write 5

Department of Civil Engineering

University of North Dakota

243 Centennial Drive Stop 8115

Grand Forks, ND 58202

Bruce Dockter

Upson II

243 Centennial Drive Stop 8115

Grand Forks, ND 58202

Subject: Laboratory Report 7 Alkalinity and Hardness

Dear Mr. Dockter,

This is Laboratory Report 7 for CE 431L Environmental Engineering Laboratory in the 2023 summer semester. I submit this report to you for your consideration. The objectives of this lab were to measure the alkalinity of raw water and coagulated water in the previous lab as well as the alkalinity of a tap water sample and a boiled tap water sample. The techniques used in this lab included measuring the alkalinity and hardness of three water samples, which include Red River water, tap water, and distilled water.

This report was done by members Mustafa Dahir, Dustin Gilchrist, Devon Telligman, and Abdiweli Yusuf. Any questions related to the technical or administrative aspects of this report should be directed to my email at [email protected]. Thank you for your time and consideration of this report.

Sincerely,

Devon Telligman

Enclosure: Laboratory Report 7 Alkalinity and Hardness

Laboratory Report 7

Alkalinity and Hardness

Prepared by:

Mustafa Dahir

Dustin Gilchrist

Devon Telligman

Abdiweli Yusuf

Prepared for:

Bruce Dockter

University of North Dakota Civil Engineering Department

CE 431L Environmental Engineering Laboratory

Summer 2023

Lab Completed: 5/25/2023

Date Submitted: 6/30/2023

Table of Contents

1. OBJECTIVE ....................................................................................................................4

2. THEORY …......................................................................................................................4

3. EXPERIMENTAL DESIGN …......................................................................................4

4. RELATIVE EQUATIONS ….........................................................................................5

5. EQUIPMENT AND MATERIALS …...........................................................................5

6. PROCEDURE …..............................................................................................................7

7. RESULTS ….....................................................................................................................9

8. DISCUSSION AND CONCLUSIONS ….....................................................................13

9. REFERENCES …...........................................................................................................15

10. APPENDICES …............................................................................................................15

List of Tables

Table 1 Equipment and Materials Used for Determining Alkalinity....................................................5

Table 2 Equipment and Materials Used for Determining Calcium Hardness......................................6

Table 3 Equipment and Materials Used for Determining Total Hardness...........................................6

Table 4 Data Obtained for Determining Alkalinity................................................................................9

Table 5 Calculated Data for Determining Alkalinity..............................................................................9

Table 6 Data Obtained for Determining Hardness...............................................................................10

Table 7 Calculated Values for Calcium, Total and Magnesium Hardness..........................................10

Table 8 Meq, Carbonate and Non-Carbonate Hardness Values for Tap Water................................10

Table 9 Meq, Carbonate and Non-Carbonate Hardness Values for Red River Water......................11

List of Figures

Figure 1 Meq/L Bar Graph for Carbonate and Non-Carbonate Hardness of Tap Water.................12

Figure 2 Meq/L Bar Graph for Carbonate and Non-Carbonate Hardness for River Water............13

1. OBJECTIVE

The goal of this lab is to assess the alkalinity of both untreated tap water from Grand Forks

Drinking-water Treatment Plant and raw Red River water. Alkalinity is crucial because it gives

water the ability to act as a buffer, preventing pH changes when an acid or base is introduced.

The lab's other objective is to gauge the degree of hardness in samples of distilled, tap, and Red

River water. The HACH's methodology will be used to calculate the calcium content and overall

hardness. The magnesium hardness will be different from both the overall hardness and the

calcium hardness.

2. THEORY

A buffer solution is a substance that withstands significant pH fluctuations caused by the

addition of an acid or base or by diluting the substance. A buffer is a solution made up of a weak

acid and its salt. Alkalinity is the term used to describe the water's ability to take in protons H+

ions. Natural waters become hard due to the breakdown of calcium and magnesium-containing

minerals found in geologic formations.

3. EXPERIMENTAL DESIGN

Alkalinity is the degree of the capacity of water to neutralize acids from precipitation or

wastewater. Alkalinity secures sea-going life by buffering out fast pH changes that can be

destructive to angle and other sea-going life. Alkalinity is critical since it impacts cleaning forms

such as anaerobic assimilation. The free variable in this lab is the beginning alkalinity level

within the tap and red stream water. The subordinate factors in this lab would be the marker

powders utilized. The hardness experiment consists of testing tap water, water from the red river,

and refined water for calcium hardness and adding up to hardness in arrange to decide the sum of

lime required to soften the water. The independent factors were the sums of hardness within the

test water. The subordinate factors were the sums of lime required to soften the water.

4. RELEVANT EQUATIONS

To calculate the concentration:

Digits used × digit multiplier = mg/L as CaCO3

CO_2(aq) +H_2 O ↔ H_2 CO_3 (10.1.1)

H_2 CO_3 ↔ H^+ + HCO_3^- (10.1.2)

H_2 CO_3^- ↔ H^+ + CO_3^(2-) (10.1.3)

CaCO_3(s) ↔ Ca^(2+)+CO_3^(2-) (10.1.4)

Mg(HCO_3 )_2+2Ca(OH)_2 → 2CaCO_3↓ + Mg(OH)_2↓ (10.1.5)

5. EQUIPMENT AND MATERIALS

Table 1 shows the equipment as well as the materials used during the alkalinity portion of the

lab.

Table 1 Equipment and Materials Used for Determining Alkalinity

Equipment pH Meter and Probe

Digital Titrator Delivery Tube for Digital Titrator Sulfuric Acid Titration Cartridge

Materials Bromescol Green-Methyl Red Indicator

Phenolphthalein Indicator Powder Pillow Graduated Cylinder

Erlenmeyer flask, 250-mL Deionized Water

Table 2 shows the equipment as well as the materials used during the calcium hardness portion

of the lab.

Table 2 Equipment and Materials Used for Determining Calcium Hardness

Equipment EDTA Titration Cartridge

Digital Titrator Delivery Tube for Digital Titrator

Materials CalVer 2 Calcium Indicator Powder Pillow

Potassium Hydroxide Standard Solution, 8 N Graduated Cylinder

Erlenmeyer Flask, 250-mL Deionized Water

Table 3 shows the equipment as well as the materials used during the total hardness portion of

the lab.

Table 3 Equipment and Materials Used for Determining Total Hardness

Equipment EDTA Titration Cartridge

Digital Titrator Delivery Tube for Digital Titrator

Materials ManVer 2 Hardness Indicator Powder Pillow

Hardness 1 Buffer Solution Graduated Cylinder

Erlenmeyer Flask, 250-mL Deionized Water

6. PROCEDURE

The first step of the alkalinity portion of the lab is to select a sample volume and titration

cartridge from Table 1 on page 3 of the Hach Alkalinity Procedure. The second step is to insert a

clean delivery tube into the digital titration cartridge and attach the cartridge to the digital

titrator. The third step is to hold the digital titrator with the cartridge tip up, turn the delivery

knob to eject air and a few drops of the titrant, reset the counter to zero, and clean the tip. The

fourth step is to use a graduated cylinder to measure the sample volume selected. The fifth step is

to pour the sample into a clean, 250-milliliter Erlenmeyer flask. The sixth step is to dilute the

sample with deionized water until the sample volume is approximately 100 milliliters. This step

is to be done if the sample volume is less than 100 milliliters. The seventh step is to add the

contents of one phenolphthalein indicator powder pillow. The eighth step is to mix the solution

by swirling the flask. The ninth step is to put the end of the delivery tube completely into the

solution, swirl the flask, turn the knob on the digital titrator to add titrant to the solution, continue

to swirl the flask, add titrant until the color changes from pink to colorless, and record the

number of digits on the counter. The tenth step is to add the contents of one bromescol green-

methyl red indicator powder pillow. The eleventh step is to mix the solution by swirling the

flask. The twelfth step is to put the end of the delivery tube completely into the solution, swirl

the flask, turn the knob on the digital titrator to add titrant to the solution, continue to swirl the

flask, add titrant until the color changes to light pink, and record the number of digits on the

counter.

The first step in the calcium hardness portion of the lab is to select a sample volume and titration

cartridge from Table 1 on page 3 of the Hach Hardness Method 8204. The second step is to

insert a clean delivery tube into the digital titration cartridge and attach the cartridge to the digital

titrator. The third step is to hold the digital titrator with the cartridge tip up, turn the delivery

knob to eject air and a few drops of the titrant, reset the counter to zero, and clean the tip. The

fourth step is to use a graduated cylinder to measure the sample volume selected. The fifth step is

to pour the sample into a clean, 250-milliliter Erlenmeyer flask. The sixth step is to add 2

milliliters of 8 N potassium hydroxide standard solution if the sample volume is 100 milliliters

and add 1 milliliter of 8 N potassium hydroxide standard solution if the sample volume is 50

milliliters or less. The seventh step is to mix the solution by swirling the flask. The eighth step is

to dilute the solution with deionized water until the sample volume is around 100 milliliters. This

step is to be done if the sample volume is less than 100 milliliters. The ninth step is to add the

contents of one CalVer 2 Calcium Indicator Powder Pillow. The tenth step is to mix the solution

by swirling the flask. The eleventh step is to put the end of the delivery tube completely into the

solution, swirl the flask, turn the knob on the digital titrator to add titrant to the solution, continue

to swirl the flask, add titrant until the color changes from red to pure blue, and record the number

of digits on the counter.

The first step in the total hardness portion of the lab is to select a sample volume and titration

cartridge from Table 1 on page 3 of the Hach Hardness Method 8213. The second step is to

insert a clean delivery tube into the digital titration cartridge and attach the cartridge to the digital

titration cartridge. The third step is to hold the digital titrator with the cartridge tip up, turn the

delivery knob to eject air and a few drops of the titrant, reset the counter to zero, and clean the

tip. The fourth step is to use a graduated cylinder to measure the sample volume selected. The

fifth step is to pour the sample into a clean, 250-milliliter Erlenmeyer flask. The sixth step is to

dilute the solution with deionized water until the sample volume is around 100 milliliters. This

step is to be done if the sample volume is less than 100 milliliters. The seventh step is to add 2

milliliters of the hardness 1 buffer solution. The eighth step is to mix the solution by swirling the

flask. The ninth step is to add the contents of one ManVer 2 hardness indicator powder pillow.

The tenth step is to mix the solution by swirling the flask. The eleventh step is to put the end of

the delivery tube completely into the solution, swirl the flask, turn the knob on the digital titrator

to add titrant to the solution, continue to swirl the flask, add titrant until the color changes from

red to pure blue, and record the number of digits on the counter.

7. RESULTS

Table 4 Data Obtained for Determining Alkalinity

DI Water (ml) Tap Water (ml) River Water P-Alkalinity T-Alkalinity Multiplier

100 0 0 0 0 1

0 100 0 0 74 1

80 0 20 0 19 5

As expected, the measured and adjusted phenolphthalein (P) alkalinity, measured and

adjusted total (T) alkalinity, hydroxide alkalinity, carbonate alkalinity, and bicarbonate alkalinity

were all determined to be zero mg/L (as CaCO3) for the deionized water sample. Similarly, the

P-alkalinity, hydroxide alkalinity, and carbonate alkalinity were also found to be zero for all

samples. Because the only type of alkalinity present in the two samples containing river water

was found to be bicarbonate, it makes sense that the total alkalinity and bicarbonate alkalinities

would be the same value, since the total—by definition—must equal the sum of the individual

alkalinities.

Table 5 Calculated Data for Determining Alkalinity

All Alkalinity Values Reported as mg/L (as CaCO3)

P-Alkalinity Adjusted

T-Alkalinity Adjusted

Hydroxide Alkalinity Carbonate Alkalinity Bicarbonate

Alkalinity

DI 0 0 0 0 0

Tap 0 74 0 0 74

Red River 0 95 0 0 95

Table 6 Data Obtained for Determining Hardness

DI Water (ml) Tap Water (ml) River Water Calcium

Hardness Total

Hardness Multiplier

100 0 0 28 19 0.1

75 25 0 234 409 0.4

0 0 100 80 132 1

Table 7 Calculated Values for Calcium, Total and Magnesium Hardness

As CaCO3

Cal Adjusted Total Adjusted Magnesium Hardness

2.8 1.9 -0.9

93.6 163.6 70

80 132 52

The total hardness for the tap water was determined to be 163.6 mg/L which was

distributed as 93.6 mg/L of calcium hardness and 70 mg/L magnesium hardness. The river water

was determined to have a calcium hardness of 80 mg/L and a magnesium hardness of 52 mg/L,

for a combined total hardness of 132 mg/L.

Table 8 Meq, Carbonate and Non-Carbonate Hardness Values for Tap Water

Tap Water Meq/L

mg/L (CaCO3) mg/Meq Meq/l Carbonate Harness

Non-Carbonate Hardness

Calcium 93.6 50 1.872 1.48 0.392

Magnesium 70 50 1.4 0 1.4

Bicarbonate 74 50 1.48

Figure 1 Meq/L Bar Graph for Carbonate and Non-Carbonate Hardness of Tap Water

Table 8 and Figure 1 show the carbonate and non-carbonate hardness values and distributions for the tap water sample. Because none of the hardness was present as magnesium carbonate hardness, the amount of lime needed to soften it is equal to the total amount of carbonate hardness present. The lime dosage needed to soften the tap water is therefore 1.48 Meq/L, or 74 mg/L of lime as CaCO3. The soda ash required would then be equal to the remaining non-carbonate hardness of 0.792 Meq/L or 41.976 Na2CO3.

Table 9 Meq, Carbonate and Non-Carbonate Hardness Values for Red River Water

Red River Meq/L

mg/L (CaCO3) mg/Meq Meq/l Carbonate Harness

Non-Carbonate Hardness

Calcium 80 50 1.6 1.6 0

Magnesi um 52 50 1.04 0.3 0.74

Bicarbo nate 95 50 1.9

Figure 2 Meq/L Bar Graph for Carbonate and Non-Carbonate Hardness for River Water

Table 9 and Figure 2 show the carbonate and non-carbonate hardness values and distributions

for the Red River sample. Because some of the hardness exists as magnesium carbonate

hardness, the lime dosage is slightly higher than the hardness value. Hardness in the form of Mg

(HCO3)2 requires double the amount of lime for softening. This makes the total lime dosage

equal to the total carbonate hardness plus an additional dose equal to the Mg(HCO3)2 hardness of

0.3 Meq/l. The total lime dosage is therefore 2.2 Meq/L or 110 mg/L lime as CaCO3. The soda

ash required would be equal to the total non-carbonate hardness of 0.74 Meq/L, or 39.22 mg/L of

Na2CO3.

8. DISCUSSION AND CONCLUSIONS

As previously mentioned, and as seen in Table 5, bicarbonate alkalinity is the

predominant type of alkalinity present in our water samples. This is consistent with patterns

described in the required literature for this course lecture in regard to surface water in general.

Interestingly, the reason that alkalinity is most likely to exist naturally as HCO3 in surface water

is best understood from a chemical and geological standpoint, rather than a hydrological one.

Carbon dioxide is absorbed by water when air contacts its surface or when biological processes

within the water source release it naturally. Once present, this aqueous carbon dioxide reacts

chemically with the water molecules (H2O) to produce carbonic acid (H2CO3) which quickly

ionizes into a bicarbonate anion (HCO3 -) by releasing a Hydrogen cation (H+) in order to become

more stable. This process of releasing positively charged ions actually causes the pH to drop,

increasing the acidity of the water. This reaction is the main cause of ocean acidification.

Under far less acidic conditions, bicarbonate molecules will ionize a second time

producing a carbonate anion (CO3 2-) and yet another hydrogen cation (H+); however, high levels

of CO2 present in water, will force carbonate ions to bond with excess hydrogen in favor of

producing bicarbonate in order to stabilize the pH. This means that the natural levels of Luckily,

most surface water—including oceans—will come into physical contact with minerals that

contain natural buffers like calcium carbonate (CaCO3), such as limestone or the shells and bones

of the creatures that inhabit the water. When this strong base is exposed to a high level of acidity,

it is dissolved to produce disassociated CO3 2- ions to replace the ones consumed by the CO2. This

means that in order to balance the ocean's pH, many important mineral bound organisms (such as

corals) are destroyed in the process.

The hardness values for the two water sources don’t line up with what one would expect.

Because both values are considered hard water, it would make sense that the river water would

be softened to a lower hardness value before being sent through the distribution system;

however, it appears that the water leaves the treatment facility harder than it was when it entered.

In conclusion, the phenolphthalein alkalinity, hydroxide alkalinity, and carbonate alkalinity

were determined to be zero mg/L (as CaCO3) for all samples. The total and bicarbonate alkalinity

for the tap water were both found to be 74 mg/L. The total and bicarbonate alkalinity for the Red

River water were again the same and determined to be 95 mg/L. The calcium hardness for pure

Red River water was found to be 80 mg/L, while its total hardness was 132 mg/L. The calcium

and total hardness for the diluted tap water were determined to be 93.6 mg/L and 163.6 mg/L,

respectively. This yielded a magnesium hardness of 70 mg/L for the tap water and 52 mg/L for

the river water. Because the total hardness values for the tap and river water were above 120

mg/L as CaCO3, both sources were determined to be hard water. The amount of lime (as CaCO3)

required to treat each water source was calculated to be 74 mg/L for the tap water and 110 mg/L

for the river water. The soda ash dosages required to treat the tap and red river water were

determined to be 41.976 mg/L and 39.22 mg/L of Na2CO3, respectively.

9. REFERENCES

1. Viessman, W., Hammer, M. J., Perez, E. M., & Chadik, P. A. (2015). Water

Supply and pollution control (8th ed.). Pearson lndia Education.

10. APPENDICES

10.1 Equations

Alkalinity

CO2 (aq )+H 2O↔H 2CO3 (10.1.1)

H 2C O3↔H+¿+HCO3 −¿¿¿ (10.1.2)

H 2C O3 −¿↔H+¿+C O3

2−¿¿¿¿ (10.1.3)

CaCO3 (s )↔Ca 2+¿+CO3

2−¿¿¿ (10.1.4)

Hardness

Mg (HCO3 )2+2Ca (OH )2→2CaCO3↓+Mg (OH )2↓ (10.1.5)