Ben Torres 11/13/12Chem 111 Section103 Mike Shadeck

Experiment 10The Chemistry of Natural

Waters

Ben TorresAlicia White

Robert WertzMatt Wertman

INTRODUCTION

Water hardness is a term often used to define how many ions can be found in a

sample of water being tested1. The ions most often looked at are Calcium and

Magnesium. The higher the concentration of the Ca2+ and Mg2+ ions in the water the

higher the hardness is1. On the contrary, if water has a low concentration of these two

ions it is labeled “soft”. The units to measure the hardness of water are as follows:

molarity (M), parts per million (ppm), mg/L (which is equal to ppm), and grains per

gallon. Ranges for determining if water is hard or soft have been established and are3:

Mg/L Classification

Less than 17.1 Soft

17.1-60 Slightly Hard

60-120 Moderately Hard

120-180 Hard

Above 180 Very Hard

The quantity of these ions in the water is important in its use as both drinking water and

industrial water. It’s important to study water hardness for many reasons but one major

one is that studies show that higher levels of these two ions have been shown to reduce

the chance of having diseases like cardiovascular and cerebrovascular1.

The two major techniques used for determining the hardness of water are EDTA

titration and Atomic Absorption Spectrophotometry2. EDTA titration analysis uses EBT

indicator (eriochrome black) and the water samples together. When added together

magnesium reacts with the EBT and forms a wine red color2. Next the EDTA solution is

added in an increasing interval to the mixed solutions of the water sample and EBT

indicator. The combination of EDTA, EBT, and magnesium ions react all together and

turn the solution blue2. EDTA is successful when magnesium ions are present in the

water sample and are chelated when EBT is added.

The second process used is Atomic Absorption Spectrophotometry (AA). The

basis for AA is the Beer-Lambert law. The Beer-Lambert law relates the absorption of

light to the properties of the material through which the light is travelling. AA

spectrophotometers shine a monochromatic light through a given atom and measure the

amount of ions present in the water in this case. The AA spectrophotometer converts the

water into an aerosol by heating it up via flame2. Then the spectrophotometer shoots a

light through the flame where the sample is then atomized. The light will only be

absorbed if there is a matching energy separation of electronic energy levels2. This

energy separation or wavelength is specific to either calcium or magnesium. Then a

computer in the AA spectrophotometer calculates the absorbance values of the Ca2+ and

Mg2+ ions in the water.

These two techniques are different but both useful. EDTA can analyze the water

and all the cations present. EDTA is flawed in the fact that it cannot measure the separate

the amounts of the ions. Thankfully AA spectrophotometry can accurately calculate the

absorbance values of both the calcium and magnesium ions present.

Due to the need to soften water different processes have arose. Some examples of

these softening techniques are the addition of lime and soda, which precipitates the

magnesium and calcium4,5. Other techniques are ion exchange, which is when sodium

ions replace the ions in the water4. The water passes through a chamber containing resin

beads and the sodium ions switch places with the calcium and magnesium4.

For our experiment my group tested water from four different places on and off

the Pennsylvania State University campus. My sample came from a water fountain in the

Simmons residence hall. Alicia’s sample came from her off campus apartment sink7.

Bobby’s sample came from the showers in the East residence halls9. Matt’s sample came

from a puddle next to a sidewalk on the campus8. My hypothesis will be that Matt’s

water will be the hardest. I believe this to be true because the water will have absorbed

calcium and magnesium from the earth and thus it will have higher amounts of both these

ions. I expect the second hardest to be Alicia’s water because her sink overtime can

develop calcium and magnesium buildups on it and they make the water passing through

it harder. Finally expect my sample to be the next hardest closely followed by Bobby’s.

My water is drinking water and is made intentionally hard to eliminate some

contaminants in it. Bobby’s showerhead water is not drinking water but I expect that it

comes from a similar, if not the same, source as mine.

PROCEDURE

Each member of the group preformed their own experiments on their own water

samples. The procedure for this experiment came from PSU version of Chemtrek2. All

group members preformed the same steps.

We started by testing our water samples using the AA spectrophotometer. We

filled up two pipets with our water samples that we had diluted with a 1:1 ratio of

distilled water to our water sample. We then brought our samples to the machines where

we placed a tube into our samples, which turned the water into an aerosol. Then flame

heats up the aerosol. This process was preformed twice because there was a machine that

calculated the absorbance values

First, a 1inch x 1inch aluminum foil square was cut out and one drop of distilled

water, undistilled sample water, and 1x10-3 M Ca2+ were all dropped on the aluminum

foil2. Then the residue of the total dissolved solids was observed and recorded. Then

EDTA titration was preformed on the water samples. The water samples were organized

in a 12-well strip provided. One drop of the water samples was placed in each well of the

12-well strip. Then a drop of the EBT indicator and one drop of NH3/NH4Cl/MgEDTA

buffer was added in each well. Next serial titration was preformed with 2x10 -4 EDTA.

Once all the Ca2+ and Mg2+ reacted with the EDTA the wells went from the color pink the

color blue2. The well used to find the total ion concentration was the well before the first

blue well2.

The final steps of our experiment were to attempt to make our water softer using

two techniques. The first technique we used was water softening with a commercial

water-conditioning agent. Our water sample was mixed with 20mg of the softening

agent. The pH of the water was recorded before and after this occurred. The second

softening technique used was divalent cation removal by ion exchange. This time we

took our water samples and mixed them with some cation exchange resin. We shook the

vial and mixed the two let them sit then removed the supernatant liquid using a pipet.

Once again the pH of the water was tested before and after the process.

RESULTS

TABLE 1. Observations Of TDS residue after water evaporation from one-drop

samples

Sample Observation

A. Distilled Water No residue

B. 1x10-3 M CaCl2 Reference Faint ring

C. Simmons Water Fountain6 Heavier White residue ring compared to

reference

D. Apartment Sink7 Similar to reference

E. Puddle8 Heavier ring compared to reference

F. Shower9 Similar to reference

Table 2: EDTA results from water samples

Concentration (M) Concentration

(ppm)

Grains per Gallon

Simmons Water

fountain6

2.8x10-3 M 280 ppm 16.37

Apartment Sink7 2.0x10-3 M 200 ppm 11.69

Puddle8 4.0x10-3 M 400 ppm 23.4

Shower9 3.2x10-3 M 320 ppm 18.7

Equation1: Calculation of molarity

MEDTAVEDTA=MSAMPLEVSAMPLE

Calculations with my numbers

(2.0x10-4)(7 Drops)=MSAMPLE(1 Drop)

MSAMPLE = 1.4x10-3 M

Then multiply times two because of dilution ratio

2.8x10-3 M

Equation 2: Calculation of parts per million (ppm) = mg CaCO3/L of solution

Moles Divalent Cations X 100.0 g CaCO3 X 1000 mg CaCO3 = mg CaCO3

1 Liter of Solution 1 Mole CaCO3 1 g CaCO3 1 Liter of Solution

Simmons Water Fountain6

1.4x10 -3 M X 100.0 g CaCO3 X 1000mg CaCO3 = 140 mg CaCO3

1 Liter of Solution 1 Mole CaCO3 1 g CaCO3 1 Liter of Solution

140ppm*

Equation 3: Calculations of Grains per Gallon

Ppm of sample X 1 grain per gallon = grains/gallon

17.1 ppm

Simmons Water Fountain6

140 ppm X 1 grain per gallon = 8.18 grains/gallon

17.1 ppm * need to multiply by two because of diluting ratio 1:1

Table 3: AA standards of Calcium and Magnesium, concentrations, and check standards6

Concentration (ppm) Absorbance Value

Ca @ 422.76 nm

Mg @ 202.5 nm

Check Standard

(ppm)

Calcium

Magnesium

0 0 01.000 .00631 1.075.00 .04670 4.9210.00 .08487 9.8825.00 .20106 24.6450.00 .38054 50.040 0 01.000 .01909 0.895.00 .09535 5.4110.00 .17313 9.3225.00 .36944 24.9850.00 .45017 30.70

Both the graphs above show a calibration equation that has been derived from the

line of best fit on each graph6. The calibration equations are used to calculate the

concentrations of both the ions. Table 3 shows all the data that was used to create the

axis and points for the graph, which led to the creation of the calibration equation.

Table 4: AA Absorbance and Hardness (ppm) results

Absorbance Value

(nm)

Concentration

(ppm)

Hardness (ppm)

Simmons Water

Fountain6

Total Hardness-

325.32

Ca2+ .2172 14.08 63.54

Mg2+ .2294 31.77 261.78

Apartment Sink7 Total Hardness-

245.45

Ca2+ .2489 31.28 NA

Mg2+ .1728 10.82 NA

Puddle8 Total Hardness-

282.4

Ca2+ .2406 30.72 153.6

Mg2+ .2545 15.63 128.64

Shower Water9 Total Hardness-

294.76

Ca2+ NA NA NA

Mg2+ NA NA NA

*NA- Either the values were not given to me or I was not given enough

information to calculate them myself

Equation 4: Calculation of Concentration (ppm) from Absorbance Value Using

Calibration Equation

X= concentration

Y = Absorbance Value

Calibration equation Ca2+: y = .014x + .02

Calibration equation Mg2+: y = .007x + .007

Ca: .2172 = .014x + .02 x = 14.08

Mg: .2294 = .007x + .007 x = 31.77

Equation 5: Calculation of equivalent concentration

Ppm Ca2+ x 100g CaCO3/mol = ppm CaCO3 (hardness)

40.0 g Ca2+/mol

Ppm Mg2+ x 100g CaCO3/mole = ppm CaCO3 (hardness)

23.4 g Mg2+/mole

Ca2+: 14.08 x 100g CaCO3/mole = 35.2 ppm *multiply by 2 when finding total

hardness

40.0 g Ca2+/mole

Mg2+: 31.77 x 100g CaCO3/mole = 130.89 *multiply by 2 when finding total

hardness

23.4 g Mg2+/mole

35.2(2) + 130.89(2) = 325.32 ppm

Table 5: EDTA results of softened water samples

Commercial

Softener (ppm)

Resin Beads (ppm) pH of water treated

with resin

Simmons water

fountain 6

280 20 5

Apartment water7 240 80 NA

Puddle8 280 40 NA

Shower Water9 280 20 NA

DISCUSSION

First we will start out by looking at table 1. The results from the TDS analysis

suggest that the puddle and the Simmons drinking water will have the highest water

hardness levels then followed by the apartment water and the shower water. Table 2

helps support this point by showing that the puddle had the highest grain per gallons at

23.4 then followed by the shower at 18.7, then the Simmons water fountain close behind

at 16.37 and finally the apartment sink at 11. 69.

Table 4 switches things up slightly and has the Simmons water fountain overall

having the highest total hardness; Although it had the lowest Ca2+ hardness. One can see

that the Mg2+ levels were very high in the Simmons water fountain.

My hypothesis was correct in some aspects but incorrect in others. Overall I

guessed the wrong order of hardness. But some of my predictions did end up being

slightly true. I was right about the puddle gathering up calcium and magnesium because

you can see that their hardness’s are very close to each other. I was also close in my

prediction that the sample from the water fountain and the sample from the shower would

be similar. There was only a difference of about 25 ppm, which is only a difference in in

well in the 12 well tray6. The two samples with the highest hardness values ended up

being the Simmons Hall water fountain and the East Halls showers. Now that I think

about it, it makes sense because both the shower and the water fountain are used

throughout the day everyday, which would account for a high amount of buildup, which

would contribute to the hardness10.

Next we have the results from the commercial water softener. The water softener

worked for all the samples but some more than others. For both the puddle and the

apartment sink the hardness with the softener compared to with out the softener was

barely different. The apartment sinks hardness only dropped 5.45 ppm while the puddle

only dropped 2.4 ppm. On the other hand the softener worked decently for the shower

water dropping its hardness 14.76 ppm. The water softener worked best on the water

fountain water though dropping it 45.32 ppm. The varied results could be two where the

ideal range for ppm is. Three of the four members of the group got 280 as their ppm for

after the softener was used. The fluctuation in the effectiveness of the softener could be a

result of the softener attempting to reach an ideal hardness.

Unfortunately Pennsylvania State University does not keep records of the water

hardness of its shower water and drinking water and neither does the apartment complex

that we received the sink water from. Also it is hard to tell what the actual hardness of

the puddle water is because so many factors go into how much Ca2+ and Mg2+ got into the

puddle water in that given amount of time. Of course without any of the actual values of

hardness known it is hard to say what we did wrong if anything, although there is always

room for error. Possible errors could have come from not being able to accurately

pinpoint where the titration should have ended. In EDTA titration you are going of color

change and where you believe the color changes enough to be considered the turning

point. If you are off by a single well than your results will vary in all your calculations

from there on because you are using an incorrect value. Another possible error could

have come during the softener process. There were some significant changes in the

hardness while there were some that were barely noticeable. This could be a result of

everyone doing the experiment by themselves and each person using a slightly different

amount of softener. As all chemists know, even a slight difference in mass can throw off

you results. In the end, of the two methods we used AA spectrophotometry is the more

precise technique. In almost every scenario a machine will work better in determining

something than the human judgment. AA spectrophotometry is also much faster and

more efficient.

CONCLUSION

Most of the water samples we took were all from the same area and this might be

one of the main factors that explain why all the measurements of hardness we got was

similar. After all the results were in the hardest of all the waters was the Simmons Hall

water fountain (325.52ppm) followed by the East Halls shower water (294.76ppm), then

the puddle (282.4ppm) and finally the apartment sink water (245.45ppm) The results

make sense as one would expect the shower water and water fountain water to be close

because they both come from Penn State’s water source. All the samples ended up being

above 180ppm, which made them very hard. This also makes sense because as

previously stated research has shown drinking hard water is indeed better for you than

drinking soft water.

REFERENCES

1. Koçak N, Güleç M, Tekbaş ÖF. [Water Hardness Level and It’s Health Effects].

www.scopemed.org/?mno=1566 [Access: November 7, 2012].

Turkish. doi:10.5455/pmb.20101124053432

2. PSU Chemtrek; Stephen Thompson, Ed.; Prentice Hall: Englewood, NJ, 2012-2013

version Chapter 10

3. Fairfax County Water Authority. "Explanation of Water Hardness." NAV. Web. Nov

7. <http://www.fcwa.org/water/hardness.htm>

4 Casiday, Rachel. "Water Hardness." Water Hardness. Washington University, 1998.

Web. 7 Nov. 2012.

<http://www.chemistry.wustl.edu/~edudev/LabTutorials/Water/FreshWater/

hardness.html>.

5. Brown, Lemay, and Buster. Chemistry: the Central Science, 7th ed. Upper Saddle

River, NJ: Prentice Hall, 1997. p. 681-3

6. Torres, Ben. Chem 111 Lab Notebook Pg 32-36

7. White, Alicia. Chem 111 Lab Notebook Pg 32-36

8. Wertman, Matt. Chem 111 Lab Notebook Exp 10 Notes

9 Wertz, Bobby. Chem 111 Lab Notebook Exp 10 Notes

10. "Hardness in Your Drinking Water." Water Systems Council. N.p., July 2004. Web. 6 Nov. 2012. <http://www.watersystemscouncil.org/VAiWebDocs/WSCDocs/1683274HARDNESS.PDF>.

11. "Science Notes/Chemistry." Lexis Nexis. The Buffalo News, 2011. Web. 7 Nov. 2012. <http://www.lexisnexis.com.ezaccess.libraries.psu.edu/hottopics/lnacademic/?verb=sr&csi=8391&sr=HLEAD(Science+notes+%2F+Chemistry)+and+date+is+November+13%2C+2011>.