1.0 DISCUSSION

Note: Level A is located at the bottom of the tank, whereas level C is located at the top of the tank

Part 1

In this part of the experiment from the table (by comparison), it can be concluded that when the pH value increases, the amount of dissolved oxygen decreases, and the conductivity increases. The mixing has an initial pH value of 7.00 as it contains only pure water. As shown in graph 1, 2 and 3, the pH value of the tank shows a constant. Initially, HCL is added into the mixing tank through dosing tank, the pH value has shown a significant drop in the graph. (pH value for acidic solution ranges from 0 to 6.9) After some time, when HCL and pure water is perfectly mixed, it starts to become constant again, but at a lower pH value.

After that, the mixing tank is prepared for the insertion of NaOH solution, which is also added into the mixing tank through dosing tank. As shown from the graph, the pH value has increased rapidly at point of adding NaOH solution. After some time when the solution is mixed well, the pH value in the graph becomes constant.

After the insertion of alkali solution, the tank is left mixing for some time. It is shown in the graph that the adding of acid and solution will result in water and salt solution, which in order words, the solution is neutralized, since in the graph it shows the solution returns back to neutral state after mixing.

The experiment is carried out at 3 different water level, A, B, and C, it all shows the same phenomena in which the final solution returns back to pH 7. However, according to the data obtained, the dissolved oxygen after acid is added to pure water increases, and slightly decreases after alkali solution is added again. This shows that the mixture has more dissolved oxygen when there are free electron ions in the mixture. Besides, the data shows the conductivity is lower at pure water, and increased when acid solution is added, and slightly decreased when alkali solution is added. This may due to the presence of free electron ion for electricity conduction.

Part 2

In the second part of the experiment, air is mixed with water. The pH value of water has slightly increased, which may due to the presence of different components of air that caused the water to become slightly alkalic. Besides, the dissolved oxygen in mixture and conductivity of mixture has a very small and negligible change, which means the mixing of air into water does not cause any changes to the dissolved oxygen in mixture and conductivity.

Part 3

In the final part of the experiment, nitrogen is mixed with water. The pH value has a slight increment as the presence of nitrogen in the mixture has made it more alkalic. Also, the dissolved oxygen in water has decreased due to the presence of nitrogen. Finally, the conductivity of the mixture has a negligible change, which means the presence of nitrogen has not done any changes to the conductivity of the mixture.

Errors

There were some errors that were faced throughout this experiment.

1. There was a leakage occurred during this experiment which could affect the result of this experiment.

2. Instrumental error whereby the measurement fluctuates and are not properly calibrated and this may have caused a minor disruption in the overall results of the experiment.

3. Human error during the monitoring of the switch – closing of switch and measurement of the pH, conductivity and DO values at certain time interval would result in error inaccurate reaction time.

4. There are contaminants that are already present in the city water. This interrupts the values of pH measured.

5. The instrument is less sensitive. This thus affects the reading.6. In the experiment, the printer makes smudges on the graph, hence this makes it difficult to

read.

Modifications

1. Check the piping and valves involved in this experiment to ensure there is no leakage or damage that could affect the result of this experiment.

2. An automatic measuring device is installed to the system whereby it computerizes and measures the required values accurately and efficiently.

3. 3 readings are taken down and the average of it is calculated. The instruments are made sure to work properly beforehand.

4. Check the pH of water at the initial state of the experiment, and make sure it is at a neutral state.

5. The instrument needs to be calibrated regularly by the lab technician from time to time to improve its accuracy and sensitivity.

6. Replace the printer ink with quick drying ones, do not use water ink printer. This will be better; hence the reading on the graph can be improved.

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2.0 CONCLUSION

In the conclusion, the objective of this experiment which is to conduct calibration check on the pH electrode and its amplifier system achieved and also based on the acquired result from part A, conductivity decreases with increase in the level. However, for the initial reading for the conductivity, it shows that conductivity increases with the increase in the level. This shows that water at level A has is more conductive, followed by level C for acid and alkali. For initial, the water level at C is more conductive compared to A. It happens for both Acids and Bases. On other hand, this experiment is to determine the relationship between the height of water in the mixing tank and pH, dissolved oxygen (DO) and conductivity, as well as the effect of presence of nitrogen and air on the dissolved oxygen (DO) in the city water.

PART I: Experiment for pH, Dissolved Oxygen (DO) and Conductivity at varying levels so in this part of the experiment from the table (by comparison), it can be concluded that when the pH value increases because a lower level of liquid is easier to achieve change in pH per unit time rather than in a higher level liquid. In this part of the experiment from the table (by comparison), it can be concluded that when the pH value increases, the amount of dissolved oxygen decreases, and the conductivity increases.

PART II: Experiment for Dissolved Oxygen Measurement In this part of the experiment, city water is used. For the bubbling system that uses air. It can be seen from both the table of Dissolved Oxygen vs. time that there is an increase in oxygen content in the city water. This can be explained by a simple explanatory concept that as time increases.

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3.0 REFERENCES

1. Conductivity in theory and practice Yokogawa Elecrofact BV edition TE 12D7AO-E

2. PH202G pH transmitter User/s manual, Yokogawa Europe B.V IM 12B6C3-E-H

3. SC402G Conductivity and resistivity converter Yokogawa Europe BV IM12D7C3-E-H

4. Instruction Manual for DO30/FD30/PB30 Sensors and Fittings for Dissolved Oxygen, Yokogawa

Europe BV IM12J6K4-E/D/F-H

5. Seborg D. E., Edgar T.F., Mellichamp D.A., Doyle III F.J. (n.d.) Process Dynamics and Control, 3rd edition, Wiley, 2011

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