxide in together with the, KI added earlier that makes the precipitate loses and forms iodine

(I2), that had give the orange colour to the water sample without precipitate due to the oxygen

present.

By referring to the table one given, we had selected a 100mL of sample volume, then

transferred into Erlenmeyer flask by a graduated cylinder and a 0.200 titration cartridge with

a catalog number 22675-1 and digit multiplier of 0.02. The digital titrator need to be adjusted

first after inserting the cartridge. First of all, a few drops of titrant must be ejected from the

digital titrator in order to get rid of the air bubble because we want an accurate value of

dissolve oxygen in the water sample and if we had air bubble inside the cartridge of the

digital titrator this will make us having a systematic error.

The delivery tube must be placed inside the solution of sample in order to prevent any

air from the environment entering the sample while conducting this experiment. The flask is

swirl in order to mix the solution faster until it turn to pale yellow.

4 Na2S2O3+ 2I2 2Na2S4O6+ 4NaI (5)

Then, we add two 1mL droppers of starch indicator solution and swirl and here we

had observed that the solution had turned into a dark blue colour. This is due to the iodine

exist inside the solution. By the equation, we know that the available quantity of MnO(OH)2

formed in the first step is directly proportional to the dissolved oxygen, and the amount of

iodine formed in the second step is directly proportional to the MnO(OH)4. So, the titration of

sodium thiosulphate solution measures a quantity of iodine directly related to the original

dissolved oxygen concentration.

We had to continued the titration until the colour become colourless because the

amount of sodium thiosulphate used is equal to amount of Iodine inside the solution and more

importantly it is equal to the amount of dissolve oxygen inside the solution. This is the reason

why we need to titrate until the solution becomes colourless.

Therefore, by calculating the amounts of sodium thiosulphate used by recording the

digits at the body of the mechanical titrator and multiply its by the digit multiplier given in

table 1, we will know the amount of oxygen dissolved inside the sample solution.

In the second test, we used the 60mL of BOD bottle in order to determined the

dissolved oxygen in the water sample. The step is the same as the first test, but we had

inserted oxygen powder pillow 1 and 2 first into the sample in order to trap all the available

oxygen inside the water sample. The yellow colour of the solution that is allowed to settle

before adding oxygen powder pillow 3 is the oxygen colour that had been trapped by the

oxygen powder pillow 1 and 2. The third powder pillow is inserted to eliminate any particles

before the titration process.

Then, the titration is done like the first test by using sodium thiosulphate cartridge

with the digital titrator until the colour of the solution turn to colourless. By calculating the

amounts of sodium thiosulphate used by recording the digits at the body of the digital titrator

and multiply its by the digit multiplier given in table 1 that we had used, we will know the

amount of oxygen dissolved inside the sample solution.

Conclusion

By this experiment, we had known that there is three sampling technique in

determining dissolved oxygen concentration in a sample of water. The three techniques are

Azide-Winkler Method, Probe and Meter Method, and QA/QC considerations. However in

this experiment, we used Azide-Winkler Method as it is the most accurate method in

determining oxygen dissolved content in sample of water. Azide-Winkler Method is a

titration method by using sodium thiosulphate and the amount of oxygen dissolved is equal to

the amount of sodium thiosulphate used in this experiment.

After conducting this experiment, we measured that the oxygen colour is orange-

brown and the dissolved oxygen in 300mL BOD bottle that we used in the first test contain

6.34 mg/L oxygen dissolved and in the second test, we have 7.1 mg/L oxygen dissolved. We

had conduct this experiment with the same water sample and the first test is to measure the

dissolve oxygen accurately and the second test is to measure the oxygen content inside the

water sample roughly so the first test that we had done don’t have an exceeding value.

We also had understand the chemical principle of water for dissolved oxygen

measurement by the understanding the reaction between the reactant used and the water.

Overall, there is it is basically a redox reaction which uses the dissolved oxygen as a reagent.

The alkali azide, NaN3 used is to makes the nitrogen ion don’t interfere the reaction reduction

and oxidation reaction that proceed in this experiment. If alkali azide not exist, the nitrogen

ion contain inside water sample will interfere the reaction and this phenomenon is called as

interference.

Recommendation

We must swirl the bottle after mixing each drop of the sodium thiosulphate solution

during the titration process so that the reactant react faster. Place a white paper or other white

background as a base to the bottle so that we can observed the colour change better and this is

a vital step as the change of the yellow colour to colourless is the end point of this experiment

and we will know the dissolve oxygen concentration by calculating the sodium thiosulphate

solution that we had used in the titration process. As if we had added it excessively, we would

not get an accurate result.

If the water sample is collected on a cold day, it is very important to do the dissolved

oxygen test in an instant after collecting the water sample as the oxygen inside the water will

lowered when the day become warmth. First, we must put the first two chemicals that is

Dissolved Oxygen powder pillows one and two in order to entrapped all the oxygen inside

the water sample and then we can take it back to warmth to finish the test as the oxygen

dissolved inside the water sample will be unchanged as it is trapped inside the water sample

by the dissolved oxygen powder pillow.

References

Bibliography

1. Ruth F. Weiner, R. A. (2003). Environmental engineering. United States Of America: Elsevier Science (USA).

2. http://pubs.acs.org/doi/abs/10.1021/i560097a014

3. http://en.wikipedia.org/wiki/Iodine

4. http://en.wikipedia.org/wiki/Iodine_clock_reaction

5. http://en.wikipedia.org/wiki/Manganese

6. v=onepage&q=MnSO4%20reaction%20in%20winkler&f=false

7. http://en.wikipedia.org/wiki/Sulfamic_acid

8. http://www.lamotte.com/pages/common/pdf/instruct/7414.pdf

Appendices

water properties

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