Kim 1
Dongho Kim
Nov. 11th, 2013
Chem 111-101
TA : Kristi Liddell
Group Members : Rajan Konai
Urjita Khera
Parvaneh Largani
Sam Lapp
Dongho Kim
“How is our daily water looks like?”
Kim 2
Dongho Kim
Chem 111 Lab Report
Liddell Chem111-101
Due Date (11/11/13)
“How is our daily water looks like?”
<Introduction>
In a daily life, we usually drink water without any worry from a sink of our houses
since we believe that the water is clean and pure. We probably may know that our water is
coming from pipelines from underground manufactured by a local water company. However,
we don’t really consider how the water comes from and how clear the water is. In order to
check our daily water’s purity, we can use a data of water hardness by having some
experiments called EDTA and AA so that we can distinguish what kinds of water is clean and
pure.
When we hear the word ‘water hardness’, it doesn’t feel common word in our daily
life and also it doesn’t really mean how hard the actual water is. The definition of ‘water
hardness’ is the transferred value of Calcium Carbonate from stored amount of Calcium and
Magnesium in natural water.1) The unit of this value is called ‘ppm’ which is parts per million.
The water that we have been drunk from sink of kitchen or some public places, doesn’t really
harmful enough to affect our health badly, but it is important to know that ‘water hardness’
shows us how much Calcium and Magnesium are contained in natural water. It means that if
a water hardness had a more Calcium but fewer Magnesium, it would be really healthy for
our bodies because it may leads us to prevent some circulatory or heart disease according to
some research results.2) On the other hand, Magnesium doesn’t really affect to us in a good
way as we know because it could occur dehydration phenomenon by absorbing much
Magnesium such as sea water which has a lot of Magnesium than Calcium. Therefore, if the
value of water hardness is high, it doesn’t really mean that the water is good water or not.
That is the main reason why we need to check the water contains more Calcium and fewer
Kim 3
Magnesium.
To measure water hardness, there are two widely known ways to get those
ingredients. Those are called ‘EDTA (Ethylenediaminetetraacetic Acid)’ Titration and ‘AA
(Atomic Absorption Spectrophotometry)’. These two words sound really difficult and
complicated, but these two methods are pretty interesting and amazing experiments to do.
First of all, EDTA titration is an experiment to get value of water hardness (or Divalent
Cation Concentration) of Calcium or Magnesium by using EDTA into a natural water sample
with NH3/NH4 Buffer which is an aqueous solution that contains weak acid and conjugate
base or weak base and conjugate acid with Ammonia and Ammonium and also EBT indicator.
The other experiment, AA, is a specific way to measure the concentration of Calcium and
Magnesium divalent ions by absorbing sample water and also burning it into the flame so that
it could be measured by reflecting on the spectroscopy in the AA experiment. These two
experiments are used in a same way but EDTA experiment also reacts with all divalent ions
and not just Calcium and Magnesium.
In order to compare hardness of water, there should be different water samples from
different locations so that we could see which area has less or more minerals in the water.
Thus, we have 5 different locations, a private apartment (off campus) and four different halls
in PSU dormitories. Before having these experiments, the writer (my personal thoughts)
believed that a private apartment which was the writer’s location might have less hardness
than other locations since the location is private property, there might be less amount of
transferring water which means less contact with limestone in pipelines from a local water
company. There might be lots of pipelines and more amount of transferring water under the
dormitories’ undergrounds which meant the water in the dormitories might contacts more
limestone in the pipelines than the writer’s.
Kim 4
<Procedure>
Each group member started to have their own experiment with their own water
sample from different locations. The locations of water samples should not be the same since
the purpose of this experiment was based on the comparison of water hardness from different
locations. According to the steps in PSU Chemtrek written by Stephen Thompson pages 10 –
15 to 10 – 223), each member of the group took their own sample and followed the steps from
the Chemtrek.
First of all, every member was provided with a little foil on their desks. They were
asked to put their own water sample as few drops and also distilled water and Calcium
Chloride. Then, they brought that foil to the hot plate burner and waited until all liquids were
evaporated. This is a small experiment to see the differences between the liquids’ residues on
the foil after evaporations.
After the evaporations, each member started to have EDTA titration experiment to
perform on each water sample as its original sample and after that they began to mix with
softening agent. There were commercial conditioning products for mixing with the water
samples and each member mixed with this product just a little bit with their own water. They
were asked to put one drop of NH3/NH4/MgEDTA buffer and EBT indicator in their water
samples and these were experienced with the 1*12 strip. At this experiment, every member
must drop the products accumulatively in every well so that EDTA solutions were titrated.
There should be some color changes by these drops in the 1*12 strip. When the color
changed, each member were asked to record the number of well that was changed. The reason
why he/she should record the number of well is that the number of EDTA drops in that well
will be used in the equation of EDTA to determine the value of water hardness.
Comparing with the EDTA titration experiment, AA experiment was pretty simple
and easy to measure. Every member went to the specific laboratory that had two AA
Kim 5
instruments to measure each value of Calcium and Magnesium of their own water samples.
At first, each member was asked to put the absorbing pipe into his/her own water sample, and
press measure button to measure the value of Calcium or Magnesium. This value could be
measured by the aerosol in the water and the monochromatic light through the sample. Since
the water sample was absorbed by the instrument, it went to the flame to make a light which
was occurred the wavelength of the light. The light from the AA instrument began to measure
the wavelength of light which is responded to an excited electron of metal and went to the
Monochrometer to measure the amount of absorbance by using spectroscopy principle. The
measurements from the AA instruments were also known as concentration of Calcium and
Magnesium by the first two calibration lines that were created at the experiments. Every
member recorded the concentrations on their own notes.
<Results>
The observations that our members got from their own foils at the beginning of this
experiment were like:
Figure 1: Difference between Water sample after evaporation.
Off Campus
East Dorm
Two concentric
West Dorm
South Dorm
Concentric
Concentrated in
white cloudy &
Water Sample
Center Dorm
Concentrated in
white rings and
Two concentric
the middle of
little bit thick
the middle but
concentrated in
white rings
the sample
rings
had a white ring
the middle
Distilled
Evaporated
Evaporated
Evaporated
Evaporated
Evaporated
CaCl2
Evaporated
Evaporated
Evaporated
Evaporated
Evaporated
According to this table, every water sample had something residue on the foil but
Kim 6
nothing left from the distilled and CaCl2. This phenomenon was lead us to expect that there
were some amount of Calcium and Magnesium in our water sample which were distilled one.
Figure 2: 1st calibration graph of Ca2+.
1st Absorbance (at 422.7nm) vs.
Ca Concentration (ppm) graph
Absorbance (nm)
0.6
y = 0.0101x + 0.0261
R² = 0.9916
0.4
Concentration (ppm)
0.2
Linear (Concentration
(ppm))
0
0
10
20
30
40
50
60
Ca Concentration (ppm)
Figure 3: 2nd Calibration graph of Mg2+
2nd Absorbance (at 202.5nm) vs.
Mg Concentration (ppm) graph
Absorbance (nm)
0.5
y = 0.0127x + 0.0152
0.4
R² = 0.9984
0.3
Concentration (ppm)
0.2
Linear (Concentration
0.1
(ppm))
0
0
10
20
30
Mg Concentration (ppm)
40
Kim 7
These are the Calibration graphs that our class members got at the certain time. This
was not a constant measurement; it could be changed a little bit.
Figure 4: The value of Calcium and Magnesium from the AA.
Absorbance Value
ppm hardness
Ca2+
0.5586
131.81 ppm
Mg2+
0.3717
115.51 ppm
Total Hardness
247.32 ppm
From the Calibration graphs that we got above, we could use the equation which is slope of
the tangent line (y = 0.0101x + 0.0261) to solve the Ca2+ absorbance in terms of x:
0.5586 = 0.0101x + 0.0261
0.5325 = 0.0101x
X = 52.72 ppm of Ca2+
This is not the final ppm value of Ca2+. We must multiply divalent cation Ca2+ times the ratio
of the molar mass of CaCO3. So, the final ppm value would be:
52.72ppm * (100g of CaCO3 / 1mole) / (40g of Ca2+ / 1mole) = 131.81 ppm hardness.
It is same calculation principle for Magnesium absorbance.
From the Calibration graphs that we got above, we could use the equation which is slope of
the tangent line (y = 0.0127x + 0.0152) to solve the Ca2+ absorbance in terms of x:
0.3717 = 0.0127x + 0.0152
0.3565 = 0.0127x
X = 28.07 ppm of Mg2+
Kim 8
We also need to multiply divalent cation Mg2+ times the ratio of the molar mass of CaCO3. So,
the final ppm value would be:
28.07 ppm * (100g CaCO3 / 1mole) / (24.3g of Mg2+ / 1mole) = 115.51 ppm hardness.
Figure 5: Total hardness of water samples in different locations.
Absorbance Value
ppm hardness
Ca2+
0.3601
82.67 ppm
Mg2+
0.2581
78.71 ppm
East Hall Total Hardness
161.38 ppm
Ca2+
0.4231
98.27 ppm
Mg2+
0.3254
100.52 ppm
West Hall Total Hardness
198.79 ppm
Ca2+
0.2403
53.02 ppm
Mg2+
0.1885
56.16 ppm
South Hall Total Hardness
109.18 ppm
Ca2+
0.3354
76.56 ppm
Mg2+
0.2530
77.06 ppm
Center (Pollack) Hall Total Hardness
153.62 ppm
Figure 6: The value of Calcium and Magnesium from EDTA Titration.
Drops of EDTA
ppm hardness
Water Sample
11
220ppm
Softened Sample
8
160ppm
How do we get the ppm hardness of EDTA Titration? We need to use an equation which is
M1*V1 = M2*V2 to get the concentration of the divalent cations.
Kim 9
2*10-4 * 11 drops = M2 * 1drop
0.0002 * 11 = M2
M2 = 0.0022 mol of CaCO3
This is not the final value of EDTA ppm. We must multiply CaCO3 molar mass with the
concentration of CaCO3 and convert it into mg unit of CaCO3:
(0.0022 mol of CaCO3 / liter) * (100g CaCO3 / mol CaCO3) *
(1000mg CaCO3 / 1g CaCO3) = 220 mg CaCO3 / liter.
Since we know that the density of water is 1mg CaCO3 / 1000g water = 1ppm, we can
calculate the ppm hardness which would be:
( 220mg CaCO3 / 1000g water ) = 220 ppm hardness.
One of the questions (Q6) in PSU Chemtrek, we need to calculate the hardness as grains per
gallon. We can convert hardness to grains per gallon by using 17.1 ppm which is equal to 1
grain CaCO3 / gallon. Thus, the calculation would be:
220 ppm * (1 grain per gallon / 17.1 ppm) = 12.86 grains per gallon.
Figure 7: Total EDTA hardness of both water sample and softened sample.
East Hall
Water Sample
Softened Sample
West Hall
Water Sample
Softened Sample
South Hall
Water Sample
Softened Sample
Center (Pollack) Hall
Water Sample
Softened Sample
Drops EDTA
ppm hardness
12
240 ppm
7 (3:1)
140 ppm
3
60 ppm
8
160 ppm
5
100 ppm
5
100 ppm
10
200 ppm
5
100 ppm
Kim 10
Figure 8: The differences between AA and EDTA.
Difference between
AA hardness
EDTA hardness
AA and EDTA
Off Campus
247.32 ppm
220 ppm
27.32
East Hall
161.38 ppm
240 ppm
-78.62
West Hall
198.79 ppm
60 ppm
138.79
South Hall
109.18 ppm
100 ppm
9.18
Center (Pollack) Hall
153.62 ppm
200 ppm
46.38
<Discussion>
To compare with the writer’s hypothesis and the results from the AA and EDTA
experiments, his hypothesis was not that wrong since the hardness of water could be changed
based on the geological issues and also taste of water. According to the data, every member
had the experiments with their water samples which were brought by pretty much different
area. There might be some geological height differences between each location surely6).
When we look at the measurements of hardness of off campus and West hall, the values were
pretty high located around 200 ppm which meant high hardness value5). Plus, the values from
the South and Center halls were treated as moderately hard5). The water from the East hall
was treated as hard hardness5). Therefore, there would be some water hardness differences
between the geological issues. It could be harder or softer than each other. The data between
AA and EDTA are pretty much different than we expected because the differences were pretty
bigger than we thought. However, the off campus and South Hall values were not that bad
enough to get accurate data since the difference between AA and EDTA were less than 20 ~
Kim 11
30 ppm. Plus, we could realize that EDTA measured residue of sample, caused by
evaporation. Generally EDTA was added when TDS is done unlike AA molecule, and EDTA
measured only left over substances. Therefore, there should be different measurements
between those two experiments.
According to the Department of Health in North Dakota4), there might not affect the
taste of water by reducing the Ca2+ and Mg2+, but it could be a little bit different by
comparing the hardness between the hilly section and lower section. We could guess that Off
Campus, West Hall, and East Hall could be hilly sections around this local area by comparing
the water hardness and the residues on the foil at the beginning of the laboratory. When we
looked at the Figure 1, most of residue came out with white rings and it usually concentrated
in the middle. But there could be a little bit difference in thickness between five of them.
When the residue from off campus was evaporated, it came out really thick white two rings
compared to the others. It might mean that there would be more minerals (Ca2+ and Mg2+).
On the other hand, the water samples from lower section, South and Center (Pollack) Halls,
also came out with white ring residues (not that thick as off campus one), but it came out with
lower AA hardness than other locations which meant Calcium and Magnesium might be
contained little bit less than hilly section samples. Thus, it could also be interpreted as lower
water hardness might affect taste of water theoretically.
<Conclusions>
From this experiment, I could have an opportunity to see and observe seriously when
I use or drink water from my house or any public place. The water from the underground or
the rain from the sky actually affects the hardness of water that we usually use in our daily
life. According to the EDTA and AA experiments, the value (=hardness of water) could be
changed to softened or also could be changed to hardened which meant there might be a little
Kim 12
bit taste difference between underground water that not contacted with the air but rocks
contained with minerals and the water from the ground. Since we realized that the softening
agent products (such as Brita) by reducing the hardness of water, we could use it as much
better tasty and healthier use personally.
<References>
1) USGS Water – Quality Information
<http://water.usgs.gov/owq/hardness-alkalinity.html>
2) Calcium
<http://heart.kumu.org/calcium.html>
3) Thompson, Stephen. PSU Chemtrek. Joseph T. Keiser, 2013 – 2014 version, pgs. 10 –
15 to 10 – 22.
4) Department of Health, Ground of water, North Dakota (January 6th, 2013)
<http://www.ndhealth.gov/wq/gw/pubs/mineral.htm>
5) Hard/Soft Classification
<http://en.wikipedia.org/wiki/Hard_water>
6) Water Hardness - Penn State Library
<http://www.libraries.psu.edu/content/dam/psul/up/emsl/documents/Openfile%20report%2081-329%20%20Groundwater%20quality%20and%20data%20on%20wells%20and%20springs%
20in%20PA,%20v.2.pdf>