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Universiti Teknologi PETRONAS

CCBBBB 22009933

PPrroocceessss IInnssttrruummeennttaattiioonn

LABORATORY REPORT

EXPERIMENT 3

pH, DISSOLVED OXYGEN AND CONDUCTIVITY MEASUREMENT

KHADIJATUL-AKMAL BINTI AHMADHAMIZI 0011954

KHUONG MINH CAM TU 0012963

LAILA SAKINAH BINTI JUSOH 0011961

LAURA TIONG SIEW ZIN 0011963

Date of experiment: 14-10-2010

Date of submission: 21-10-2010



Objectives

1. To conduct calibration check on the pH electrode and its amplifier system2. To conduct calibration check on the conductivity electrode and its amplifier

system3. Measurement study of the effect of acid-base titration on Ph

4. Measurement study of the effect of acid-base titration on conductivity5. To conduct calibration check on the dissolved oxygen electrode and its

amplifier system6. Measurement study of the various gas bubbles on dissolved oxygen

Abstract

In this experiment, the objectives are to investigate the effect of acid -base

titration on pH and conductivity and also the effect of various gas bubbles on

dissolved onxygen (DO) value. For the first part, city water is filled in the tank until

level A and then acid is added in followed by alkali. The readings of pH, DO and

conductivity is taken before and after adding in acid and also after adding in alkali.

Then, the tank is cleaned and the same procedure is repeated but the water is filled

until level A. The readings are taken and compared with readings when water is at

level A.

In the second part, the tank is filled with city water until level C. The initial

readings of pH, DO and conductivity are recorded. Then, air is bubbled in for 10

minutes. The final readings are recorded. The same procedure is repeated but

replacing the air by nitrogen gas. The initial and final readings are onserved and

recorded.

From the data and graphs obtained, we can see the changes of pH, DO and

conductivity of the solution when acid and alkali is added in and also when oxygen

and nitrogen is bubbled in. From the results, we can see that as pH value decreases,

the conductivity increases. As the amount of water increases, the conductivity

decreases. And last but not least, as the amount of dissolved oxygen in the water

incerases, the conductivity will also increase as the oxygen creates an acidic

medium.





Procedure

Experiment 1: Titration of acid HCl and Base NaOH

1. It is ensured that the mixing tank, dosing tank and water tank are clean and do

not have any contamination.

2. A mixing tank is filled with city water to about 80% full. It is ensured that themanual valve for water tank MV-H2O is fully open.

3. Acid HCl solution and base NaOH solution is put into the dosing tank.

4. Valve MV-EC (manual valve for electrode chamber) is opened to enablesolution to flow back into the mixing tank.

5. MV-EC is shut off and MV-DM is opened (manual valve for demineralizer). Thecirculating pump is switched ON. The solution inside the mixing tank would be

drained after going through the demineralizer. The circulating pump is shutwhen draining completed.

6. MV-DM is shut off and MV-EC is opened to 45%. ater pump is switched on.ater will flow into the mixing tank.

. The circulating pump is switched on when water level is approximat ely 3 cmdeep.

8. The water pump is switched off when water reaches level A.

9. The dosing volume dial for acid and alkali dosing pumps are checked. It is

made sure that the dial pointer is at 0% of the scale and fre uency is at IIposition. The reading of pH, conductivity is taken and it is recorded into tablewhen reading is stabilized.

10. Switch on acid dosing pump and start the stopwatch. Acid HCl solution will bedosed into the mixing tank. Start recording by pressing REC on recorder. Noticethere should be a light indicator to indicate the start of recording.

11. The pH value and conductivity value shall change with the addition of acid HCl.

12. Acid dosing pump is switched off to stop dosing when time is 4 minutes. Thereading is allowed to stabilized for anothe r 4 minutes.

13. At 8.00 minutes alkali dosing pump is switched on to start dosing NaOH.

14. The base is let to be dosed into mixing tank. pH of the system should be gettinghigher due to reaction between acid and alkali. You should be able to notice thechange of pH and conductivity values due to the process of naturalization.



15. REC button on the recorder is pressed to stop recording. The button FEED inthe Recorder is pressed for 10 seconds. This will create an extension so thatthe chart of that experiment¶s data located can be located.

16. The experiment graph is collected on the chart paper.

1 . The experiment graph is repeated on the chart paper.

18. Steps 1 to 1 are repeated for water level C.

19. The re uired data into DATA and RESULTS section are recorded andcalculated.

Experiment 2: Dissolved Oxygen Measurement

1. ater pump is switched on to allow water to be pumped into mixing tank. Thecirculating pump is switched on when water reach level A.

2. The water pump is stopped when water fills the mixing tank with city until levelC.

3. It is made sure that there is pneumatic supply at 15 psi. The pneumatic air regulator is checked to start recording. The stop watch is started.

4. The manual valve MV-AIR is switched on. REC button on the recorder ispressed to start recording. The stopwatch is started.

5. The pneumatic supply is switched off when time is 10:00.

6. REC button is pressed to stop recording. FEED button is pressed to extantsome length of chart paper so that the chart can be collected from the recorder.

. The circulating pump is stopped and water from the electrode chamber isallowed to drain back to the mixing tank.

8. MV-EC is shut off and MV-DM is opened. The circulating pump is started. ater inside mixing tank to draw into the drain.

9. Circulating pump is turned off when all water inside the mixing tank been drainout.

10. Steps 1 to 9 are repeated for experiment by using nitrogen air bubbling.However the manual valve MV-N2 is opened at step 4 and not MV-AIR.



Results:

Experiment 1

Water at Level A

pH DO Conductivity

Initial reading 11.91 .98 93.0 (mS/cm)

After acid 5.24 .85 9 80 (S/cm)

After alkali 11.40 .80 3 0 (S/cm)

Water at Level C

pH DO Conductivity

Initial reading 10.16 .80 204 (mS/cm)

After acid 4.86 .89 6260 (S/cm)

After alkali 9.11 .88 2130 (S/cm)

Experiment 2

Air

pH DO Conductivity(S/cm)

Initial reading 9. 3 .91 153.8

After air 10.14 8.13 15 .

Nitrogen

pH DO Conductivity

(S/cm)

Initial reading 10.95 .88 96.3

After air 11.03 0.20 93.3



Discussion:

The experiment is conducted to study the relationship between pH, dissolved

oxygen and conductivity.

Conductivity is a solution¶s ability to transmit and electric charge. It is

established according to the number of ions in the solution A high concentration of

ions will correspond to high conductivity (assuming there is no reaction between the

ions present). The higher the number of ions is, the higher the conductivity degree

will be. If ions react/bind to form compounds or molecules, conductivity will decre ase.

If greater dissociation occurs as a result of the presence of certain ions, conductivity

will increase. For example, two solutions having the same number of ions, the

presence of the hydroxide anion in Solution B decreases the conductivity of the

solution because of its ability to form compounds with other ions. The density and

mobility of the ions, as well as the viscosity of the solution (ability to flow) will also

affect the conductivity. More mobile ions will have higher conductivity, but a highly

viscous solution will make it more difficult for the ions to move (lowering the

conductivity).

Ph value is the measurement of amount of H ions present in the solution. The

pH scale ranges from 0-14. These are standardized values used to measure theacidity or alkalinity (how basic) a particular substances is. A pH of seven indicates

that the substance/solution is neutral. Any pH reading below denotes the solution is

acidic, while readings above denote the solution is basic. Essentially, pH is a

measurement of the concentration of hydronium ions (H ) present and is given by

the e uation:

pH -log [H ]

For this experiment, the objective is to conduct calibration check on the pH

electrode, conductivity electrode and its amplifier system and to study of the effect of

acid-base titration on pH and conductivity. For both parts, we insert water, following

by acid and alkali both with interval of 4 minutes. For part 1(a), we inserted water

until level A whereas for part 1(b), we inserted water until level C which is higher than

level A. The volume of water in part b is larger than that of part a. The amount of

alkali and acid added is same for both experiments. Thus, the result is collected from



the graph obtained from the experiment. The value of dissol ved oxygen remains

almost constant in both parts of the experiment. Thus, the major concern of this

experiment is the relationship between concentration of acid -base in the solution and

its conductivity.

The pH scale corresponds to the concentration of (H3O¥

) hydronium ions in a

solution. In fact, if we take the exponent of the H3O¥

concentration and remove the

negative sign, you have the pH of a solution. For example, in pure water the

concentration of hydronium ions is 1 x 10-

¦

M. Thus, the pH of a solution of pure

water is . The solution becomes acidic because it contains more H 3O¥

ions but

when pH value increase, it means that it contains less H 3O¥

ions.

From the result, we can see that there is significant change in conductivity

when the acid and alkali are added. When we add in acid, the pH value will

decrease but conductivity will increase. From this, it can be explain that acid medium

favour the transmission of electric charge. This is because when a medium is more

acid, that means there are more hydronium ions present in the medium. Hydronium

ions are good conductor of electric charge. However, after the alkali has been added

in, the conductivity of the solution decreases because most of the electric charge

transmit agent are being neutralize by the alkali. There is less hydronium ion in morealkali solution. Thus, the conductivity of solution is higher when acid is added as

compared to alkali.

Next, we will look at the effect of water volume to the conductivity of the

solution with condition the amount of acid and alkali added are same in both

experiment. The water volume added in part 1b is more than that of part 1a. From

the result, we can see that the conductivity of the part 1a solution is higher than that

of part 1b. The amount of water and the concentration of acid-base affect the pH

value and their conductivity. When the water volume is increased, the solution tends

to become more diluted as the amount of acid alkali added is the same. This means

that the distance between ions are increased and it will take longer time for the

electric charges to be transmitted in larger medium which has same hydronium ions

as in the smaller medium. Thus, when the amount of acid alkali added is made



constant, the conductivity of the solution will decreases, when the water volume

added is increased.

For the second part of the experiment, the objective is to study the effect of

dissolved oxygen in the composition of water when two different gases are inserted

into the water. For part 2(a), we inserted air which contained 8% nitrogen gases,

21% oxygen gases and1 % of inert gases whereas for part 2(b), we inserted a pure

nitrogen gas into the dosing tank containing water. Thus, the result is collected from

the graph obtained from the experiment . The major concern is the amount of

dissolved oxygen in the solution.

From part 2b, we can see that there is significant change in the amount of

dissolved oxygen, from .88 to 0.2, this lead us to the conclusion that N 2 dissolves in

water much more than O2, and N2 took place of O2 in the solution and decreased the

amount of O2 in the solution. This is suitable with the fact is that the solubility of N 2

and O2 in the water are 0.0138 and 0.0089 g/kg, respectively.

However, in part 2a, although the amount of N2 in air is uite high ( 9%) but

the amount of dissolved O2 was increased (from .91 to 8.13) but not decreased as

in part 2b. This may be due to the ³affinity phenomena´. Oxygen existed in the

solution attracted more oxygen from air but not nitrogen, leading the amount of

oxygen dissolved increased.

The conductivity of the water in part 2a is higher as compared in part 2b. This

is because the dissolved oxygen contained in part 2a is higher. More dissolved

oxygen will lead to more acidic condition as there is more H ion presented in the

water. Acidic medium favours conductivity.



Error Analysis:

During the experiment, there are errors which occur and influence the accuracy of the

result obtained.

1) Parallax error may occur when water is added in to the tank to a certain

desired level. As the tank is located uite high from the reach of student,

chances of parallax error is very high when student could not read the level of

the water directly proportional to the point made on the surface of the ta nk.

Proper scale is not given too.

y It is suggested to provide ladder for the student to ease the water level

measurement taking. Proper scale should be provided too in order to

make sure that the water level desired is correct.

2) The water volume added is not exactly the same as the theoretical volume

because it is hard to control the flow rate of the water and make sure that it is

exactly the same volume as what is re uired.

y E uipment like digital water flow rate controller could be used to make

sure that the volume obtained is correct.

3) The water tank is not cleaned properly at the end of each experiment. This

will affect the result obtained because if the tank is not cleaned thoroughly,

there are still some contaminated li uid present in the tank. When clean water

is being added in, it will be contaminated too when the water is blended with

the previous contaminated li uid which still left in the tank.

y The tank should be designed in a way that it can be taken out for

cleaning purpose and installed back again. By this way, the chance of

new water added being contaminated can be lessened.



Conclusion:

pH value of the solution will affect the conductivity of the solution. The lower

the pH value, the higher the conductivity. When amount of water in creases with the

condition the amount of acid added constant, the conductivity will decreases due to

the increases of electric charge transmission distance. Besides, when the dissolved

oxygen in water increases, it will create an acidic medium which will increase the

conductivity. In conclusion, the objectives of the experiment are achieved.



Appendix

Figure 1: Graph for Experiment 1, water at level A

Figure 2: Graph for Experiment 1, water at level C



Figure 3: Graph for Experiment 2, with air

Graph for Experiment 2, with nitrogen gas

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