TABLE OF CONTENT

CONTENT PAGE

1. Abstract / summary 1

2. Introduction 1-2

3. Aims / objectives 2-3

4. Theory 3-7

5. Apparatus and Materials 7-8

6. Experimental procedure 8-11

7. Result 12-14

8. Sample calculation 14-19

9. Discussion 19-21

10. Conclusion 21

11. Recommendation 21

12. References 22

13. Appendices 23-26

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1.0 ABSTRACT

In this experiment, we have determined the amount of dissolved oxygen (DO) in the

water that was collected in the lake. Through observation, we know that the water

sample contained the oxygen by having colour of orange-brown with precipitate when

added with ManganousSulphate Powder Pillow with Alkali Iodide Azide Reagent

Powder Pillow and it have a colour of yellow when added with Sulfonic Acid Powder.

Both of these proves the existence of oxygen in this water sample.

Besides, there are many factors that affect the level of DO in water systems. The major

source of DO in lake is atmosphere. Waves and tumbling of water will mix the

atmospheric oxygen into the river. DO concentrations in water also increase due to the

oxygen produced by the roots of aquatic plants and algae as a product of

photosynthesis.

The amount of DO can be decreased due to several factors. There are high

temperature and the amount of bacteria and microorganism in a particular water

system. The factor of temperature may result from high turbidity, the return of

industrially used water to the riveror from drought. While, the second factor that can

decrease the amount of DO is bacteria which decompose plant material and animal

waste will consume DO that is present in the water, thus decreasing the quantity

available to support life.

2.0 INTRODUCTION

Comprising over 70% of the Earth’s surface, water is undoubtedly the most

precious natural resource that exists on our planet.  Without the seemingly invaluable

compound comprised of hydrogen and oxygen, life on Earth would be non-existent: it is

essential for everything on our planet to grow and prosper.  Although we as humans

recognize this fact, we disregard it by polluting our rivers, lakes, and oceans.

Subsequently, we are slowly but steadily harming our planet to the point where

organisms are dying at a very alarming rate.  In addition to innocent organisms dying

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off, our drinking water has become greatly affected as is our ability to use water for

recreational purposes.  In order to combat water pollution, we must understand the

problems and become part of the solution.The complexity of water quality as a subject

is reflected in the many types of measurements of water and waste water quality.

The physical, chemical, and biological characteristics are the main criteria to

determine the quality of water. Basically, natural water contains impurities; whereas,

pure distilled water is composed of only oxygen (O2) and hydrogen (H2). The treatment

of waste water requires us to determine the quality of water. The treatment depends

upon the quality of the raw water and the desired quality of treated water.

For this experiment, we are going to study about the dissolved oxygen in water.

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

particularly important in aquatic ecology.Dissolved oxygen is a very important part in

determining the quality of a drinking. A high level of DO in water can be a sign that the

water is of a very good quality. For example, most of mineral water that had undergone

the reverse osmosis process had a very high level of DO.

3.0 OBJECTIVES

1. To learn the specific sampling technique in determining dissolved oxygen

concentration in a sample of water.

2. To determine the concentration of dissolved oxygen in water sample.

3. To identify the factors affecting the concentration of dissolved oxygen in water

sample.

4.0 THEORY

The term Dissolved Oxygen is used to described the amount of oxygen dissolved in

a unit volume of water . Dissolved oxygen (DO) is essential for the maintenance of

healthy lakes and rivers. It is a measure of the ability of water to sustain aquatic life .The

dissolved oxygen content of water is influenced by the sources , raw water temperature

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, treatment and chemical or biological processes taking place in the distribution

system .The presence of oxygen in water is a good sign. Depletion of dissolved water

supplies can encourage the microbial reduction of nitrate to nitrite and sulfate to sulfide.

It can also cause an increase in the concentration of ferrous iron in solution , with

subsequent discoloration at the tap when the water is aerated. Hence ,analysis of

dissolved oxygen is an important step in water pollution control and wastewater

treatment process control . there are various methods available to measure DO. In a

healthy body of water such as lake , river , or stream , the dissolved oxygen is about 8

parts per million. The minimum DO level of 4 to 5 mg/L is desirable for survival of

aquatic life .If that a source of oxygen demanding wastes , such as feed a lot , a paper

mill or a food processing plant , is built besides the river. The facility begins operating

and discharging wastes into the river. This increases the BOD and effects the

concentration of DO in the waters downstream. The wastes serve as the food for certain

aerobic bacteria as it moves downstreams , the concentration of bacteria increases.

Because these bacteria remove oxygen from water , their population increase causes a

decline in the amount of DO. Beyond certain point , most of the wastes break down. The

concentration of DO rises as the river recovers oxygen from the atmosphere and

aquatic plants. Thus , DO test is the basis for BOD test which is an important parameter

to evaluate organic pollution of a waste. It is necessary for all aerobic biological

wastewater treatment processes to control the rate of aeration.

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5.0 APPARATUS AND MATERIAL

Figure1

1-Digital Titrator

3- ‘J’ Delivery Tube

2- Sodium Thiosulfate Titration Cartridge

4. BOD bottle 5. Conical flask

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Figure 3

6. Reagent Compartment 7. Starch Indicator Solution

Manganous Sulfate Powder Pillow

Alkaline Iodide Azide Powder Pillow

Sulfamic Acid Powder Pillow

6.0 PROCEDURES

OXYGEN DISSOLVED: Azide Modification of Winkler Method

1. A water sample was collected in a clean 100 mLBOD bottle.

2. The contents of one Manganous Sulfate Powder Pillow and one Alkaline Iodide

Azide Reagent Powder Pillow were added.

3. The stopper was inserted immediately so that air does not trap in the bottle. The

bottle was inverted for several times to mix. A flocculent precipitate which was

orange brown( O2 present ) or white ( O2 absent ) formed in the bottle. The floc

settled slowly in salt water. Step 4 was preceded when the floc settled.

4. The bottle was inverted for 5 minutes to ensure that the sample and reagents

reaction is complete. When the floc settled and the top half of the solution had

cleared, Step 5 was preceded.

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5. The stopper was removed and the content of one Sulfamic Acid Powder Pillow

was added. The stopper was replaced without trapping air in the bottle. The

sample was inverted several times to mix. The floc dissolved and left a yellow

coloursolution (O2present ).

6. A sample volume and Sodium Thiosulfate Titration Cartridge were selected

corresponding with expected dissolved oxygen ( DO ) concentration.

7. Then a clean delivery tube was inserted into the titration cartridge to the titrator

body. After that, the delivery knob was turned to inject a few drops of titrant. The

counter is resetted to zero and the tip was wiped.

8. A graduate cylinder was used to measure the sample volume and the sample

was transferred to 250 mL Enrienmeyer flask.

9. The delivery tube was placed into the solution and the flask is swirled while the

solution was titrated with sodium thiosulfate to a pale yellow colour.

10.Next, to 1 mL dropper of starch indicator solution were added and the mixture

was swirled.

11.The titration was continued to get a colorless end point. The number of digits

required were recorded.

12.Finally, dissolved oxygen were calculated and being tabulated in a table.

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7.0 RESULT

(I) To determine the amount of dissolved oxygen in the water sample 100

mL BOD bottle

Reagent Observation Conclusion

ManganousSulphate Powder

Pillow + Alkaline Iodide Azide

Powder Pillow

Orang-Brown with

precipitate

Oxygen is present

Sulfonic Acid Powder Yellow colour Oxygen is present

Digit required : 113

Digit multiplier : 0.02

Range dissolver oxygen : 2.26

(II) 20 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 : 22

Digit Multiplier : 0.1

Range dissolver oxygen : 2.2

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8.0 CALCULATIONS

Oxygen Dissolved (Azide Modification Of Winkler)

Using BOD bottle

Sample of calculation:

Digit Multiplier × Digit Required = mg/L Dissolved Oxygen

100 mL (titration cartridge Na2S2O3, 0.2M)

0.02 x 113 = 2.26 mg/L as Dissolved Oxygen

20 mL (titration cartridge Na2S2O3, 0.2M)

0.1 x 22 = 2.2 mg/L as Dissolved Oxygen

9.0 DISCUSSION

This ‘Basic Water Properties 1’ experiment was carried out to:

1. Study the method used to detect the concentration of dissolved oxygen in water

sample.

2. Determine the concentration of dissolved oxygen in water sample.

3. Identify the factors affecting the concentration of dissolved oxygen in water

sample.

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The water sample that we used in this experiment was from Tasik Shah Alam

Seksyen 7. From the experiment, the concentration of dissolved oxygen in water can be

detected using the Hach Dissolved Oxygen Kit. There were 3 types of powder pillow

used to detect the dissolved. The first one was the Manganous Sulfate Powder Pillow.

The Manganous Sulphate Powder Pillow was added into water sample together with the

Alkaline Iodide-Azide Powder Pillow.

What is going on in this step:

Reagent Powder Pillow #1 (Manganous Sulfate) MnSO4

This powder packet contains a powdered chemical called Manganous Sulfate

which reacts with the oxygen present in the water. During the reaction, the

oxygen is bound to the manganese (chemical element Mn), forming a brownish

solid which settles to the bottom of the bottle (MnO2). This process is called

fixing the oxygen. In order for this fixation process to work however, the solution

must be at high pH, so we need another reagent to make this occur...

MnSO4 + O2 MnO2 (brown)

Reagent Powder Pillow #2 (Alkaline Iodide Azide)

If the Manganous Sulfate fixes the oxygen dissolved in the water, why do we need more

chemicals? There are three specific chemicals present in packet #2 which are important

to the fixation of the oxygen.

o LiOH (Lithium Hydroxide) is a base, which means that in water it breaks

up to form the OH- ion, and the Li+ ion. In this reaction, LiOH basically just

functions as a catalyst to activate the binding process. The binding

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process involved with Manganous Sulfate requires a high pH to proceed.

The addition of LiOH does just that.

o KI (Potassium Iodide) is added to function as a dye, and will react with

the sulfamic acid added, as explained below.

o NaN3 (Sodium Azide) is an agent added which will not come into play

until later in the reaction sequence. Because we will not come back to it, a

quick explanation is appropriate. (For a more in-depth explanation, see the

Winkler method titration page.) Basically during the final titration, Sodium

Thiosulfate produces some nitrite (NO2-) which conflicts with the intended

reaction. The addition of Sodium Azide prevents this conflictual reaction

from occuring.

After that the third powder pillow, Sulfamic Acid Powder Pillow was added into

the water sample.

What is this mysterious Sulfamic Acid Powder Pillow?

Reagent Powder Pillow #3 (Sulfamic Acid C6H13O3NS) Upon addition of the

Sulfamic Acid, the MnO2 from above is reduced to Mn2+, and the Iodine from the

Potassium Iodide above is oxidized by the MnO2 from I- to I2. This reaction step

effectively causes the solution to take on a yellow-ish brown color proportional to

the number of I2 molecules present which in turn is proportional to the original

amount of O2 molecules in the water.

MnO2 + 4H+ + 2I- = Mn2+ + I2 + 2H2O (yellow)

We say at this point, that the oxygen is fixed. This means that all of the oxygen from the

original sample which was in solution has now been chemically modified to a form which

won't change when exposed to the air. It is now in a stable form, and can be transported

back to a classroom for analysis if necessary.

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The water sample was titrated with 0.2 M Sodium Thiosulfate to a pale yellow

colour. A dark blue solution was formed when Starch Indicator solution was added. The

titration was continued until a colourless solution was obtained.

From the Digital Titrator, the value obtained was 113. So by multiplying it with the

digital multiplier, we got the concentration of dissolved oxygen in water sample to be

2.26 mg/L. The value of dissolved oxygen was quite high, so this water was suitable for

aquatic organism. This high concentration of dissolved oxygen was mainly due to the

high density of algae surrounding the sewage system. On a bright day, these algae will

carry out photosynthesis and oxygen will be produced. This oxygen will easily dissolve

in the water as the sewage run continuously.

10.0 CONCLUSION

This experiment was a big success. All of the objectives in this experiment had been

achieved. The result was:

1. To study the method used to detect the concentration of dissolved oxygen in

water sample – by using the Hach Dissolve Oxygen Kit.

2. To determine the concentration of dissolved oxygen in water sample – 2.26 mg/L

3. To identify the factors affecting the concentration of dissolved oxygen in water

sample – large population of algae surrounding the lake, the continuous

movement of water in the lake had encourage the oxygen to dissolve into the

water.

11.0 RECOMMENDATIONS

These are the steps to obtain better results of the experiment.

Firstly , if the sample was obtained by a sampling device of some kind , the water

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cannot be simply poured into a BOD bottle, since this would cause aeration of

the sample .

Instead , the sample must be drawn off from a tube located near the bottom of

the sampling device. Place the rubber tube into the bottom of the BOD bottle and

fill the bottle , again allowing the bottle to overflow. For shallow depth use normal

water samplers .

However for depth greater than 150 cm use Kemmerer Sample Bottles.

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12.0 REFERENCES

http://www.kimia.um.edu.my/images/kimia/lab%20manual/level%202/Experiment

%20SCES2441-AnalisisLevel2.pdf

http://www.uic.edu/classes/cemm/cemmlab/Experiment%201-Water%20Content.pdf

http://nitttrc.ac.in/Four%20quadrant/eel/Quadrant%20-%201/exp10_pdf.pdf

http://intro.chem.okstate.edu/1515SP01/Laboratory/Propertiesofwater.pdf

13.0 APPENDIX

PROPOSED NATIONAL WATER QUALITY STANDARDS FOR MALAYSIA

Classes

Parameters Unit I IIA IIB III IV V

Ammoniacal-N mg/L 0.1 0.3 0.3 0.9 2.7 >2.7

BOD mg/L 1 3 3 6 12 >12

COD mg/L 10 25 25 50 100 >100

DO mg/L 7 5-7 5-7 3-5 <3 <1

Ph 6.5-8.5 6-9 6-9 5-9 5-9 -

Colour TCU 15 150 150 - - -

Elec. Cond Μmhos 1000 1000 - - 6000 -

Floatables N N N - - -

Odour N N N - - -

Salinity* % 0.5 1 - - 2 1

Taste N N N - - -

Tot. Diss. Sol.* mg/L 500 1000 - - 4000 -

Tot. Susp. Sol. mg/L 25 50 50 150 300 >300

Temperature ºC - Normal± - Normal± - -

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2 2

Turbidity NTU 5 50 50 - - -

F. Coliform** counts/100

ml

10 - 100 400 5000

(20000)

e

5000

(20000)

e

-

Total Coliform counts/100

ml

100 5000 5000 50000 50000 >50000

Before adding sulfarnic acid, flocculation

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happen

After adding of sulfarnic acid

Digital Titrator with Sodium Thiosulfate

Cartridge

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