Chem Lab Report

The Chemistry of Natural WatersJosh Hull11/9/05

Experiment #10Meredith HudakMike HinmanTanner Gokec

Tyler Hall

I. Introduction: Hard water is water that has a high mineral content (water that

contains a low mineral content is said to be soft). This content usually consist

of high levels of metal ions, mainly calcium (Ca2+) and magnesium (Mg2+) in

the form of carbonates1. Other metals as well as bicarbonates and sulfates

may also be included.2 Earlier generations coined the phrase “hard water”

because it made cleaning extremely difficult. Hardness is caused by

compounds of calcium and magnesium, and a variety of other metals. All

freshwater sources of water contain calcium and magnesium in varying

quantities. Water tends to suspend, dissolve, and exchange certain trace

elements and compounds from many objects that it contacts on its travels.3

For example, lime will harden water and peat will soften it.

Total water hardness which includes both Ca2+ and Mg2+ is reported in

parts per million (ppm) of calcium carbonate (CaCO3). Water hardness

usually measures the total concentration of calcium and magnesium, the two

most prevalent divalent metal ions.4 In some geographical locations, iron,

aluminum, and manganese may also be present at elevated levels. Calcium

usually enters the water from either CaCO3, limestone or from mineral

deposits of CaSO4.5 Magnesium predominantly comes from dolomite,

CaMg(CO3)2.6

Temporary hardness pertains to hardness which can be removed by boiling

or by the addition of lime (calcium hydroxide). It is caused by dissolved

calcium bicarbonate in the water. Calcium bicarbonate is less soluble in hot

water than in cold water, so boiling (which promotes the formation of

carbonate) will precipitate calcium carbonate out of the solution, leaving

water that is less hard on cooling.7

On the other end of the spectrum, permanent hardness is mineral content

that cannot be removed by boiling. It is usually caused by the presence of

calcium and magnesium sulfates in the water, which are more soluble as the

temperature rises.

The mixture of minerals dissolved in the water, together with the water’s

acidity or alkalinity, as well as the temperature, will determine the behavior of

the hardness.8 Descriptions of hardness correspond roughly with the ranges of

mineral concentrations:9

Hardness Concentration of Calcium (mg/L Ca)Soft 0-20

Moderately Soft 20-40Slightly Hard 40-60

Moderately Hard 60-80Hard 80-120

Very Hard >120

Water hardness does not present a health hazard, however it can cause

many potentially costly problems. Hard water also causes scaling, which is

the precipitation of minerals to form a rock-hard deposit called lime scale.10

Scale has the potential of clogging pipes and decreasing the life of toilet

flushing units by 70% and water faucets by 40%.11 It may also coat the

insides of tea pots and coffee pots, and clog and destroy hot water heaters.

In the household environment, hard water requires more soap and

synthetic detergents for laundry and washing. It takes half as much soap for

cleaning with soft water. Hard water and soap often combine with one

another to form soap scum which cannot be rinsed off. This scum forms

bathtub rings and unwanted spots on your dishes. Using soap on your body in

hard water can cause the formation of scum which is often referred to as

curd.12 The formation of scum and curd is caused when calcium and

magnesium form insoluble salts with anions.13 This curd remains on the skin

even after rinsing. The curd may then clog pores and coat body hair. This can

serve as the origin for bacterial growth, causing diaper rash, minor skin

irritation and skin that constantly itches.14

In commercial industry, hard water contributes to scaling in boilers,

cooling towers, and other industrial equipment. When hard water is heated or

evaporated, rocklike deposits consisting mainly of calcite crystals form on the

surface of pipes, boiler walls, tubes, and evaporator surfaces.15 Scale is one of

the banes of industry. It blocks jets and tubes, and narrows pipes. The hard

layer interferes with heat transfer in boilers, leading to gross energy

inefficiencies, and can often lead to metal corrosion and structurally

weakness. In these settings, water hardness must be under constant review to

avoid costly breakdowns. Hardness is controlled by the addition of chemicals

and by large scale softening with zeolite resins.

A water softener works on the principle of cation or ion exchange in

which ions of the hardness minerals are exchanged for sodium or potassium

ions.16 The most economical way to soften household water is with an ion

exchange water softener. This unit uses sodium chloride (table salt) to

recharge beads made of ion exchange resin the exchanges hardness minerals

for sodium17. Artificial or natural zeolites can also be used. As the hard water

passes through and around the beads, the hardness minerals attach themselves

to it, dislodging the sodium ions. This process is called ion exchange18.

When the beads or sodium zeolite has no sodium ions left, it is exhausted and

can no longer soften the water. The resin is recharged by flushing with

saltwater. The excess of sodium ions force the hardness ions off the resin

beads. The excess sodium is rinsed away and the resin is ready to start the

process all over again.

According to the US Geologic survey, 85% of US homes have hard

water.19 The softest water occurs in parts of New England, South Atlantic-

Gulf, Pacific Northwest, and Hawaii regions.20 Moderately hard waters are

common in many of the rivers of Tennessee, Great lakes, Pacific Northwest,

and Alaska regions.21 Hard and very hard waters are found in some of the

streams in most of the regions throughout the country22. Hardest waters are

found in the streams of Texas, New Mexico, Kansas, Arizona and Southern

California23.

EDTA titration is used to determine the concentration of divalent cations

(hardness) in water (for example the concentration of calcium and

magnesium).24 1. A known volume of water is taken and the pH is adjusted to

10 by a NH3/NH4 buffer. 2. EBT indicator is added to the solution. At the

high pH the indicator is in the HD2- form, which is blue. 3. If magnesium is

present in the water sample then it will react with the indicator to form a wine

red chelate. Calcium does not react with the indicator. Therefore, at the start

of the titration, the solution is wine red in color. 4. EDTA solution is now

added to the solution from a microburet. It first reacts with calcium and forms

a colorless chelate. As soon as enough EDTA has been added, it begins to

react with the magnesium indicator chelate to produce a MgEDTA chelate.

When the magnesium is removed from the indicator, it returns to its blue

form. 5. The end point of titration is a definite change from a wine red color

to a blue sky color.25

Titration is difficult to do if there is little or no magnesium in the water

sample. If there is no magnesium in the sample, then the color of the solution

at the beginning would be the same at the end of the titration, in other words

there would be no end point. In order to ensure that the sample contains

enough magnesium, it is usually spiked with a solution which contains the

MgEDTA chelate.26

After the titrations were complete in the experiment, the following

equation was used to determine the concentration of the calcium solution.

Moles of EDTA=moles of Ca2+

MEDTAVEDTA=MCa2+VCa

2+

Atomic absorption spectrophotometry (AA) is a technique which is

used to determine metals that are dissolved or suspended in a solution.27

These metals can consist of alkalis, alkaline earth, and even transition metals.

In order for the atom of interest to be excited, the energy of light falling on the

atom must match the energy separation between two electronic energy

levels.28 This principle is used in the operation of AA. Monochromatic light

having the energy corresponding to the change in energy of the atoms of

interest is shined through the sample which is to be analyzed.29 Atoms which

have electronic energy separation will absorb the light. The amount of

absorbance is proportional to the concentration of the metal atoms in the

sample. The Beer-Lambert law is used to calculate the unknown metal

concentration in the sample30.

A typical atomic absorption spectrophotometer functions in a systematic

way. Voltage across the electrodes excites the calcium and magnesium inside

the lamp. When the excited Mg or Ca atoms relax, a monochromatic light is

produced which equals the energy separation of the two electronic levels. The

emitted monochromatic light will then be absorbed by Mg or Ca atoms in the

water sample.31 The liquid water sample is then aspirated into the sample

chamber where it is converted from a liquid to a fine aerosol which is

introduced into a flame. The flame is composed of air-acetylene mixture

which reaches 2300 degrees Celsius. This temperature is capable of

atomizing everything in the liquid sample. The light from the hallow cathode

lamp passes through the flame where the sample is atomized. The light will

only be absorbed if there is a matching energy separation of energy levels.32

A grating in the monochrometer is adjusted so that only the wavelength of

light corresponding to the energy change of the metal of interest is allowed to

pass through a narrow slit. This light then falls on the detector which is a

photomultiplier tube (PMT). Since the metal atoms absorb some light passing

through the flame from the lamp, a decrease in initial signal is detected by the

PMT. This decrease is proportional to the concentration of metal in the

sample.33 The concentration of a metal sample is determined by a calibration

graph that is based on the light absorbance of known concentrations of the

metal of interest.

The goal of this experiment is to determine the hardness of five different

water samples: Aquafina, Dasani, Poland Springs, Evian, and tap water from

Millheim, PA. These values will then be compared to each other as well as to

the state average of hardness for the location in which each bottled water is

produced. After these values are obtained it will be possible to determine

whether each company prefers to sell water which is softer or harder than that

which is found within the state. Millheim town water will be tested due to the

curiosity of how it will compare to the expensive bottled water which is sold

at the store. After all of the samples are tested, the degree of hardness chart

found on page 718 in Chemistry- The Molecular Science, will be used to

classify the samples as soft, slightly hard, moderately hard, hard, or very

hard.34 My hypothesis for this investigation is that the hardness of each

bottled water sample is going to be different than the state value for hardness

of where it is produced. This conclusion has been derived on the basis that

pure water from each state is not just being bottled and sold. Companies use

methods such as chemical and mechanical water softeners, water filters and

magnetic water conditioners to adjust the hardness of water.

The hardness of drinking water does not affect your life as much as the

hardness of the water which is used for household appliances. It is important

to get the water at your own household tested for hardness. The information

that is produced from this test is essential to saving money that will be needed

to repair industrial malfunctions due to water hardness. The addition of a

water softening machine can prevent the clogging of pipes, bath tub rings,

dripping faucets, and the need to replace hot water heaters.

II. Procedure: The procedure for this investigation is found in the PSU

Chemtrek manual. Each water sample is visually examined for particles. If

the sample is not clean it will need to be filtered before the AA process can

take place. Two bulbs must be filled with the sample water (one for Ca

analysis and one for the Mg analysis). Each sample must then be taken to the

instrumental analysis room where the AA process will take place. An

experienced chemist will assist you in operating the AA machine. A series of

buttons are pressed and a thin straw is placed in your water sample. The

machine begins its complicated process (explained in intro) and another

button is pressed which provides you with the absorbance value for your

sample. This process must be done twice, once for calcium concentration and

one for magnesium concentration. Once the absorbance values have been

obtained, a calibration graph of light absorbance vs. metal ion concentration

must be made. Determine the equation of the best fit line for the data. The

absorbance value can then be plugged into the equation in order to produce a

value for the metal ion concentration. This value will then need to be

converted to its equivalent concentration of CaCO3. Finally, the hardness due

to calcium and magnesium must be added together to give a total hardness

value.

A qualitative measurement of the total dissolved solids (TDS) will be

determined. A TDS value is related to hardness, but it is not identical to the

hardness of a sample. Water with a high TDS will most likely be hard. But, if

all of the dissolved solids were NaCl then the sample would have a hardness

of zero. A small piece of aluminum is obtained and placed shiny side up on a

bunsen burner. Two drops of water, one of the designated sample and one of

distilled water are placed on the foil. Allow the water to evaporate and

remove the foil from the burner. The white solids that remain are nonvolatile

salts that were originally in the water sample. This information provides you

with some insight about what your hardness value is comparable to (a lot of

white solid usually means a high hardness).

Divalent Cation Analysis by EDTA titration will take place. This section

requires a quantitative volumetric analysis. One drop of calcium solution,

EBT indicator and buffer is added to each of the wells in a 1x12 well strip.

The strip will now be serially titrated with EDTA solution. The first blue well

is the point where excess EDTA is present. Concentration based on volume

can now be determined using the following equation:

Moles of EDTA=moles of Ca2+

MEDTAVEDTA=MCa2+VCa

2+

The same titration must also be done for magnesium, the sample of interest,

water which contains a water conditioning agent, and water which has had

divalent cation removal by ion exchange.

III. Results:

Fig. 1Calibration graph of light absorbance vs. metal ion concentration for Ca

Absorbance vs. Concentration for Cay = 0.018x + 0.017300.10.20.30.40.50.60.70.80.910.0020.0040.0060.00Concentration (ppm)

Abs

orba

nce

(nm

)

Fig. 2Calibration graph of light absorbance vs. metal ion concentration for Mg

Calibration graphs were derived from data supplied by the instrument operator. Known

absorbance values were graphed vs. known concentration values. A best fit line supplied

an equation which will be used in order to determine the concentration of the test sample.

Absorbance vs. Concentration for Mgy = 0.0152x + 0.003500.050.10.150.20.250.30.350.40.450.50.0010.0020.0030.0040.00Concentration (ppm)

Abso

rban

ce (n

m)

Fig. 3Chart of Mg/Ca hardness determined by AA analysis (best fit line)

Water type Mg2+ hardness (ppm) Ca2+ hardness (ppm)

Millheim tap water 5.88 30

Evian 25.7 42.35

Dasani .656 4.63

Poland Springs 1.06 3.15

Aquafina 9.3 9.13

The equation that was produced by the calibration curve was used to determine thehardness values in Fig. 3.

Fig. 4Chart of concentration of CaCO3

AA analysis

Water type Mg2+ CaCO3 concentration

(ppm)

Ca2+ CaCO3 concentration

(ppm)

Millheim tap water 23.87 75

Evian 105.76 105.88

Dasani 2.67 11.6

Poland Springs 4.36 7.875

Aquafina 38.27 22.825

The hardness values in Fig. 3 were converted to CaCO3 concentration values in Fig. 4.This method of determination will be compared to the EDTA method.

Fig. 5Chart of hardnessEDTA analysis

Water type Hardness (ppm) Hardness

(grains/gal)

Millheim tap water 120 7.0

Evian 120 7.0

Dasani 0 0

Poland Springs 4.21 4.68

Aquafina 20 1.17

A series of titrations where conducted in order to obtain the hardness of the sample waters.This method of determination will be compared to the AA analysis method.

Fig. 6Chart of Total Hardness Value (THV)

AA analysis

Water type THV (ppm)

Millheim tap water 98.8

Evian 211.64

Dasani 14.27

Poland Springs 12.24

Aquafina 61.10

The THV was determined by adding both the concentration of calcium and magnesiumtogether. These values will then be compared to the THV determined by EDTA analysis.

Fig. 7Chart of Total Hardness Value (THV)

EDTA analysis

Water type THV (ppm)

Millheim tap water 120

Evian 120

Dasani 0

Poland Springs 4.21

Aquafina 20

The THV was determined by adding both the concentration of calcium and magnesiumtogether. These values will then be compared to the THV determined by AA analysis.

Fig. 8Classification of Water Hardness

Hardness Concentration of Calcium (mg/L Ca)Soft 0-20

Moderately Soft 20-40Slightly Hard 40-60

Moderately Hard 60-80Hard 80-120

Very Hard >120

This chart will be used to classify the hardness due to concentration of calcium for the fivedifferent samples.

Fig. 9Chart of Average Water Hardness for Various States/Countries

State/Country and type of water Hardness due to Ca2+ CaCO3

concentration(ppm)

Maine (Poland Springs) 9

New York (Aquafina) 65

Pennsylvania (Millheim tap water) 122

France (Evian) 130

Vermont (Dasani) 59

A comparison will be made between the hardness values of the sample waters and thestate in which they are produced in based on the information presented in Fig. 9.

Fig. 10Classification of Hardness

Water Type Classification of HardnessPoland Springs Soft

Aquafina Moderately SoftMillheim tap water Moderately Hard

Evian HardDasani Soft

Sample Calculations:

1. Determination of Ca2+ and Mg2+ hardness by best fit line (absorbance value to ppm)

Ca2+ y=.018x+.0173 .5562=.018x+.0173

.5389=.018x x=29.93 ppm

Mg2+ y=.0152x+.0035 .0771=.0152x+.0035

.0736=.0125x x=5.88 ppm

2. Converting a metal ion concentration in ppm, to a hardness value in ppm

Ca2+ ppm Ca2+ x[100g CaCO3 per mole/40.0 g Ca2+ per mole] 30x[100g CaCO3 per mole/40.0 g Ca2+ per mole]=

75 ppm CaCO3=75 ppm hardness

Mg2+ ppm Mg2+ x[100g CaCO3 per mole/24.3 g Mg2+ per mole] 5.88x[100g CaCO3 per mole/24.3 g Ca2+ per mole]=

23.87 ppm CaCO3=23.87 ppm hardness

3. Calculation of Total Hardness Value

AA Analysis Total hardness value=Ca2+ ppm+Mg2+ ppm Total hardness value=75+23.8

Total hardness value=98.8ppm Ca2+ and Mg2+

4. Calculation of Hardness in molarity

EDTA Analysis MEDTAVEDTA=MSAMPLEVSAMPLE

(2.0x10-4)(6)= MSAMPLE(1) MSAMPLE=1.2x10-3 M

5. Converting a molar concentration of divalent cations into a hardness value in ppm

EDTA Analysis Hardness=1.2x10-3 mol CaCO3/ 1 liter Hardness=(1.2x10-3 mol CaCO3/ 1 liter) x (100g CaCO3/ 1 mol CaCO3) x (1000mg CaCO3/ 1 g CaCO3) Hardness= 120mg/ liter Hardness=120 mg CaCO3/ 1000g H20 Now: 1mg CaCO3/1000g H20 Therefore: 120mg CaCO3/ 1000g H20= 120 ppm hardness

6. Converting ppm value to grains/gallon

EDTA Analysis 1 grain=64.7 mg1 gallon=3.785L

1 grain CaCO3/gal H20= 17.1ppm 120ppm x (1grain/gal)/ 17.1 ppm= 7.0 grains per gallon

IV. Discussion: At the conclusion of the experiment, all goals were met. Water samples

from five different sources: Aquafina, Dasani, Poland Springs, Evian, and tap water from

Millheim, were successfully analyzed and a hardness value was produced for each. Fig 4

shows the break down of Mg2+ CaCO3 concentration and Ca2+ CaCO3 concentration in

parts per million for each sample of water determined by AA analysis. Referring to the

Mg2+ CaCO3 concentration, Evian water produced the highest hardness value of

105.76ppm, Aquafina yielded 38.27ppm, Millheim tap water 23.87ppm, Poland Springs

4.36ppm and Dasani was the softest at 2.67ppm. Analyzing the Ca2+ CaCO3

concentration, Evian once again produced the highest hardness value of 105.88ppm,

Millheim tap water followed with 75ppm, Aquafina 22.825, Dasani 11.6ppm and Poland

Springs was the softest at 7.875ppm. All of the bottled water samples seem to contain a

balance between Ca2+ CaCO3 concentration and Mg2+ CaCO3 concentration. The largest

difference between both concentrations is 15.445ppm. This difference was produced from

Aquafina water. Millheim tap water did not contain a balance between the two

concentrations. The concentration difference was 51.13ppm. This may be due to the fact

that tap water is treated in a different manner than bottled water. Unlike the bottled water

companies, the Millheim water treatment center does not try to produce a balance between

calcium and magnesium concentrations.

In order to obtain a reasonable comparison between the water samples, the total

hardness value determined by AA analysis must be reviewed. Fig. 6 categorizes the THV

for each type of water. Out of five water samples, Evian yielded the highest total hardness

value of 211.64ppm, Millheim tap water was second with 98.8ppm, Aquafina 61.10ppm,

Dasani 14.67ppm, and Poland Springs was the softest at 12.24ppm.

With the AA determination of Ca2+ CaCO3 concentration in each sample, a

comparison between the state averages of Ca2+ CaCO3 concentration in the state in which

the bottled water was produced can be made with the AA value. This comparison is being

made in order to determine whether the bottled water companies prefer to produce water

higher or lower than the state average of Ca2+ CaCO3 concentration. Fig. 9 shows the

average calcium carbonate concentration for each state. Of the five water samples tested,

all of them contained a hardness value less than the state averaged of where they are

produced. This provides evidence that the bottled water manufactures prefer to sell their

products lower than the state average. This data also suggest that the bottled water

companies are not simply bottling tap water and selling it. Methods such as chemical and

mechanical water softeners, water filters, and magnetic water conditioners are being used

to create softer water for sale. The fact that Millheim tap water is below the state average

simply means that the Millheim region produces water slightly softer than the state

average. The difference in hardness was only 47ppm.

Fig. 10 was used to classify the hardness of the water samples by concentration of

calcium. Poland Springs and Dasani both fell under the category of soft. Aquafina was

moderately soft, Millheim tap water was moderately hard, and Evian was ranked as hard.

The hypothesis for this investigation was experimentally proven to be correct. The

hardness of each water sample was different than the state average value for hardness for

the state in which it was produced. In fact, the hardness value for each sample was less

than the state averages, once again supporting the idea that manufactures are using

methods such as: chemical and mechanical water softeners, water filters, and magnetic

water conditioners to produce softer water.

EDTA titration and AA analysis were used to determine the hardness of the water

samples. After reviewing data, AA analysis proved to be the more accurate of the two

methods. The AA machine has been calibrated and fine tuned to produce precise as well

as accurate information. EDTA titration is only precise to one drop due to the fact that

half and quarter drops of titration solution can not be produced. The use of AA analysis

also eliminates a large portion of human error that could occur while performing

calculations like those that are required for EDTA. Human error could occur while

graphing the calibration curve and converting the absorbance value to concentration.

However, this process only counts for a portion of the calculation. The absorbance value

produced by the AA machine is not affected in any way by calculations that contain

human error. The entire EDTA process requires human computations. This fact allows

for a large margin of error due to mistakes made by the chemist.

Due to the possibility of human error, all EDTA values were reviewed. After

comparing THV for AA analysis to EDTA titration, it was determined that the

calculations for EDTA must be repeated for all bottled water samples. Referring to Fig. 6

and Fig. 7, it is obvious that the values do not agree with each other. For instance,

Millheim tap water produced a THV of 98.8ppm (AA analysis) and 120ppm (EDTA).

This two values are reasonable due to the fact that the calculations were repeated several

times. On the other hand, Evian water yielded a THV of 211.64ppm (AA analysis) and

120ppm (EDTA). Duet to the fact that the EDTA values of Millheim tap water and Evian

water are the same and the AA analysis determination is different, an error was obviously

made. Due to the fact that the other EDTA values for the bottled waters don’t agree with

the data, the EDTA values were not taken into consideration when comparing the hardness

values of the water samples. For better results, EDTA titration must be preformed again.

Referring to fig. 7, it may appear as though an error occurred while calculating the

THV for Aquafina water while using the EDTA method. This assumption is incorrect.

Due to very low calcium and magnesium concentrations in Aquafina water, the EDTA

method is insufficient when trying to determine the hardness value.

V. Conclusion: The hardness values for Aquafina, Dasani, Poland Springs, Evian, and tap

water from Millheim, PA were successfully determined. After comparing these values to

the state average values, it was concluded that they all fell below the average state

hardness values. This suggest that water manufactures are using methods to soften the

water before it is sold. In conjunction, these manufactures prefer to sell the water at a

hardness below the state average. The hypothesis for this investigation stated that: the

hardness of each bottled water sample is going to be different than the state value for

hardness of where it is produced. Data produced by this experiment supported and proved

the hypothesis to be correct. However, for a better comparison between AA analysis and

EDTA titration, all EDTA titrations should be repeated due to human error.

VII. References:

1. Water Treatment Methods. http://www.hardwater.org/water_treatment.html. (Oct. 22,

2005).

2. Water Hardness.

www.chemistry.wustl.edu/~edudev/LabTutorial/Water/FreshWater/hardness.html. (Nov.

1, 2005).

3. Explanation of Water Hardness. http://water.usgs.gov/owq/Explanation.html. (Oct 28,

2005)

4. Leeden, Frits van der; Troise, Fred L.; Todd, David Keith The Water Encyclopedia.

Lewis Publishers, Second Edition: Chelsea, MI, 1990 pages 449-453.

5. Moore, John W.; Stanitski, Conrad L.; Jurs, Peter C. Chemistry-The molecular science.

Harcourt College Publishers, First Edition: Philadelphia, 2002, page 718.

6. Thompson S. PSU Chemtrek 2005-06, Haydem McNeil Publishing pages 10-15 - 10-

22.

7. Chem 14 Student packet, section 101-106, Fall 2005, Joseph T. Keiser. pages 49-54.

8. Mike Hinman, Chem 14, Lab Notebook, pg. 17

9. Meredith Hudak, Chem 14, Lab Notebook, pgs. 37-40

10. Tanner Gokec, Chem 14, Lab Notebook, pg. 30

11. Tyler Hall, Chem 14, Lab Notebook, pgs. 27-29

12. Holt, Jack. Water Properties. W.W. Norton and Co. Publishing, First Edition: NewYork, NY, 1998, pages 38-45.

Endnotes to references

1. http://water.usgs.gov/owq/Explanation.html

2. Ibid

3. Ibid

4. www.chemistry.wustl.edu/~edudev/LabTutorial/Water/FreshWater/hardness.html

5. Ibid

6. Ibid

7. Ibid

8. Ibid

9. http://water.usgs.gov/owq/Explanation.html

10. Ibid

11. Water Properties

12. Ibid

13. Ibid

14.. http://www.hardwater.org/water_treatment.html

15. http://water.usgs.gov/owq/Explanation.html

16. http://www.hardwater.org/water_treatment.html

17. Ibid

18. Ibid

19. Water Encyclopedia

20. Ibid

21. Ibid

22. Ibid

23. Water Encyclopedia

24. Water Properties

25. Steps 1-5 PSU CHEMTREK

26. Ibid

27. Ibid

28. Ibid

29. Ibid

30. Ibid

31. Ibid

32. Ibid

33. Ibid

34. Chemistry-The molecular Science