th

Krupski 2
Introduction:
Originally, water hardness was understood to be a measure of the capacity of water to precipitate soap (1). Soap is precipitated chiefly by the calcium and magnesium ions present.
Thus, it makes sense that presently, total hardness of water is defined as the quantity of divalent cations in the water. There are many different divalent salts; however, calcium and magnesium are the most common sources of water hardness (2). Water hardness if often used as a measure of potable water quality (1). Both magnesium and calcium concentrations are measured as calcium carbonate, in milligrams per liter (or parts per million (ppm)) (1). Here is a water hardness scale from Fairfax Water, Virginia’s largest water utility.
Table 1.1—Water Hardness
Water Hardness Scale
Grains Per
Gallon
Milligrams Per Liter
(mg/L) or Parts Per
Million (ppm)
Classification
Less than 1.0 Less than 17.1 Soft
1.0 - 3.5 17.1 - 60 Slightly Hard
3.5 - 7.0 60 - 120
Moderately
Hard
7.0 - 10.5 120 - 180 Hard
Over 10.5 Over 180 Very Hard
(Explanation of Water Hardness. 5 Jan 2011. Fairfax Water. 6 Oct. 2012 http://www.fcwa.org/water/hardness.htm) (3)
The hardness may range from zero to hundreds of milligrams per liter, depending on the source and treatment to which the water has been subjected (1). Water hardness is important because it measures the quality of the water we are drinking (3).

Krupski 3
Many people to not know that hard water makes up about 85 percent of the nation's drinking water (4). Although hard water possess no health risks, it takes more effort for soap to perform its cleansing action. Ca
2+
and Mg
2+ lower the efficiency of soaps because they react with soap to form precipitates that create an insoluble residue—a grayish soap scum (4). Thus, the harder the water, the less effective people are able to wash their hands. It is interesting to note that under the “Safe Drinking Act Amendments of 1986,” contaminants such as Inorganics like aluminum, copper, zinc, etc. are regulated (1). These water quality standards exist in the
United States and in countries around the world (3). The U.S Environment Protection Agency’s
National Primary Drinking-Water Regulations and National Secondary Drinking-Water
Regulations specify maximum contaminant levels (MCLs) and are health-related legally enforceable rules (5). However, calcium and magnesium are not in this list. Rather, hard water makes cleansing using soap more difficult and can cause scale in industrial boilers and evaporators, narrowing pipes and blocking jets and tubes making is extremely expensive to remove (6).
One way of determining water hardness is EDTA (Ethylenediaminetetraacetic acid) titration. EBT indicator (a blue color) is added to a solution of natural water sample (6). Such indicators can be Eriochrome Black T (EBT) or Calmagite; when added to an aqueous solution containing magnesium ions at a pH of 10.0 +/- 0.1, the solution becomes wine red (1). This is due to the Mg
2+ reacting with the indicator (calcium does not react with the indicator) (6). Next, the EDTA solution is added; it first reacts with the Ca
2+ to form a colorless chelate. Once all the
Ca
2+ has been chelated, the EDTA reacts with the magnesium indicator chelate to produce a colorless MgEDTA chelate. As the Mg 2+ is removed from the indicator, the indicator returns to its blue form. The endpoint is signaled by a sharp change in color of the solution by the indicator

Krupski 4
(7); when all of the magnesium and calcium has been complexed the solution turns from wine red back to its blue color, marking the end point of the titration (1). It should be noted that magnesium ions must be present to yield a satisfactory end point (since the magnesium ions must react with the indicator to give it a wine red color at the start) and that the sharpness of end point increases with increasing pH (1). Also, titrations should be conducted at or near room temperature (which we did) as the color change becomes impractically slow as the sample approached freezing temperature and indicator decomposition becomes a problem in hot water
(1).
Another method is Atomic Absorption Spectrophotometry (AA). A light with discrete energy “E” is projected through a sample of water. The atoms (Mg 2+ or Ca
2+
) have discrete absorbance levels (202.5nm and 422.7nm respectively). (6) The light with the same energy is absorbed by the ions. The ions absorb only this light because they have discrete energy levels
(4). The grating in the spectrophotometer is adjusted to only allow light with energy “E” pass through the narrow slit. Finally, the decrease in intensity from the initial projection is detected by the Photomultiplier tube (PMT). This difference is proportional to the amount of metal in the sample of water (6). Before performing the tests, a set of metal solutions of known concentrations are prepared and analyzed; their data is used to construct a calibration graph for the AA analysis. To check the accuracy and precision of the instrument, the standards are reanalyzed to see how closely they match the correct values—these are known as “Check
Standards” (6).

Krupski 5
A graphic of this process of illustrated below:
Diagram 1.1—Atomic Absorption Spectrophotometry
(http://elchem.kaist.ac.kr/vt/chem-ed/spec/atomic/graphics/aa-expt.gif)
EDTA titration is based on chemical properties and AA is based on light but both come to the same conclusion of water hardness. Being able to use two separate methods to come to the same conclusion, make the results more credible.
Water softening techniques, such as ion exchange, lower the hardness of water. The ion exchange process works by replacing calcium (Ca
2+
) and magnesium (Mg
2+
) ions with monovalent cations (e.g. Na + or H + ), thus reducing the hardness of the water (8). The exchange usually occurs by percolating the water through a column containing the ion exchange material, like a Britta filter (9). It is also possible to soften water with a commercial water-conditioning agent by precipitating Ca
2+ and Mg
2+ ions out of the solution (6). The amount of calcium in domestic and industrial waters is often controlled by water softening techniques (1).
My group took water samples from four different locations. I took water from the sink in the basement floor of Simmons (also known as the globe). K’hadejah took a water sample from
Poland Spring’s bottled water, Rachel took water from her Britta filter which was originally

Krupski 6 collected from the bathroom sink on the 2 nd
floor of East View Halls, and Loren took her water sample from the water fountain from the 5 th floor of Pennypacker Hall (part of East Halls).
Since I do not think that Penn State uses ion exchange water softeners, I hypothesized that the water from the sink and water fountain will both be hard—in fact, I expected that the sink water will be the same as the water from the water fountain. I discovered that some drinking fountains use chillers or filters to improve the temperature and taste of the water but they are all part of the same plumbing system (10). Although it would be interesting to see if Penn State features chillers in highly used water fountains throughout campus, I believed the water hardness would be the same. I predicted that the Britta filter water sample would be softer since it contained ion exchange resin and activated carbon that work together to remove impurities and lessen the hardness of the water (9). Lastly, I think the bottled (purified) water will be the least hard since it has gone through a lengthy deionization process that heavily reduced the hardness of the water
(11).
Procedure: The procedure was taken from the PSU Chemtrek (6). Examining my water sample taken from the sink in the basement of the Simmons dorm, it was found to not be cloudy and there were no particles examined the bulk of the sample. Two extra large pipets were obtained, their stems were cut off and were filled with my diluted sample. The bulk sample of the diluted water was created using 20mL of my sample and 20 mL of distilled water (a 1:1 ratio). The
Atomic Absorption Spectroscopy was performed. Next, the undiluted water sample was evaporated on a piece of aluminum foil next to a distilled water and a 1x10^-3 M Ca
2+ solution to compare dissolved solids in the solution.
Then, EDTA analysis was performed using a 1x12 well for solution of Ca 2+ and Mg 2+ of known concentrations. First, one drop of 1x10^-3 M Ca
2+ solution, one drop of EBT indicator,

Krupski 7 and one drop of NH3/NH4Cl/MgEDTA buffer were added to each of the 12 wells. The wells were titrated serially with 2x10^-4 M EDTA and the first blue well was determined to be the point where excess EDTA was present and thus, the end point of the solution (even though it is slightly past the end point). Next, The well strip was cleaned with distilled water and the titration was repeated but this time one drop of 1x10^-3 M Ca
2+ solution and one drop of 1x10^-3 M
Mg
2+ was used.
Next, to demonstrate water softening with a commercial water-conditioning agent, approximately 20 mg (measured 0.0211g) of Arm + Hammer Super Washing Soda was added to a vial containing my water sample. The hardness after the softening agent was added decreased as expected. Afterwards, a divalent cation removal by ion exchange procedure was performed on a contested sample by using an 8 mL vial with a small amount of cation exchange resin
(enough to cover the bottom of the vial). Finally, the pH of the liquid in the vial (water sample with resin) and water sample by itself were tested.
Results:
Results were taken from Sources 12, 13, and 14, and 15 (see “References” section).
It is important to note that the Sink Water (my sample) and the water fountain sample were both diluted in a bulk sample of 20mL of the original sample and 20 mL of distilled water
(a 1:1 ratio). The Britta filter and Poland Springs Bottled Water were not diluted.
For the known concentration of 1x10^-3 M Ca
2+ solution, well #6 was the first blue well.
Sample calculation #1 shows the 6 th
well corresponding to 𝑀
Ca2+
= 1.2 × 10 −3 𝑀 .

Krupski 8
For the known concentration of 1x10^-3 M Ca
2+ solution and the 1x10^-3 M Mg
2+
, Well
#11 was the first blue well. Sample calculation #2 shows the 11 th well using both of these solution corresponding to 𝑀
Ca2+ and Mg2+
= 1.1 × 10 −3 𝑀 .
Date: 10/23/12
Time: 6:15PM
AA Operator: Brown
Table 1.2-Atomic Absorption Spectrophotometry (AA) Standards for Calcium
Ca
2+
Concentration (ppm)
0
1.000
5.00
10.00
25.0
50.0
Absorbance Value (at 422.7 nm) Check Standard (ppm)
----
0.01168
----
1.10
0.05632
0.11116
0.25653
0.47577
5.21
9.76
24.56
49.25

Krupski 9
Graph 1.1-Calibration Graph for Ca
2+
2+
0,6
0,5
0,4
0,3
0,2
0,1
0
0 y = 0,0094x + 0,0109
R² = 0,9982
10 20 30 40
Ca 2+ Concentration in Parts per Million
50 60
Table 1.3-Atomic Absorption Spectrophotometry (AA) Standards for Magnesium
Mg
2+
Concentration (ppm) Absorbance Value (at 202.5 nm)
0 ----
1.000
5.00
0.01840
0.08981
10.00
25.0
30.0
0.18158
0.40982
0.47531
Check Standard (ppm)
----
1.36
5.08
10.76
24.86
30.24

Krupski 10
Graph 1.2-Calibration Graph for Mg
2+
0,4
0,3
0,2
0,1
0,6
0,5
y = 0,0157x + 0,0118
R² = 0,9979
0
0 5 10 15 20
Mg 2+ Concentration in Parts per Million
25 30 35
Table 1.4- Comparison of Total Dissolved Solids for Water Samples
Sample
Distilled Water
1x10^-3 M Ca
2+
(reference)
Britta Filter
Sink Water
Poland Springs Bottled Water
Water Fountain
Result
No visible residue left
Visible white solid residue
Visible White solid ring—heavier than reference
Substantial White solid ring—heavier than
Britta filter sample
Faint white solid ring—less than Britta, similar to reference
Thick white residue—filled in ring—heaviest sample

Krupski 11
Table 1.5- Atomic Absorption Results
(Sample Calculation #6 - “Concentration of Ca
2+ using graph”)
(Sample Calculation #8 -“Concentration of Mg
2+ using graph”)
(Sample Calculation #7-“ Ca
2+ concentration in CaCO
3
”)
(Sample Calculation #9- Mg
2+ concentration in CaCO
3
)
Sample
Britta
Filter
Sink
Water
Poland
Springs
Bottled
Water
Ca
2+
Mg
2+
Concentration of Ca
2+ using graph
0.0286 0.0981 1.88 ppm
Ca
2+
0.2904 0.2980 29.7 ppm
Ca
2+
0.2356 0.0136 23.9 ppm
Ca
2+
Water
Fountain
0.3429 0.3285 35.3 ppm
Ca
2+
Concentration of Mg
2+ using graph
5.50 ppm Mg
2+
Ca
2+ concentration in CaCO
4.7 ppm
CaCO
3
18.2 ppm Mg
2+
74.3 ppm
3
0.115 ppm
Mg
2+
CaCO
3
59.8 ppm
CaCO
3
20.2 ppm Mg
2+
88.3 ppm
CaCO
3
Mg
2+ concentration in CaCO
3
22.6 ppm
CaCO
3
74.9 ppm
CaCO
3
0.473 ppm
CaCO
3
83.1 ppm
CaCO
3
Table 1.5- Atomic Absorption Total Concentration
(Sample Calculation #10)
Sample
Britta Filter
Sink Water
Poland Springs Bottled Water
Water Fountain
Total Concentration in CaCO
3
27.3 ppm
149.2 ppm
60.3 ppm
171.4 ppm

Krupski 12
Table 1.7- EDTA Titration of Water Sample
(Sample Calculation #3-“Calculated Hardness”)
Sample
Britta Filter
(Sample Calculation #3a-“ Hardness in ppm”
(Sample Calculation #3b-“Hardness in grains/gallon”
Drops
3 drops
Calculated
Hardness
6.00 × 10 −4 𝑀
Hardness in ppm
60.0 ppm
Sink Water
Poland Springs Bottled
Water
Water Fountain
11 drops
3 drops
8 drops
2.20 × 10 −3 𝑀
6.00 × 10 −4 𝑀
1.60 × 10 −3 𝑀
220. ppm
60.0 ppm
160. ppm
Hardness in grains/gallon
3.51 grains/gallon
12.87 grains/gallon
3.51 grains/gallon
9.36 grains/gallon
Table 1.8- EDTA Titration of Water Sample with Softening Power
(Sample Calculation #4)
Sample
Britta Filter
Sink Water
Poland Springs Bottled Water
Water Fountain
Drops
2 drops
9 drops
1 drops
7 drops
Calculated Hardness
4.00 × 10 −4 𝑀
1.80 × 10 −3 𝑀
2.00 × 10 −4 𝑀
1.40 × 10 −3 𝑀
Sample
Britta Filter
Sink Water
Poland Springs
Bottled Water
Water Fountain
Table 1.9- EDTA Titration of Water Sample with Ion Exchange Resin
(“Calculated Hardness--Sample Calculation #5)
Drops
0 drops
2 drops
1 drops
Calculated
Hardness
Effectively 0
4.00 × 10 −4 𝑀
2.00 × 10 −4 𝑀 pH (water sample)
7 (neutral)
7 (neutral)
3 (acidic) pH (after ion exchange)
3 (acidic)
2 (acidic)
1(acidic)
1 drops 2.00 × 10 −4 𝑀 7 (neutral) 3(acidic)

Krupski 13
Discussion:
The initial molarity calculation of the known Ca
2+
concentration using EDTA titration was only 0.0002 off from the actual value marked on the bottle. When both the known Ca
2+
and
Mg
2+
concentration were added during the EDTA titration the calculated value of molarity was practically the same (only 0.0001M less). This makes sense because the concentration of
Ca
2+ and Mg
2+ are both 1.00 × 10 −3 𝑀 and the ratio of each with 2 drops should still be the same.
Our AA results show that the Britta filter is the softest of the all the water samples with a
27.3 ppm (slightly hard) followed by the Poland Springs Bottled Water at 60.3 ppm (moderately hard). There is a large gap between the Poland Springs Bottled Water and the Sink Water which had a calculated water hardness of 149.2 ppm (hard) followed by the water fountain water sample at 171.4 ppm (hard). Some of these results align with my hypothesis. I correctly predicted that the Sink Water and Fountain Water would be the two hardest but I believed that the Poland Springs Bottled Water would be less hard than the Britta filter water. Up until this laboratory exercise, I was not very familiar with how a Britta filter worked and always assumed that Bottled Water went through the most processes and would be the least hard. It is interesting to note that the ion exchange resin resulted in softer water for every sample than the commercial water-softening agent. Knowing that a Britta uses an ion exchange resin, I noticed how effective this process is and realized that may have accounted for the unpredicted softness from the Britta water filter.
The Dissolved Solids experiment showed that the solid residue was greatest in the water fountain sample, aligning with the AA results that it was hardest sample. It should be noted that other solids dissolved in water can contribute to the TDS experiment, like NaCl but would not affect the hardness; thus, the TDS values are related to hardness (as usually water with a large

Krupski 14 amount of dissolved solids tends to be hard as a large portion of the solids are calcium and magnesium), but they are not identical (6). The sink water had the second heaviest white ring
(once again aligning correctly with AA results) followed by the Britta filter and then the Poland
Springs Bottled Water. Although the AA results showed that the Britta filter water sample was the softest, the Poland Springs Bottled Water and Britta Filter water samples both evaporated leaving weak solid white rings and it was difficult to tell which one was heavier.
Our EDTA titration data showed that the sink water was the hardest with 220. ppm (very hard) followed by the water fountain water with 160. ppm (hard) and then the Britta Filter and the Poland Springs Bottled Water both with 60.0 ppm (moderately hard). Although the clear trend that the Britta Filter and Poland Springs Bottled Water are both the softest and the water fountain water and the sink water are the hardest exists in both the EDTA titration and AA results, the EDTA titration showed that the sink water was the hardest while the AA showed that the water fountain water was the hardest. It is interesting to note that the Poland Springs Bottled
Water was measured as 60.0 ppm through EDTA titration and 60.3 ppm through AA, seemingly extremely precise answers. The percent error difference between the EDTA titration and the AA for my sink water sample was 32.18 % (Sample Calculation #11). Probable sources of error that could account for these differences include interference with the EDTA titration as some metal ions interfere by causing fading or indistinct end points or by stoichiometric consumption of
EDTA (1). Also, our 12 well strip for the EDTA titration could have remained a little dirty even though we washed it with distilled water. Furthermore, the drops may have been squeezed at different strengths resulting in different drop sizes. Lastly, suspended colloidal organic matter also may interfere with the end point of the titration (4). It should be noted that this error can be eliminated by the following process: evaporating the sample to dryness on a steam bath and

Krupski 15 heating in a muffle furnace at 550C until the organic matter is completely oxidized. Then, dissolving the residue in 20 mL 1 N hydrochloric acid (HCl), neutralize to pH 7 with 1 N sodium hydroxide (NaOH), and making up to 50mL with distilled water followed by cooling to room temperature (4). However, this process is lengthy and complex and was not performed during our laboratory experience. Possible sources of error for the AA method could be an incorrect calibration; however, since the previous discussed four possible sources of error that relate to the
EDTA titration are much more likely to occur, I believe that the AA is more accurate and precise as it also can measure to more decimal places.
It is also curious to note these calculated values in relevance to other “standard” water hardness levels in the State College Area. The State College Borough Water Authority, wrote that a large majority of tap water is groundwater pumped from wells and natural contains some amounts of magnesium and calcium. Their reported water hardness levels range between 120-
190 mg/l (16). These values correspond to 120-190 ppm which in the AA results, both the sink water (149.2 ppm) and the water fountain water (171.4 ppm) were between. The EDTA titration for the water fountain was in the range (160. ppm) but the EDTA titration for the sink water was not (220. ppm). This gives greater confidence in the AA absorption values as opposed to the
EDTA titration values since the State College Borough Water Authority is legally responsible for providing accurate data and I do not think that the sink water was truly that hard.
Conclusions:
It is clear that bottled water and Britta filtered water have gone through filtration processes causing the water to become less hard. Although hard water does correspond to water quality, many misunderstand its significance and believe it is linked to health risks; however, it is

Krupski 16 not (2). Other containments in water are regulated for health-related reasons, but calcium and magnesium are not. This principle agrees with my hypothesis as well as my prediction that the sink water will be similar in hardness to the water fountain water. However, I predicted that the
Poland Springs Water Bottle would be less hard than the Britta filter, which was not the case.
Also, looking at the multiple probably sources of error by EDTA titration and the fact that the sink water for EDTA titration was not in the range reported by the State College Borough Water
Authority, the AA absorption method was determined to be the more accurate method for determining water hardness.
Sample Calculation Equations Page:
1.) Sample Calculation 1—Concentration of original 10 −3 𝑀 Ca
2+ solution:
𝑀
𝐸𝐷𝑇𝐴
× 𝑉
𝐸𝐷𝑇𝐴
= 𝑀
Ca2+
× 𝑉
Ca2+
(2.00 × 10 −4 𝑀) × (6 𝑑𝑟𝑜𝑝𝑠) = 𝑀
Ca2+
× (1 𝑑𝑟𝑜𝑝)
𝑀
Ca2+
= 1.20 × 10 −3 𝑀
2.) Sample Calculation 2—Concentration of original 10 −3 𝑀 Ca
2+ solution and 10 −3 𝑀 Mg
2+ solution:
𝑀
𝐸𝐷𝑇𝐴
× 𝑉
𝐸𝐷𝑇𝐴
= 𝑀
Ca2+ and Mg2+
× 𝑉
Ca2+ and Mg2+
(2.00 × 10 −4 𝑀) × (11 𝑑𝑟𝑜𝑝𝑠) = 𝑀
Ca2+
× (2 𝑑𝑟𝑜𝑝𝑠)
𝑀
Ca2+ and Mg2+
= 0.0011𝑀
𝑀
Ca2+ and Mg2+
= 1.10 × 10 −3 𝑀
3.) Calculation for water sample hardness in molarity
𝑀
𝐸𝐷𝑇𝐴
× 𝑉
𝐸𝐷𝑇𝐴
= 𝑀
Watersample
× 𝑉
Watersample
(2.00 × 10 −4 𝑀) × (11 𝑑𝑟𝑜𝑝𝑠) = 𝑀
Watersample
× (1 𝑑𝑟𝑜𝑝)
𝑀 watersample
= 2.20 × 10 −3 𝑀

Krupski 17
3a.) Conversion of 𝑀 to ppm:
2.2 × 10 −3 𝑚𝑜𝑙𝑒𝑠 𝐶𝑎𝐶𝑂
1𝐿
3
×
100.0 𝑔 𝐶𝑎𝐶𝑂
3
1 𝑚𝑜𝑙𝑒 𝐶𝑎𝐶𝑂
3
= 220. 𝑝𝑝𝑚
×
1000𝑚𝑔 𝐶𝑎𝐶𝑂
3
1𝑔 𝐶𝑎𝐶𝑂
3
=
220. 𝑚𝑔 𝐶𝑎𝐶𝑂
3
1 𝐿 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
3b.) Conversion of ppm to grain/gallon:
220. 𝑚𝑔 𝐶𝑎𝐶𝑂
3
1 𝐿 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
1 𝑔𝑟𝑎𝑖𝑛
×
64.7 𝑚𝑔
3.785 𝐿
×
1 𝑔𝑎𝑙𝑙𝑜𝑛
= 12.87
𝑔𝑟𝑎𝑖𝑛 𝑔𝑎𝑙𝑙𝑜𝑛
4.) Calculation of water hardness using a Commercial Water-Conditioning Agent
𝑀
𝐸𝐷𝑇𝐴
× 𝑉
𝐸𝐷𝑇𝐴
= 𝑀
Watersample
× 𝑉
Watersample
(2.00 × 10 −4 𝑀) × (9 𝑑𝑟𝑜𝑝𝑠) = 𝑀
Watersample
× (1 𝑑𝑟𝑜𝑝)
𝑀 watersample
= 1.80 × 10 −3 𝑀
5.) Calculation of water hardness using NH3/NH4Cl/MgEDTA buffer
𝑀
𝐸𝐷𝑇𝐴
× 𝑉
𝐸𝐷𝑇𝐴
= 𝑀
Watersample
× 𝑉
Watersample
(2.00 × 10 −4 𝑀) × (2 𝑑𝑟𝑜𝑝𝑠) = 𝑀
Watersample
× (1 𝑑𝑟𝑜𝑝)
𝑀 watersample
= 4.00 × 10 −4 𝑀
6.) Sample Calculation of water hardness using graph of Concentration of Ca
2+ vs. Absorbance.
My Ca 2+ absorbance value = 0.2904 𝑦 = 0.0094𝑥 + 0.0109
𝐴𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒 = 0.0094 (𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐶𝑎 2+ 𝑝𝑝𝑚) + 0.0109
0.2904 = 0.0094 (𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐶𝑎 2+ 𝑝𝑝𝑚) + 0.0109
29.7 𝑝𝑝𝑚 = 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐶𝑎 2+
7.) Conversion of Concentration of Ca
2+ ppm to 𝐶𝐴𝐶𝑂
3 ppm

Krupski 18
29.7 𝑝𝑝𝑚 𝐶𝑎 2+ =
(100𝑔𝐶𝐴𝐶𝑂
3
1 𝑚𝑜𝑙𝑒
40.0𝑔𝐶𝑎 2+
)
1 𝑚𝑜𝑙𝑒
= 74.25 𝑝𝑝𝑚𝐶𝐴𝐶𝑂
3
8.) Calculation of water hardness using graph of Concentration of Mg
2+ vs. Absorbance.
My Mg 2+ absorbance value= 0.2980
𝑦 = 0.0157𝑥 + 0.0118
𝐴𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒 = 0.0157 (𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑀𝑔 2+ 𝑝𝑝𝑚) + 0.0118
0.2980 = 0.0157 (𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑀𝑔 2+ 𝑝𝑝𝑚) + 0.0118
18.2 𝑝𝑝𝑚 = 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑀𝑔 2+
9.) Conversion of Concentration of Mg
2+ ppm to 𝐶𝐴𝐶𝑂
3 ppm
18.2 𝑝𝑝𝑚 𝑀𝑔 2+ =
(100𝑔𝐶𝐴𝐶𝑂
3
1 𝑚𝑜𝑙𝑒
24.3𝑔𝐶𝑎 2+
)
1 𝑚𝑜𝑙𝑒
= 74.9 𝑝𝑝𝑚𝐶𝐴𝐶𝑂
3
10.) Total concentration of CaCO
3
(water hardness):
𝐶𝐴𝐶𝑂
3 ppm (from Ca
2+
(sample calculation #7)+ 𝐶𝐴𝐶𝑂
3 calculation #9) = 74.25 𝑝𝑝𝑚𝐶𝐴𝐶𝑂
3 +
74.9 𝑝𝑝𝑚𝐶𝐴𝐶𝑂
3 ppm (from Mg
= 149.2 𝑝𝑝𝑚 𝐶𝐴𝐶𝑂
3
2+
(sample
11.) Percent Error Calculation between EDTA Titration and AA:
My EDTA titration hardness was 220. Ppm (sample calculation #3a and my AA hardness value was 149.2 ppm (sample calculation #10). Note that this calculation assumed the AA value to be the “actual” value. Even though it is not exact, it has less possible causes of error (See
“probably errors” in Discussion Section).
% 𝐸𝑟𝑟𝑜𝑟 =
|𝐴𝑐𝑡𝑢𝑎𝑙 − 𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙|
×
𝐴𝑐𝑡𝑢𝑎𝑙
|220 − 149.2|
=
|𝐴𝐴 𝐴𝑏𝑠𝑜𝑟𝑏𝑡𝑖𝑜𝑛 − 𝐸𝐷𝑇𝐴 𝑇𝑖𝑡𝑟𝑎𝑡𝑖𝑜𝑛|
× 100% = 32.18%
𝐴𝐴 𝐴𝑏𝑠𝑜𝑟𝑏𝑡𝑖𝑜𝑛
220
× 100%

Krupski 19
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