hard water

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Feb 20, 2024

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Determination of total water hardness Chiara Palacios, Gianni Johnson , Maya Golic , Jazmin Perez 11/02/2023 Thursday/ 1:30 pm

Introduction Water hardness is defined as the amount of dissolved mineralized ions in water. Water that flows through lakes, rivers, streams, and aquifers percolates through the rocks. Water becomes enriched largely with cations of magnesium and calcium as well as anions of carbonates, phosphates, sulfates, chlorides, etc. Human activity as well as natural mineralization affects the amount of dissolved ions. High amounts of cations, Mg and Ca, increases water hardness due to the contribution of sparingly soluble carbonates(especially CaCO 3), phosphates and sulfates characterized by low solubility products. The way that it affects the quality of water is not through the dissolved anions or cations, but the insoluble salts they form. There are no health risks associated with drinking hard water but there are disadvantages in the way that it can cost money to use hard water: it increases hot water bills, the build up of mineral scale damages the plumbing system, an increase in time and fuel for cooking, and the increase of the use of cleaners such as detergents, shampoos, and soaps. Water softening has been used to minimize the adverse effects of water hardness in homes and in the industry. The process uses a cation exchange resin to remove cations on calcium and magnesium from the water. Deionized water is an example of water treated using ion catching columns. The purpose of this experiment was to determine the content of M gz+ and Ca’" in tap water by using back titration and the use of metal ion’s chelator EDTA. The molecule of EDTA has a structure that allows it to grab M g2+ and Ca”" ionsina 1 to 1 ratio. With this information we compared the hardness of the lab room’s tap water as well as the deionized water that we use daily in the lab as well. We then would become familiar with expressing the contents of M g2+

and Ca’tin ppm. With the data we obtained we then compared it with data from published water quality reports. Materials e Tap Water e DI Water e (.025 M standardized solution of Mg(NO 3)2 e 0.025 M Ethylenediamine tetra-acetic acid, (EDTA) ® 1% Eriochrome black T solution e Burette e Burette clamps e Burette stands e 50 mL Graduated Cylinder o 250 mL erlenmeyer flask Procedure For this experiment, two types of water will be used. Half of the group will use DI water, while the other half will use tap water. The first half will use DI water. To begin the experiment, set up your burette, stand, and clamps. Once everything has been set up, fill the burette with MgNO . Fill the burette up to 10 mL. Next you are going to prepare your solution in a 250 mL erlenmeyer flask. Use a graduated cylinder to measure 50 mL of DI water. Pour it into the 250 mL erlenmeyer flask. Then, you are going to add 10 mL of 0.025 M Ethylenediamine tetra-acetic acid, (EDTA). Then are going to

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add 5.0 mL of NH 3N H 4C [ buffer, pH 10. Finally, you are going to add three drops of 1% Eriochrome black T solution. Make sure that you add these last two chemicals under a fume hood. This is so you will not leave a strong and unpleasant smell in the lab area. After mixing everything in your erlenmeyer flask, the whole solution should be blue. Next, you are going to titrate the MgNO 3 from the burette, and swirl the erlenmeyer flask as you add it. keep adding until the solution turns red. This should signify the titration. Repeat the process two more times. The other half will use tap water instead of DI water, but the steps are the same. First, set up your burette, stand, and clamps. Then, fill the burette with 10 mL of MgNO . Next, prepare a solution in a 250 mL erlenmeyer flask. measure 50 mL of tap water using a graduated cylinder. Pour it into the 250 mL erlenmeyer flask. Then, you are going to add 10 mL of 0.025 M Ethylenediamine tetra-acetic acid, (EDTA), 5.0 mL of NH 3N H 4C [ buffer, pH 10, and add three drops of 1% Eriochrome black T solution. Make sure that you add these last two chemicals under a fume hood. You do not want to leave a strong and unpleasant smell in the lab area(!!!).The whole solution should be blue after mixing everything. Next, you are going to add MgNO ; from the burette, and swirl the erlenmeyer flask as you add it. keep adding until the solution turns red. Repeat the process two more times. Experimental Data and Calculations = t=~] - 1]

1] 50 100002 0009 347510 2.5 x10° 5 x 10 5 2 50 0.0002 0.00998 |5 495 x107* 5 x 107 1 %x10° 5 3 50 0.0002 0.00980 2 45 x 10 5 % 10°° 1 % 10~* S Average: 553 x 10" Table 3. Comparison of hardness of deionized and tap water. Type of | Moles of total Total molar Hardness of water in Hardness in water Mg?* and Ca®>* | concentration of g/L of CaCO; ppm of CaCO, Mg*" and Ca** (mol/L) Mesa 1.45 % 10" 29 % 10> 0.29 290.25 Tap water Sample 1 DIwater | 5 5 « 197° 5 %10 > 0.005 5 Sample 1 Calculations 1) total moles of EDTA

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0.025moles omoles % 0.01 = 2.5 x 10 moles 2) moles of excess EDTA Molarity of EDTA = 0.025M Volume = 0.00420 0.025M X 0.00420L = 1.05 X 10 ‘moles 3) moles of EDTA bound to Mg®* and Ca®" in a sample of tap water Total moles of EDTA = 2.5 X 10 ‘moles Moles of excess = 1.05 X 10 ‘moles —4 —4 2.5 Xx10 moles — 1.05 X 10 moles —4 = 1.45 X 10 moles 4) Total hardness of water in ppm (mg/L) of CaCO; Total molar concentration = 0.0029M ) __100.0869g Molar concentration of CaCO; = Tmol CaCO3 0.0029moles 100.0869g 9 1L X TmolCac03 — 0.297 0.00124-4L x 5514 = 290,254 g L = 29 ppm Discussion/Questions

1) Compare your total hardness of water with that reported in the water quality reports: a. Mesa, AZ Water hardness in Mesa fluctuates between 12 and 22 ppm, depending on the water source. The white, chalky coating on a home's faucet or shower doors is one indicator of hard water. Comparing this to what we concluded to be the hardness of water, our results were fairly high and within a decent amount of range to the Mesa’s water hardness. https://www.mesaaz.gov/residents/water-resources/services/water-quality b. Tempe, AZ Water hardness in Tempe flatlines to about 12 ppm depending on the many sources for a water source. Contaminants are found most commonly in the Tempe location for water sources and some of those include TTHM’s, Radiological, Chromium, and Arsenic. Our range for the water hardness to be considered soft was anywhere from 0 to 60. This city falls underneath that category. Comparing it to our range for water hardness, it is extremely high. https://www.tempe.gov/government/public-works/water/water-quality/annual-wat er-reports c. Phoenix, AZ Water hardness in Phoenix is fairly high at about 230 ppm (parts per million) when compared to our quantity of water hardness range that classifies this type of water hardness as “very hard.” Any type of ppm that is higher or above 180 ppm is considered to be very high and result in a very hard water hardness. Considering that Phoenix is double the ranged amount, that is extreme. When

looking at the ppm you also want to look at the gpg which are the grains per gallon to classify both to see if either one falls on the scale range. Our tap water for water hardness scaled in about 290 ppm which is just the same as phoenix’s water hardness. https://www.phoenix.gov/waterservicessite/Pages/qualtreports.aspx 2) List 2-3 sources of error in this experiment and describe how to correct them. Some sources of error in this experiment could occur from the amount of MgNO?2 titrated into the flask of the rest of the solutions combined. The titration trials will end once when the solution has turned a visibly dark color of pink. The calculation after recording the volume amount that was used for that given trial, was calculated. Another error that could have occurred is improper pouring of the edta, 3 drops of the indicator, buffer solution and the given tap or deionized water. 3) Classify the hardness in the sample that you tested according to the following table used in water quality reports. Based on your experience, how does hardness of water affect the quality of drinking water? Tap water: 0.029 g/L. CaCO 2 DI water: 0.005 g/L CaC 03 Hardness in first sample, tap water, 290.25 ppm (Very Hard) Hardness in the second sample, DI water, 5 ppm (Soft)

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Using the table and analyzing the data for the units of ppm, we have concluded that the first sample that was tested, tap water, holds the parts per million with over 180 making the total water hardness classified as very hard. The second sample, not so much coming in with only 5 parts per million which is not close enough to that moderately hard range. Water Hardness Classification - TR Milligrams per Liter Classification (mg/L) or Parts per Gallon (gpg) i Million (ppm) Soft 0-3.5 0-60 Moderately Hard 3.6-7.0 61-120 Hard 7.1-10.5 121-180 Very Hard Over 10.5 Over 180 4) Compare the hardness in samples of tap water and DI water. Were you able to measure any amount of total Ca®" and Mg*" in DI water? Why the DI water is called deionized? How was it treated? The hardness in samples of tap water and DI water when compared to each other, the tap water has more of a higher dense water hardness compared to DI water. We were able to calculate and find the amount of moles of Ca’and M gz+ in DI water which happened to —6 : .. : : be 2.5 X 10 . DI or Demineralization means the removal of ions. Ions are electrically charged atoms or molecules present in water with a net positive or negative charge. These ions are regarded as contaminants in many applications that utilize water as a rinse or ingredient and must be eliminated from the water. 5) Explain the unit of ppm for a hardness of water 10

The unit of ppm is recognized by the parts per million of water hardness, every one million units of the water is a hardness mineral. Ultimately, ppm is the measurement of how much magnesium and calcium are determined to classify water hardness. Appendix - Original data OSESKIFVBIALZS & 3\.3 VW(/ 1.9% AL ST OISl 0.1l O Tt | T ‘ﬂfll 4,20 mL HZ\, W0 ml #2] 5104l o) “ 11