Purpose
The Purpose of this experiment was to determine the pH, conductivity, total and phenolphthalein
alkalinity, and the hardness of the four drinking water samples that was obtained from different
locations. Another purpose was that this experiment was to see what makes the water we drink
everyday drinkable, and exactly what is contained in the drinking water. Overall, by making
observation and analyzing the different water samples through this experiment, it was
determined that not all water is pure and chlorine free.
Procedure
Materials:
Laptop
pH Probe
Logger Pro Program
Serial Box interface
100 mL Beaker
Conductivity Probe
Erlenmeyer Flask
Buret Clamp
Stirring Rod
50.00mL Buret
pH 4 Buffer
pH 7 Buffer
pH 10 Buffer
Low-range Solution
Mid-range Solution
Phenolphthalein
Mixed indicator (bromocresol green/methyl red)
10% Thiosulfate Solution
UniVer3
0.0100 M Hydrochloric Acid (HCl)
0.0100 M EDTA (Ethylenediamineterraacetate acid)
DI water
Four Water Sample
SAFETY CAUTION
AVOID INGESTING OR INHALING THE CHEMICALS USED IN THIS LAB.
Thiosulfate solution can may cause irritation to skin and eyes.
Bromocresol green and methyl red may cause irritation to skin, eyes and respiratory tract.
Phenolphthalein is flammable and irritating.
Avoid contact with eyes, skin, and clothing.
HCl Is toxic and corrosive.
EDTA is an eye irritant.
pH Test
1. pH probe was set up and the LoggerPro program was opened on the laptop.
2. Open the Exp. 4 Acid/Base Titration on the laptop
3. Rinse the pH probe with the Distilled water.
4. Calibrate the pH probe using a two-point calibration with the pH 7 and pH 10 buffers.
5. Obtain 50-mL of the water sample and transfer it into a clean, dry beaker.
6. Immerse the pH probe into the beaker; wait till the pH meter window stabilizes. Record
the pH of the water.
7. Analyze the sample’s pH twice.
8. Repeat the steps 5-6 for the other water samples.
Conductivity Test
9. Conductivity probe was set up and the Exp. 14 Conductivity was opened on the laptop.
10. Double check to see that the switch box is set to 0-2000 µS/cm. If not set it to 0-2000
µS/cm.
11. Rinse the conductivity probe with the Distilled water.
12. Calibrate the conductivity probe using a two-point calibration with the low and mid-range
solutions.
13. Transfer 50-mL of the water sample into a clean, dry beaker.
14. Immerse the conductivity probe into the beaker; wait till the conductivity meter window
stabilizes. Record the conductivity of the water.
15. Analyze the sample’s conductivity twice.
16. Repeat steps 13-15 for the other water samples.
Total and Phenolphthalein Alkalinity Tests
17. Obtain 50-mL of the water sample and transfer it into a clean, dry Erlenmeyer flask.
18. Rinse the 50-mL buret first with the distilled water and then rinse it with the HCl. Then
set up the buret on the support stand using a buret clamp.
19. Place the Erlenmeyer flask under the buret.
20. Add three to five drops of phenolphthalein solution into the sample.
21. Record the initial reading on the buret and the initial color of the solution.
22. Titrate the solution until the solution changes color reaching its endpoint. (It will usually
be colorless.)
23. Record the final reading on the buret and the final color of the solution.
24. Add a few drop of 10% thiosulfate solution into the flask.
25. Add three to five drops of the mixed indicator, bromocresol green/methyl red into the
flask.
26. Record the initial reading on the buret and record the initial color of the solution.
27. Titrate the solution until it changes color.( If the solution was initially green then the endpoint of the solution should be faint straw-colored.)
28. Record the final reading on the buret and the final color of the solution.
29. Repeat steps 17-28 for the other water samples.
Total Hardness Test
30. Obtain 50-mL of the water sample and transfer it into a clean, dry Erlenmeyer flask.
31. Rinse the 50-mL buret first with distilled water and then rinse it with the EDTA solution.
32. Add one scoop of UniVer3 indicator to the Erlenmeyer flask.
33. Record the initial reading on the buret and the initial color of the solution.
34. Titrate the solution until it changes color. (If the solution was initially reddish-pink, then
the end-point of the solution should be light blue.)
35. Record the final reading on the buret and the final color of the solution.
36. Repeat steps 30-35 for the other water samples.
Data
Name
Won Joon
Evan
Sarah
Kyle
The Location Water Sample Obtained
Carlson Library 1st floor drinking fountain
Bellevue
Well Water
Rec Center
1. pH
Location
Carlson Library
Bellevue
Well Water
Rec Center
2. Conductivity
Location
Carlson Library
Bellevue
Well Water
Rec Center
Color
Clear
Clear
Clear
Clear
[OH-]
2.2x10-7M
3.3 x10-7M
3.5 x10-8M
3.3 x10-7M
pH
7.34
7.52
6.55
7.52
µS/cm
327 µS/cm
503 µS/cm
546 µS/cm
320 µS/cm
When
3/25 4:59pm
3/24 10:04pm
3/24 5:52pm
3/25 1:56pm
mg/L
164 mg/L
252 mg/L
273 mg/L
160 mg/L
Morality of HCl: 0.0100M
3. Total and Phenolphthalein Alkalinity
Carlson
Initial
Final Color Initial Reading
Library
Color
(mL)
Phenolphthalein
Mixed Indicator
Pink
Light Blue
Bellevue
Initial
Color
Colorless
22.20
Light
22.40
Purple
Final Color Initial Reading
(mL)
Phenolphthalein
Mixed Indicator
Well Water
Pink
NA
Initial
Color
Colorless
10.06
NA
10.82
Final Color Initial Reading
(mL)
Phenolphthalein
Mixed Indicator
Rec Center
Colorless
Colorless
Initial
Color
Colorless
24.29
Light Pink
24.29
Final Color Initial Reading
(mL)
Phenolphthalein
Mixed Indicator
Pink
Light Blue
Colorless
Peachy Pink
26.95
29.38
ppm
164 ppm
252 ppm
273 ppm
160 ppm
Final
Reading
(mL)
22.40
25.10
Volume used
(mL)
Final
Reading
(mL)
10.82
12.10
Final
Reading
(mL)
24.29
34.49
Final
Reading
(mL)
29.38
29.54
Volume used
(mL)
0.20
2.70
0.76
1.28
Volume used
(mL)
0.00
10.20
Volume used
(mL)
2.43
0.16
*Evan did not provide the initial and the final color change of the mixed indicator.
Phenolphthalein Alkalinity
Total Alkalinity
M
ppm
M
ppm
-5
-4
Carlson Library
4.4x10
2.2
5.8x10
29.0
Bellevue
1.5 x10-4
7.6
4.1 x10-4
20.4
-3
Well Water
0.00
0.00
2.04 x10
102
-4
-4
Rec Center
4.86 x10
24.3
5.18 x10
25.9
*Sarah’s well water did not change color when phenolphthalein was added, it was colorless.
4. Hardness
Initial Color
Final Color
Initial Reading (mL)
Final Reading (mL)
Volume used (mL)
Total Hardness (ppm)
Total Hardness (M)
Carlson
Library
Pink
Purple/Blue
26.25
31.90
5.65
56.5
1.13x10-3
Bellevue
Well Water
Rec Center
Pink
Blue
22.90
28.14
5.24
52.4
1.05 x10-3
Pink
Blue
13.75
27.41
13.66
136.6
2.73 x10-3
Pink/Red
Blue
21.95
26.11
4.16
41.6
8.32 x10-4
Sample Calculations
Vol. = Volume
Avg. =Average
M = Morality
ppm= parts per million
0.100mL HCl =1.00ppm CaCO3
0.100mL EDTA =1.00ppm CaCO3
1
2
pH
Average pH
pOH
Avg. pH = (|1st data-2nd data|)/2
Avg pH = (|7.34-7.33|)/2
=7.34
pOH = 14- pH
pOH = 14-7.34
= 6.66
Conductivity
Avg. Conductivity
Avg. Conductivity = (|1st data2nd data|)/2
Avg. Conductivity = (|331-323|)/2
=327 µS/cm
mg/L
2000 µS/cm = 1000mg L
(2 µS/cm)/(1mg/L) = (avg
cond.)/(x mg/L)
(2 µS/cm)/(1mg/L) =
(327 µS/cm)/(x mg/L)
X= 164 mg/L
Hydroxide Concentration [OH]
[OH-] = 10-pOH
[OH-] = 10-6.66
= 2.2x10-7M
ppm
1 mg/L = 1 ppm
164 mg/L = 164 ppm
3
3
Alkalinity
Vol. of HCl used for phenolphthalein = Final Buret Reading-- Initial Buret Reading
= 22.40mL – 22.20mL
= 0.20mL HCl
Phenolphthalein Alkalinity (M) = Vol. of HCl used (0.0100M/ 50.00mL)
= 0.20 mL (0.0100M/ 50.00mL)
= 4.4x10-5 M
0.100mL HCl =1.00ppm CaCO3
Phenolphthalein Alkalinity (ppm) = Vol. of HCl used (1.00ppm CaCO3/0.100mL)
= 0.20mL (1.00ppm CaCO3/0.100mL)
= 2.2 ppm
Total Vol. of HCl = Total Alkalinity
Total Vol. HCl used = Vol. of HCl used for phenolphthalein + Vol. of HCl used for
bromocresol
green/ methyl red
= 0.20mL + 2.70mL
= 2.90mL
Total Alkalinity (M) = Total alkalinity (0.0100M/ 50.00mL)
= 2.90mL (0.0100M/ 50.00mL)
= 5.8x10-4 M
Total Alkalinity (ppm) =Total alkalinity (1.00ppm CaCO3/0.100mL)
= 2.90mL/(1.00ppm CaCO3/0.100mL)
= 29.0 ppm
4
Hardness
0.100mL EDTA =1.00ppm CaCO3
Vol. of EDTA used for phenolphthalein = Final Buret Reading-- Initial Buret Reading
= 26.25mL -- 31.90mL
= 5.65 mL
Total Hardness (M) = Vol. of EDTA used (0.0100M/ 50.00mL)
= 5.65 mL (0.0100M/ 50.00mL)
= 1.13x10-3
Total Hardness (ppm) = Vol. of EDTA used (1.00ppm CaCO3/0.100mL)
= 5.65 mL/(1.00ppm CaCO3/0.100mL)
= 56.5 ppm
Discussion
There are several different methods to analyze the quality of water. A pH test is one of the ways
the quality of water is analyzed. According to the EPA, the recommended range a pH of water
should be maintained between 6.5 and 8.5 (U.S. Environmental Protection Agency, 2010). The
pH value determines whether water is alkaline, acidic or neutral. Water with a pH value lower
than a 6.5 is considered acidic, soft and corrosive. This low pH level could cause damages to the
metal piping and could possibly be a health risk. Water with a pH value higher than an 8.5 is
considered hard and even though this does not pose any health risks but it can cause aesthetic
problems. (Free Drinking Water). In this experiment four water samples were obtained from
different locations: 1st floor of Carson Library, well water from Sarah’s house, regular water
from Evan’s house, and water from the university Rec. Center. All water samples had similar pH
values: 7.34, 6.55, 7.52 and 7.52. This indicated that the entire water sample that was obtained
was in a acceptable pH range. pH level is considered a secondary standard, which means that pH
range of 6.5 to 8.5 is unenforced water contamination level set so that some contaminants could
be reduced and provide a acceptable aesthetic qualities for the public water system. (Extension
Extra 1).
The second method was the conductivity test. The conductivity measures how much electrical
current a solution is able to carry out. The reason a solution can carry an electrical current is
because conductivity of water is directly related to the number of dissolved free ions that are
present in the solution (SDWF). So by performing the conductivity test, you are measuring the
total dissolved solid (Water Quality) which are composed of substances such as: bicarbonate,
calcium, magnesium, sulfate, chloride, sodium, and potassium (Kippenhan, 2009). TDS, like the
pH value is considered a secondary contaminants that affect the aesthetic quality of water (U.S.
Environmental Protection Agency, 2010). Although the water with TDS below 1000 mg/L is
usually acceptable to humans, the maximum TDS value assigned by the Environmental
Protection Agency is 500 mg/L (Health Canada).The result of this experiment showed that the
water that was obtained from the Rec. Center and the Carlson Library had the similar TDS
values and the two water sample that was obtained outside of campus had similar TDS values.
The possible reason for this might be because both the Rec. Center and the Carlson Library’s
water are supplied by the same pipeline. Whereas the water sample obtained from outside
campus could be supplied by a different one. However, all four water sample had TDS values
below 1000 mg/L indicating that they are all in the acceptable range of TDS.
Another method that was used to test the water was the total and phenolphthalein alkalinity test.
Alkalinity is the measure of the total amount of basic groups in a sample such as carbonate,
bicarbonates, and sulfates (Kippenhan, 2009). If alkalinity becomes too low, the pH of water
increases. Water that is low in alkalinity can be corrosive and irritating (alkalinity of drinking
water explained, 2005). Although this low alkalinity does not pose any threat to human, it does
cause damage to the pipelines that carry the water. Therefore, it is important to maintain the
alkalinity level in order to prevent the pipeline from corrosion (SDWF). The water sample that
had the lowest phenolphthalein alkalinity value was the well-water. This had a value of 0.00. The
water sample obtained from the Rec. Center and Bellevue had the highest phenolphthalein
alkalinity value. The water sample obtained from the Carlson Library had a pretty low
phenolphthalein alkalinity value.
Finally, the hardness of the water samples was tested. Hard water is water that contains large
amounts of cations (Search.com). The most common ones contain ions such as calcium ions and
magnesium ions. (US Environmental Climate Change). Although these ions do not cause any
health problems, but they can be involved in reactions that form insoluble precipitates. Water
with hardness greater than 200mg/L can cause mineral deposition such as calcium carbonate
(Search.com).
Ca+ 2(aq) + HCO3-(aq) -> CaCO3(s) + H2O(l) + CO2 (g)
According to the above equation calcium ions react with bicarbonate ions to produce calcium
carbonate solid. Even though these deposits are not harmful to humans, they are difficult to
clean. According to the result, the sample from the well-water had the highest hardness value.
This supports the results from the conductivity and also it makes sense because well-water that
have not been filtered by anything will contain a lot of different minerals, and this will result in
the conductivity to increase which might indicate there might be some ions that causes a increase
in the hardness.
Error Discussion
There might have been some errors that could have occurred during this experiment. One error
could be an error of not adding enough 10% thiosulfate solutions in the flask when testing for the
alkalinity. This might have caused the alkalinity value to increase. This is because thiosulfate
reacts with chlorine and converts into another form. Thus more acid might have been added,
increasing the alkalinity of the water sample.
An error that could have affected the pH and the conductivity of the water sample might have
been not washing and drying the beaker properly. Before transferring the water sample to the
beaker, the beaker was washed thoroughly with the tap water, but it was not dried properly. This
might have affected the pH of the water sample because of the water inside the beaker by
causing the water sample’s pH to be closer to that of tap water. Also when this bottle was
obtained from the instructor, it should have been rinsed with the water sample before the sample
was taken. This might have caused some of the values to be higher or lower than it actually
should have been.
Another possible error could be an error of misreading the meniscus of the buret. By misreading
the buret the alkalinity and the hardness of the sample might have been off, giving an incorrect
value for the result. Also when titrating the water sample, extra HCl solution could have been
added even though the solution already became colorless. By adding more HCl there could be an
increase in the pH of the water sample.
Conclusion
The purpose of this experiment was to determine the pH, conductivity, alkalinity and the
hardness of each water sample and analyze the quality of the water samples. The water samples
were obtained from the Carlson Library, the well, Bellevue, and the Rec. Center. The pH from
four different locations was similar in value. They are all in the normal pH range of drinking
water. The conductivity of the Carlson Library and the Rec. Center were similar and the well
water and the Bellevue were similar in value. They ranged from 164 mg/L to 273 mg/L, which
suggested that they are below the suggested maximum amount of TDS of 500 mg/L. The water
sample from the Rec. Center and Bellevue had a high phenolphthalein and total alkalinity values.
All four water sample are within a normal range of hardness in a drinking water. However, the
hardness of the well-water was 136.6 ppm, which was higher than the other three samples. The
reason for this is because the water sample is a well-water, and well-water contains a lot of
minerals which might have caused the hardness to be high. Overall, the result showed that water
sample taken from different location was mostly similar in values. However, there are many
different factors, such as time that could cause the result of this experiment to turn out
differently.
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