Research Question: Is water quality safe at Taipei American School?
Type of Variable
Variable
Description / Explanation
Independent Variable
Water Sources
Water was obtained from seven different sources: tap water (from the 1st Floor Science bathroom), bottled water, distilled water, pond water (from the lower school pond), pool water, and dispenser water (from the water dispenser in front of the summer school activities office).
pH was measured using the Vernier pH probe. Dissolved oxygen was measured using the Vernier Dissolved Oxygen probe. Chloride presence was qualitatively tested for according to precipitation formation. Calcium level was quantified by the height of soap bubbles produced.
Control
Temperature, amount of source water, time
The temperature for all water was kept at 24.6°C. The amount of source water used was kept constant through each experiment. The amount of time used before conducting measurements was also kept consistent between trials.
Materials:
Vernier pH probe
Vernier dissolved oxygen probe
Test tubes (7)
Beaker (5 x 100mL, 7 x 600mL)
Graduated cylinder (2 x 10mL, 1 x 25mL, 2 x 100mL)
Volumetric Flask (1000mL)
Dish Soap
Stirring rod
Temperature probes (7)
Water from various sources
Pipettes
Goggles
Gloves
Wash bottle
Stop watches(3)
Hot plate
Calcium Nitrate- Ca(NO3)2
Silver nitrate – AgNO3
5% Nitric acid (100mL) - NO3
Balance
Stopwatches (3)
Black construction paper
Procedure: Before the experiments
Fill each 500mL beaker, each with water from a different source, including tap water (from the 1st Floor Science bathroom), bottled water, distilled water, pond water (from the lower school pond), pool water, and dispenser water (from the water dispenser in front of the summer school activities office).
Put one temperature probe into each beaker. Wait until each sample is at 24.6° C before starting the experiment. If not, use a hot plate to change the temperature.
pH and Dissolved Oxygen Experiments
Calibrate pH and dissolved oxygen probe. The pH probe is calibrated through two-point calibration with buffers of pH 4 and pH 7. The dissolved oxygen probe is calibrated through internal calibration.
Fill 5 of the 100mL beakers with 60mL of tap water.
Using LoggerPro, pH probe, and dissolved oxygen probe, measure the pH value and dissolved oxygen value of the water over a 1 minute time period. Keep the probes in motion while measuring.
Record the average value of the best fit line of the pH and dissolved oxygen graphs.
Repeat steps 3 –4 for 4 more trials of the same sample water.
Repeat steps 2 – 5 for other water sources.
Chloride Presence
Prepare 5% nitric acid in a 500mL beaker.
Prepare a silver nitrate solution using 1.7 grams of silver nitrate and 98mL of distilled water. The silver nitrate solution is light sensitive and is to be kept under a cover made from black construction paper whenever possible.
Prepare a test tube with 25mL of tap water.
Put two drops of nitric acid into the test tube using a pipette. Mix the test tube thoroughly. If there is fizzing, wait until the fizzing stops before continuing to the next step.
Put two drops of silver nitrate solution into the test tube. Mix the test tube thoroughly and record and observations regarding the presence of precipitate.
Repeat steps 3 – 6 for the six other water sources.
Calcium Hardness
Pour 40mL of the water sample into a 100mL graduated cylinder.
Add 0.4mL of soap into the graduated cylinder.
Shake the cylinder up and down 3 times.
Let the solution settle for 2 minutes.
Measure the height of the soap bubbles using a ruler.
Repeat steps 2-5 for 4 more trials
Repeat steps 1-6 with the other water samples.
Create a hard water sample by mixing 110mg of calcium nitrate into 500mL of tap water.
Repeat steps 1-6 with the hard water sample.
Data Collection
Table 1 – pH Values of Different Water Sources
Water Source
pH Values (1 - 7)
Trials
1
2
3
4
5
Tap
6.21
6.32
6.38
6.42
6.42
Bottled
7.96
7.64
7.50
7.85
7.75
Distilled
6.88
7.80
7.90
6.99
6.22
Pond
7.39
7.19
7.16
7.21
7.17
Pool
6.50
6.87
6.85
7.06
7.17
Fountain
6.39
6.30
6.28
6.28
6.25
Dispenser
7.74
7.55
7.23
6.66
5.77
Table 2 – Dissolved Oxygen Values of Different Water Sources
Water Source
Dissolved Oxygen (mg/L)
Trials
1
2
3
4
5
Tap
4.40
3.20
3.00
3.60
2.90
Bottled
1.90
2.20
2.10
2.20
2.20
Distilled
2.30
3.70
2.00
2.20
2.10
Pond
2.80
1.80
3.20
3.20
2.80
Pool
2.90
2.70
3.00
2.90
3.10
Fountain
4.70
3.80
5.40
3.50
4.00
Dispenser
1.80
2.00
2.20
2.20
1.70
Table 3 – Presence of Chloride – Precipitate Observations
Water Source
Precipitate Present (Yes / No)
Data Observations
Tap
Yes
A medium amount of precipitate formed, showing moderate chloride levels.
Bottled
Yes
Very little precipitate formed, showing a very low chloride levels.
Distilled
No
No precipitate observed, showing that an unobservable, insignificant amount of chloride.
Pond
Yes
A medium amount of precipitate formed, showing moderate chloride levels.
Pool
Yes
A high amount of precipitate formed, showing high chloride levels.
Fountain
Yes
A medium amount of precipitate formed, showing moderate chloride levels.
Dispenser
Yes
Some precipitate observed, showing low chloride levels.
Table 4 - Calcium Hardness of Water Test- The Height of Soap Bubbles
Trial 1 (cm)
Trial 2 (cm)
Trial 3 (cm)
Trial 4 (cm)
Trial 5 (cm)
Average (cm)
Fountain water
9.00
8.60
8.50
9.00
8.80
8.78
Distilled water
11.5
11.2
11.2
11.4
12.0
11.46
Pool Water
5.00
5.40
5.60
5.20
5.30
5.30
Water dispensers
7.00
7.50
7.30
7.10
7.50
7.28
Pond water
7.00
7.00
6.70
6.60
7.00
6.86
Bottled water
5.00
5.20
5.10
5.40
5.00
5.14
Tap
9.30
9.00
9.00
8.80
8.60
8.94
Calcium
5.80
5.90
6.00
5.90
6.10
5.94
Data Processing & Analysis Table 5 – Average pH Value and Standard Deviation of Different Water Sources
Water Source
Average pH Values (1 - 7)
Standard Deviation
Tap
6.35
0.088
Bottled
7.74
0.179
Distilled
7.16
0.698
Pond
7.22
0.095
Pool
6.89
0.256
Fountain
6.30
0.053
Dispenser
6.99
0.795
Sample Calculation (for Tap Water):
Standard deviation was calculated using Microsoft Excel 2007.
Using the average and standard deviations of the pH values, the following was determined: Tap and fountain water had pH values significantly lower than the optimum pH value drinking water (pH 7.5).
Table 6 – Average Dissolved Oxygen Value and Standard Deviation of Different Water Sources
Water Source
Average Dissolved Oxygen (mg/L)
Standard Deviation
Tap
3.42
ottled
2.12
0.130384048
Distilled
2.46
0.702139587
Pond
2.76
0.572712843
Pool
2.92
0.14832397
Fountain
4.28
0.766159252
Dispenser
1.98
0.228035085
Sample Calculation (for Tap Water):
Graph 1 - Average pH Value of Different Water Sources
Error bars were drawn using standard deviation values.
Graph 2 - Average Dissolved Oxygen Value of Different Water Sources
Error bars were drawn using standard deviation values.
Graph 3 - Testing for Calcium: Height of Soap Bubbles
Conclusion
Hardness of water: From the results, it can be inferred that calcium reduces bubble formation. Soap produces less bubbles with calcium and magnesium because it reacts to form the calcium or magnesium salt of the organic acid of the soap. These salts form the grayish scum in the bubbles, and reduces the amount of bubble that can be formed. The bottled water has the lowest height of bubbles formed, while the distilled water has the highest height of soap bubbles. The fountain water is found to be in the middle. The bottled water may have other minerals that would affect the results. However, "hard water" is not a health hazard because it contributes a very small amount of calcium towards daily intake needs.
Evaluation
Hardness of water: It is very hard to determine the height of bubbles. We weren't sure where the bubbles ended, as there were many different types of bubbles. Closer to the solution, the bubbles were small and concentrated, and further higher in the test tube, the bubbles became bigger and less in number. The big bubbles could have reached to the top of the test tube, but the small bubbles did not take up a lot of space. We tried to make the measuring of the bubbles consistent by measuring the small bubbles only, but there could have also been a big systematic error as it was hard to determine where the small bubbles end and the big bubbled begin. To decrease the systematic error, more trials should have been run for each of the water samples so a general norm of height can be found.
Another potential error was that different people shake the cylinder differently, therefore creating a variation in results. The force of each shake was also different, so the height from the resulting shakes would vary. The same person should have shook the test tubes and try to shake the tubes with consistent force. Another systematic error is in the measuring of the amount of soap. 0.4 ml is very hard to measure out.
Dissolved oxygen was measured using the Vernier Dissolved Oxygen probe.
Chloride presence was qualitatively tested for according to precipitation formation.
Calcium level was quantified by the height of soap bubbles produced.
The amount of source water used was kept constant through each experiment.
The amount of time used before conducting measurements was also kept consistent between trials.
Materials:
Procedure:
Before the experiments
pH and Dissolved Oxygen Experiments
- Calibrate pH and dissolved oxygen probe. The pH probe is calibrated through two-point calibration with buffers of pH 4 and pH 7. The dissolved oxygen probe is calibrated through internal calibration.
- Fill 5 of the 100mL beakers with 60mL of tap water.
- Using LoggerPro, pH probe, and dissolved oxygen probe, measure the pH value and dissolved oxygen value of the water over a 1 minute time period. Keep the probes in motion while measuring.
- Record the average value of the best fit line of the pH and dissolved oxygen graphs.
- Repeat steps 3 –4 for 4 more trials of the same sample water.
- Repeat steps 2 – 5 for other water sources.
Chloride PresenceCalcium Hardness
Data Collection
Table 1 – pH Values of Different Water Sources
Table 2 – Dissolved Oxygen Values of Different Water Sources
Table 3 – Presence of Chloride – Precipitate Observations
Table 4 - Calcium Hardness of Water Test- The Height of Soap Bubbles
Data Processing & Analysis
Table 5 – Average pH Value and Standard Deviation of Different Water Sources
Sample Calculation (for Tap Water):
Standard deviation was calculated using Microsoft Excel 2007.
Using the average and standard deviations of the pH values, the following was determined:
Tap and fountain water had pH values significantly lower than the optimum pH value drinking water (pH 7.5).
Table 6 – Average Dissolved Oxygen Value and Standard Deviation of Different Water Sources
Sample Calculation (for Tap Water):
Graph 1 - Average pH Value of Different Water Sources
Error bars were drawn using standard deviation values.
Graph 2 - Average Dissolved Oxygen Value of Different Water Sources
Error bars were drawn using standard deviation values.
Graph 3 - Testing for Calcium: Height of Soap Bubbles
Conclusion
Hardness of water:
From the results, it can be inferred that calcium reduces bubble formation. Soap produces less bubbles with calcium and magnesium because it reacts to form the calcium or magnesium salt of the organic acid of the soap. These salts form the grayish scum in the bubbles, and reduces the amount of bubble that can be formed. The bottled water has the lowest height of bubbles formed, while the distilled water has the highest height of soap bubbles. The fountain water is found to be in the middle. The bottled water may have other minerals that would affect the results. However, "hard water" is not a health hazard because it contributes a very small amount of calcium towards daily intake needs.
Evaluation
Hardness of water:
It is very hard to determine the height of bubbles. We weren't sure where the bubbles ended, as there were many different types of bubbles. Closer to the solution, the bubbles were small and concentrated, and further higher in the test tube, the bubbles became bigger and less in number. The big bubbles could have reached to the top of the test tube, but the small bubbles did not take up a lot of space. We tried to make the measuring of the bubbles consistent by measuring the small bubbles only, but there could have also been a big systematic error as it was hard to determine where the small bubbles end and the big bubbled begin. To decrease the systematic error, more trials should have been run for each of the water samples so a general norm of height can be found.
Another potential error was that different people shake the cylinder differently, therefore creating a variation in results. The force of each shake was also different, so the height from the resulting shakes would vary. The same person should have shook the test tubes and try to shake the tubes with consistent force. Another systematic error is in the measuring of the amount of soap. 0.4 ml is very hard to measure out.
Sources
http://www.water-research.net/hardness.htm
http://chemistry.about.com/cs/howthingswork/a/aa082403a.htm