Minnesota State University

Measuring Alkalinity, Acidity, and Hardness to determine Water Quality

13Fall

Written by: Raquel Collison

ABSTRACT – Alkalinity, acidity, and hardness have been classified as three important factors affecting Minnesota State University’s tap water quality. The various experiments conducted to test the stated factors were performed using a burette and cold tap water and three trials were noted to represent each qualification standard. The results revealed that the water properties (in respective order) stated that the water had a high alkalinity (29.33 ppm of CaCO3), lower acidity (8 ppm of CaCO3), and was classified to have a hardness value of 210 (ppm of CaCO3). From this information conclusions were made regarding the low sensitivity of the sample water supply towards additional acid (such as polluted rain), representing its fertility in a natural system, as well as be classified with a hardness rating of “hard,” which signifies a greater dissolved metal content than other chemically treated waters. This information then can be better understood as means of classification of Mankato’s water supply and as a basis for any treatment options that may be required.

Water quality control measures have been taken across the United States for

concerns relative to both the natural environment and human use. These concerns

are almost always symbiotic, representative of the need for consistent monitoring of

the three largest factors that contribute to water quality: alkalinity, acidity, and

hardness. In this experiment, we will investigate the three factors and determine an

average for each, so that we can better understand the makeup and chemical

balance of Mankato State University’s tap water system in order to make valid

conclusions relative to quality as dictated by the various ranking systems proposed.

The classification guidelines are defined as follows:

Alkalinity represents the ability of water molecules to accept H+ protons. In

short, it signifies the capacity of water to neutralize acids that may stem from acid

rain, for example. A high alkalinity means that a lake is fertile and buffered, in other

words, its pH does change enough to affect the aquatic animals, and so life thrives in

such a water body with a high alkalinity.

Acidity represents the ability of water molecules to neutralize OH- molecules,

the exact opposite of alkalinity. Acidic water typically has a high CO2 concentration,

which in usually high levels can lead to eutrophication of a water body.

Eutrophication is the resulting death of a lake caused by the oxygen – depleting

process of dead algae breakdown by microbes (“The Carbon Dioxide Greenhouse

Effect,” 2013).

Water hardness is computed by analyzing the concentration of dissolved

metals found in a water body – specifically calcium and magnesium – which can

Introduction

affect the efficiency of societal processes. For example, heavy metal machinery that

work with vast amounts of water perform more economically when the water is soft

(containing very little dissolved metal compounds) because there is less corrosion

and thus, less money is spent in costly maintenance (“Water Hardness and

Alkalinity,” n.d.).

In this report, we will be analyzing three separate experiments in order to

determine the general water quality of Mankato’s tap water system. The results will

allow us to make valid conclusions based upon the chemical makeup of the water,

which will furthermore allow us to better understand the effects that alkalinity,

acidity, and hardness have on our changing world.

Alkalinity. Observations relative to the amount of sulfuric acid needed to put cold

tap water at a pH of 4.5 appeared consistent within our group’s data. After the addition of

the acid to each 25 mL water sample, we noted the amount lost from the burette in order

to calculate the volume required to change the water with the added buffer (bromocresol

green – methyl indicator) into a yellow hue. Our findings can be expressed in Table 1.

Titration trial run 1 2 3

Volume of water sample (mL)

25 25 25

Initial burette reading of acidic

solution (mL)

5.0 3.5 4.3

Final burette reading of EDTA solution

(mL)

5.7 4.3 5.0

Amount of acid added to water (mL)

0.7 0.8 0.7

Ppm of CaCO3 28 32 28

Methods

Results

Table 1. Calculations relative to finding alkalinity of tap water through the addition of an acid.

Please refer to the three attached handouts in regards to the materials and methods used in in the alkalinity, acidity, and hardness labs respectively

According to the results, the average amount of sulfuric acid required to bring the

solution to a yellow hue (which represents the pH change of the water to 4.5) is around

0.7 mL. The alkalinity was calculated as follows:

CaCO3 = [(0.02)(mL of acid)(50,000)] / 25

Where: CaCO3 represents alkalinity in mg/L

0.02 represents the normality of the acid

25 represents the water sample volume in mL

Table 2 refers to relative alkaline levels in mg/L and their effect on a water body.

According to the results from the experiment, our resulting average alkalinity

level fell into the “not sensitive” level, which will be mentioned to a greater extent in the

Discussion.

Table 2. Distribution of the concentration of CaCO3 as dictated by the EPA1.

United States EPA Category Concentration of CaCO3 (in mg/L)

Acidified < 1

Critical < 2

Endangered 2 - 5

Highly Sensitive 5 - 10

Sensitive 10 - 20

Not Sensitive > 20

Acidity. Observations relative to the amount of base required to bring the cold tap

water solution to a pH of 8.3 were as follows in Table 3.

According to the results, the average amount of basic solution needed to put the

water at a pH of 8.3, was 0.2 mL (which turned the solution [with the added

phenothaliene indicator] pink). The acidity was calculated as follows:

CaCO3 = [(0.02)(mL of base)(50,000)] / 25

Where: CaCO3 represents the acidity of the solution in mg/L

0.02 represents the normality of the base

25 represents the water sample volume in mL

Table 3. Calculations relative to finding acidity of tap water through the addition of a base.

Average Acidity = 8Standard Deviation = 4

Titration trial run 1 2 3

Volume of water sample (mL)

25 25 25

Initial burette reading of basic solution (mL)

11.4 11.6 11.7

Final burette reading of basic solution (mL)

11.6 11.7 12

Amount of basic solution added (mL)

0.2 0.1 0.3

Ppm of CaCO38 4 12

Due to the waters calculated higher number (8), we can now determine that that

the solution is more likely to neutralize H+ protons (alkaline), then to neutralize OH- ions

(acid).

Hardness. Observations relative to the amount of ethylenediaminetetraacetate

(EDTA) required to determine the hardness of the water is listed in Table 4.

According to the results, the average amount of EDTA solution needed to determine

water hardness (which turned the solution blue) was 10.5 mL. It was calculated as

follows:

CaCO3 = [(0.02)(mL of EDTA)(50,000)] / 50

Table 4. Calculations relative to finding the hardness of tap water through the addition of an EDTA solution

Average ppm of CaCO3 = 210Standard Deviation = 6.93

Titration trial run 1 2 3

Volume of water sample (mL)

50 50 50

Initial burette reading of EDTA

solution (mL)

0 10.3 20.6

Final burette reading of EDTA

solution (mL)

10.3 20.6 31.5

Amount of EDTA solution added (mL)

10.3 10.3 10.9

Ppm of CaCO3206 206 218

Where: CaCO3 represents water hardness

0.02 represents the normality of the EDTA solution

50 represents the water sample volume in mL

From the equation and additional statistics from the experiment (Table 4), we

have determined the average hardness level to equal 210. Utilizing Table 5, we can define

the metal content as follows:

According to the chart, our average number of 210 falls into the “Hard” water

quality guideline, where there is a greater amount of dissolved ions, such as Na+, K+,

Ca2+, Mg2+, Cl-, and HCO3-, among others, in our tap water supply.

Table 5. Distribution of the amount of dissolved ions in water and their relative hardness concentration classifications

Hardness Level Water Class

0 - 75 Soft

75 - 150 Moderately Hard

150 - 300 Hard

Over 300 Very Hard

The results we received from the alkalinity, acidity, and hardness labs

respectively play an important role in the understanding of the chemical properties of our

local water supply.

To begin, alkalinity represents the capacity of a water body to neutralize H+

protons; in other words, it is a buffer that prevents a lake or stream from becoming too

acidic for life to flourish. From the results of our alkalinity experiment, we have

determined the average water alkalinity level at 29.33 for Mankato’s tap water system.

According to Table 2 from the Results, our local water supply is not sensitive to possible

additions of acid, as alkalinity acts as a buffer.

In a natural environment, alkalinity plays a role in the fertility of a specific water

supply. In aquatic settings, a high alkalinity represents the water’s ability to neutralize

acid rain (additional H+ protons), for example, and maintain the pH of the system at a

relatively neutral 7 – 8 range. In these regards, animal life is able to flourish in an

environment that maintains a relatively constant pH. If a body of water has a low

alkalinity, the pH drops below seven and becomes acidic because there is little to no

buffer to neutralize the acid rain and so life becomes sparse or perishes. In general,

alkalinity represents the capacity of the water to accept H+ protons, while pH represents

the intensity relative to the quantity of H+ suspended in the water body. Most alkalinity

that is found naturally in water bodies comes from calcium carbonate (CaCO3). Alkalinity

is also important in agriculture – for the levels of both the soil and added water must

remain relatively equal.

Discussion

Acidity is the ability of water to neutralize OH- ions. In our lab experiment, we

concluded that the average acidity of the water tested was 8 mg/L. Because of eight’s

location on the pH scale (as shown in Figure 1), we can determine, and furthermore

support from the alkalinity test, that the water is more alkaline than acidic.

This means that our example water supply has a greater ability to neutralize H+ p

We calculated water hardness through finding the average amount of calcium

carbonate (CaCO3) in the sample, which resulted in 210 parts per million (ppm).

According to Table 5 from the Results section, our water sample had received a water

hardness classification of “hard” which represents that a greater amount of dissolved ions

were contained within the examples we used for each trial. In a human society, a water

body which is classified as “soft” has many important benefits. For example, household

detergents are more efficient when utilized with soft water, and factories that operate with

heavy machinery prefer soft water so that their machines run more efficiently and with

less corrosion over their lifetime. Relative to drinking water however, hard water can

actually be beneficial, for it contains many of the minerals we need that are not consumed

from our solid food diets.

Figure 1.

Retrieved from: http://www.abundanthealthcenter.com/blog/the-acid-alkaline-ph-scale

In conclusion, water quality is determined by symbiotic factors that can be

classified in order to make appropriate chemical treatment decisions that will better our

water supply for both human and animal abundance. Water is a very important resource,

and so it is with great importance that it is cared for and utilized in the most efficient way

possible.

1Godfrey, P.J., Mattson M.D. , Walk, M.F. , Kerr P.A. , Zajicek, O.T., and Ruby, A.

(1996). “The Massachusetts Acid Rain Monitoring Project: Ten Years of

Monitoring Massachusetts Lakes and Streams with Volunteers.” University of

Massachusetts Water Resources Research Center. Received from

http://www.uri.edu/ce/wq/ww/Publications/pH&alkalinity.pdf.

2013, February). “The Carbon Dioxide Greenhouse Effect.” The Discovery of Global

Warming. Retrieved from http://www.aip.org/history/climate/co2.htm.

(n.d.). “Water Hardness and Alkalinity.” USGS – Water Quality Information.

Retrieved from http://water.usgs.gov/owq/hardness-alkalinity.html.

Please refer to the attached packets for more information.

References

Appendix