discussion experiment 5

5.0 RESULTS

EXPERIMENT 1 : Ph VALUE, DISSOLVED OXYGEN (DO) AND CONDUCTIVITY AT DIFFERENT LEVEL DIFFERENT LEVEL

pH DO Conductivity (μs /cm)

Level AInitial 11.98 1.2 83.8Acid 7 1.68 2850

Alkali 7.67 1.53 1905Level B

Initial 10.48 1.9 188.5Acid 6.95 1.9 2950

Alkali 7.95 1.82 1525Level C

Initial 10.58 1.97 134.5Acid 6.96 2.07 2840

Alkali 7.81 2.02 1325

EXPERIMENT 2: Ph VALUE, DISSOLVED OXYGEN (DO) AND CONDUCTIVITY OF AIR AND OXYGEN AT LEVEL A

Time (minutes) pH DO Conductivity (μs /cm)

Air0 (Initial) 11.97 2.27 84.85 (Final) 12.19 2.35 85.4

Nitrogen0 (Initial) 11.86 2.37 83.65 (Final) 12.62 1.05 83.4


Graph 1 : Graph Of Dissolved Oxygen, DO vs pH at varying level

Graph 2 : Graph Of Conductivity vs pH at varying level

6 7 8 9 10 11 12 130

0.5

1

1.5

2

2.5

f(x) = − 0.0252560488934781 x + 2.23341361314989R² = 0.914268969943908f(x) = 0.0061625834516509 x + 1.82119787733237R² = 0.0589297042564098f(x) = − 0.0892906853103452 x + 2.26319892117357R² = 0.96576094460045

Graph of Disolved Oxygen,DO vs pH at varying level

level ALinear (level A)level BLinear (level B)level CLinear (level C)

pH

Diss

olve

d ox

gen

6 7 8 9 10 11 12 130

500

1000

1500

2000

2500

3000

3500

f(x) = − 668.812965702007 x + 7084.63622684862R² = 0.87172574017704

f(x) = − 732.785548137631 x + 7753.86573724436R² = 0.932056811503597f(x) = − 507.88351047566 x + 6124.63185139212R² = 0.953034795346594

Graph of Conductivity vs pH at Varying Level

level ALinear (level A)level BLinear (level B)level CLinear (level C)

pH

Cond

uctiv

ity


Graph 3 : Graph Of Dissolved Oxygen for Air and Nitrogen, DO vs Time at level A

Graph 4 : Graph Of Dissolved Oxygen for Air and Nitrogen, DO vs pH at level A

0 1 2 3 4 5 60

0.5

1

1.5

2

2.5

f(x) = − 0.264 x + 2.37R² = 1f(x) = 0.016 x + 2.27R² = 1

Graph of Dissolved Oxygen vs Time

AIRLinear (AIR)NitrogenLinear (Nitrogen)

Time

Diss

olve

d O

xyge

n

11.8 11.9 12 12.1 12.2 12.3 12.4 12.5 12.6 12.70

0.5

1

1.5

2

2.5

f(x) = − 1.73684210526316 x + 22.9689473684211R² = 1

f(x) = 0.363636363636366 x − 2.0827272727273R² = 1

Graph of Dissolved Oxygen, DO vs pH

AIRLinear (AIR)NitrogenLinear (Nitrogen)

Time

Diss

olve

d O

xyge

n

DISCUSSION


The objective of Experiment 1 is to determine the relationship between the height of water in the mixing tank and pH, dissolved oxygen (DO) and conductivity. In this experiment, there is a city water tank which acts as a medium for chemical reaction. It will then be dosed into a mixing tank together with acid or alkali which is pumped in by individual dosing pumps (controlled by switch). Level A is located at the bottom of the tank, Level B is located between Level A and Level C whereas level C is located at the top of the tank.

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 initial pH value of level A city water is higher than the initial pH value of level B and C city water. When the acid is added, the pH value of level A, B and C city water drop because lower pH value (<7) of a solution specifies acidity. When the alkali is added, the pH value of A, B and C city water rise because higher pH value (>7) of a solution indicates alkaline. pH value of 7 indicates neutral. Level A has the highest pH changes compared with level B and level C. This is due to a lower level of city water indicates the lesser volume of city water and hence, the change in pH value per unit time in the city is higher. Finally, it all shows the same phenomena in which the final solution returns back to pH 7.

The conductivity of city water varies with the pH value of city water. 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. Moreover, 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 probably due to the existence of free electron ion for electricity conduction.

Lastly, we have plotted two graphs using the data tabulated which is pH vs Dissolved Oxygen and pH vs Conductivity. From the observation of both graphs, the trend of lines is similar and the results achieved are corresponding to the theories.


The objective of Experiment 2 is to study the effect of presence of nitrogen and air on pH, dissolved oxygen (DO) and conductivity in the city water. In this part of the experiment, city water is used and the level that is used for both gases is level A. For the bubbling system that uses air, it can be observed from both the table and graph of Dissolved Oxygen vs. time that there is an increase in oxygen content in the city water. This can be clarified by a simple explanatory concept that when time increases, more oxygen molecules is given the opportunity to be dissolved into the water until an appropriate equilibrium is achieved.

When a bubbling system of nitrogen is used, it can be seen from both the table and graph of Dissolved Oxygen vs. time that there is a decrease in oxygen content in the city water. Again, this can be explained by a simple explanatory concept that the more nitrogen molecules are added into the city water, the lesser the oxygen content will be. So, it can be said that nitrogen bubbling will act as inert in the city water.

ERRORSThere 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. The instrument is less sensitive. This could affects the reading for this experiment.5. There are contaminants that are already exist in the city water. This interrupts the

values of pH measured. 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. The instrument needs to be calibrated regularly by the lab technician from time to

time to improve its accuracy and sensitivity.5. Check the pH of water at the initial state of the experiment, and make sure it is at a

neutral state.

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.

APPENDICES

Graph 1: pH value, dissolved oxygen and conductivity in Level A

Graph 2: pH value, dissolved oxygen and conductivity in Level B

Graph 3: pH value, dissolved oxygen and conductivity in Level C

Graph 4: pH value, dissolved oxygen and conductivity when air is mixed with water

Graph 5: pH value, dissolved oxygen and conductivity when nitrogen is mixed with water

discussion experiment 5

Documents

ph vs dissolved oxygen

ph value of city water

initial ph value of

ph vs conductivity

lower ph value

ph value increases

lower level of city

varying level graph