A Study of the Hardness of
Waters Found in State College
KERRICK JOHNSTONBAUGH
Team Members: James Jones, Michael Jayson | Chem 111 – 106, TA: Matt Fares | November 8, 2015
Introduction
Water hardness is a measure of the concentrations of cations with a +2 charge that are
dissolved in a water sample. These +2 cations we will call divalent cations. The two primary divalent
cations present in hard water are magnesium (Mg 2+) and calcium (Ca2+). Hard water has a high
concentration of divalent cations, and soft a low.
Water hardness is of interest for a variety of reasons. Hard water brings with it both pros
and cons, depending on what the intended use of the water is. Drinking hard water increases the
level of magnesium and calcium in one’s diet. Calcium is used by the body to create and maintain
strong bones and teeth, and low levels of calcium may cause osteoporosis, especially in older
adults.1 Calcium is also necessary for the proper functioning of the heart, nerves and muscles.
Magnesium is needed by every organ in the body, and, like calcium, it partly makes up teeth and
bones.2 Magnesium is important to the generation of energy, and it helps to regulate the levels of
other minerals and vitamins in the body. Magnesium is needed by every organ in the body. Both
magnesium and calcium may enhance treatment for high blood pressure, and magnesium
specifically is effective in the treatment of asthma, depression, diabetes, fibromyalgia and more. 2
Alternatively, cons of hard water include the formation of scum when used with soap, and
the formation of scale in pipes and other equipment that deal with the water. Scale is a solid
deposit that forms when hard water is heated or evaporated, and over time it constricts or blocks
pipes and lowers efficiency.3 Scale is very difficult and expensive to remove. For these reasons, it is
useful for industries to determine the hardness of the water which they use, and treat it if
necessary. Clothes washed in hard water require more soap and tend to come out less clean.4
Water can be softened through the use of cation exchange resin.3 The resin that is used
contains cations with a 1+ charge that are exchanged for divalent cations in the water.
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In this report three different samples of water will be discussed by comparing their levels of
hardness as determined by two different methods. The hardness of each sample was measured by
both EDTA titration and by Atomic Absorption Spectrophotometry.
EDTA titration is a kind of serial titration that can be used to measure the concentration of
divalent cations in a sample of water. First, an indicator and a buffer (EBT and NH 3/NH4l/MgEDTA
respectively) are added to the water sample. Then the resulting solution is serially titrated with and
EDTA solution of known concentration. A serial titration can be described as a process in which the
concentration of one solution can be determined by incrementally adding one drop of a solution of
known concentration, until a change in color occurs. The number of drops of the solution of known
concentration that were required to induce the color change can then be used to calculate the
concentration of the unknown solution.
Atomic Absorption Spectrophotometry (AA) is an alternative way to measure the
concentration of specific elements in a solution by using light. Atoms of the same type have
discrete energy levels where their electrons can exist, and when light that has energy equal to the
difference in these energy levels is shined on one of these atoms, the light is absorbed and used to
excite an electron from a lower to a higher energy level. AA takes advantage of this fact, and shines
light of a specific wavelength through a flame that contains the solution that is being measured.
The AA measures the intensity of the light after it passes through the solution and this
measurement can be used to determine the concentration of one specific atom in a solution. The
concentration of only one atom can be tested at a time, so different measurements for Ca2+ and
Mg2+ were made.
This paper analyzes and compares the hardness of water that is available to residents of
State College, PA. The samples analyzed are: Aquafina brand bottled water, tap water from
Greenberg Ice Pavilion, and water from the Alumni Pond on the Penn State campus.
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Sources
http://water.usgs.gov/edu/hardness.html
http://www.chemistry.wustl.edu/~edudev/LabTutorials/Water/FreshWater/hardness.html
2. https://umm.edu/health/medical/altmed/supplement/magnesium
1.
https://umm.edu/health/medical/altmed/supplement/calcium
2.
D
3.
Chemtrek
4.
http://aces.nmsu.edu/pubs/_c/C503/
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