Tap Water Hardness Evaluation in Virginia Tech
Lujia Cheng and Matthew Mills
CHEM 1065, Experiment No.10, November 8, 2016
Abstract. Tap water as a daily water supplement, its quality is critical to residents’ health. In this report, the quality of tap water in Virginia Tech campus was reflected by its hardness. The hardness was measured by the concentration of magnesium and calcium cation. Two methods were used for this evaluation. One is complexometric titration to find out the hardness of the water. The other is AAS to distinguish concentration of magnesium itself.
Introduction. Water is the most important substance. It supports all life forms on earth. And life was believed to originate from water. When it comes to modern era, water
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Tap water (from Hahn Hall North) was sampled. The sampled water was divided into four trails (50.00 mL each). Each was individually titrated with standard solution Na2H2EDTA (0.010 mol/L) with buffer (pH=10) and indicator (calmagite). The solution was dark pink before titration. When the titration reached the end point, the solution turned into blue and the color would not change with more titrant adding. (equation 2) All the data and analysis will be shown in Result and Discussion part below.
Ca^(2+) (aq)+EDTA^(4-) (aq)→〖[CaEDTA]〗^(2-) (aq) (1)
〖[Ca(In)]〗^- (red)+〖H_2 EDTA〗^(2-)→〖[CaEDTA]〗^(2-)+InH^(2-) (blue)+H^+ (2)
Run Atomic Absorption Spectroscopy (AAS) on sample (1:20 dilution) with HNO3 (2 mol/L). AAS calibration standards are mixtures of Mg2+ (from 0.0 to 0.5 ppm increased by 0.1) and HNO3 (2 mol/L) solution.
Results and Discussion.
EDTA complexometric titration. Data and analysis shows below. The calcium of the tap water is around 47.7 ppm. According to USGS, 0 to 60 ppm is classified as soft.3 As it shown, the sample is soft
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The bivariate linear regression relationship between absorbance and concentration of magnesium is, Absorbance = 1.5174 [Mg] - 0.0373 The sample concentration was calculate by this equation, list in Table 3. Error analysis. Since we were unable to analyze AAS. We will only focus on EDTA titration. Although the variance of different trails is really small, they’re still potential error. The end point of EDTA titration is not a suddenly color change but rather the color stop changing. It easy to recognize a rapidly color change. But it's harder to spot the end point of color change. This might cause the actually hardness lower than theoretical.
Conclusions. With two different methods, EDTA titration and AAS analysis, the hardness and manganese concentration was measured. The hardness of Virginia Tech campus is 47.7, soft water. And the manganese concentration is 0.291 ppm.
Acknowledgments. We gratefully acknowledge Dr. Paul A. Deck and our Teacher Assist Ms. Chrissy Duchance
Supporting Information.
References.
1. Sengupta, P., Potential Health Impacts of Hard Water. International journal of preventive medicine 4
We know that that the end point of the titration is reached when, after drop after careful drop of NaOH, the solution in the flask retains its pale pink color while swirling for about 30
In the Chemistry of Natural Waters Lab we were to collect a sample of water, ranging from a fountain, stream, bottle, or tap water. After we collected the samples we all did many tests to see what the hardness was for each one. Water hardness is determined by the amount of Calcium and Magnesium in the water.(2) Water that has more Calcium or Magnesium is considered to be harder than water with less of those two elements. When you use soap and detergent, this is where you see water hardness coming into play in everyday life when you are washing things.
The results for the “Total Hardness” test varied between 20 ppm -128 ppm. The “Total Alkalinity” results varied between 28 ppm – 84 ppm. The results for the “Iron” test were between 0 ppm – 1 ppm. For the “Chloride” the results were as low as 20 ppm and went all the way to 8,000 ppm, but for most part the results were from 20 ppm – 60 ppm. The “Color in Water Low Range” test showed that the max APHA Color was 20 and the lowest APHA Color was 0, which is a great result. Results for the “Turbidity Column” test were Not Applicable (N/A). For both the “Chromate” and “Copper” test the results were 0 ppm. The results for “Zinc” varied between 0 ppm – 2
The Results from ETDA (table 7) show that tap water Mifflin Hall (400 ppm) is hardest than the four other water samples. It is followed by tap water Harleysville (340 ppm), well Water Wyckoff (320 ppm), Stream Water Raleigh (110 ppm) and Tap water Yosemite (80 ppm). This order supports my hypothesis. Tap water Yosemite is relatively soft compared to the other water samples. I have predicted my sample to be the hardness and tap water Yosemite to be the softest. Also, these results support my hypothesis in the assumption that they show that stream water Raleigh is moderately hard as expected. Nevertheless, I expected tap water Yosemite to be relatively soft but the data show that it is moderately hard. In fact, I assumed that tap water Yosemite would be slightly hard because in California ground water is stored in alluvium. They are made up of loose gravel, sands, and silts and they contain a very low concentration of divalent cations. Maybe the fact that rocks vary from the state of California due to the difference in geology might
The solubility of Mg(OH)2 (Ksp = 8.9 10-12) in 1.0 L of a solution buffered (with large capacity) at pH 9.58 is:
Purpose: To determine the percent magnesium by mass in magnesium oxide and to observe if the percentage composition is constant by comparing class results.
Having a hard water with Ca2+ and Mg2+ ions at home could be an annoying thing for many people. When hard water is heated the minerals in it precipitate out including the Ca+ and Mg+2 ions, these mineral start to form a coat on shower doors, bath tops, soap scums which result of addition of soap to hard water and people will find difficulty cleans with soap since hard water lose some affections in dissolving soaps as soaps get mixing with ions and less soap will be dissolving. As a response of this hard water problems water softener came to the market. Water softener works by exchange the hard water ions Ca2+ and Mg2+ with slats such as Na+ and k+ this way the hard water ions will be reduced or eliminated leading to better water quality [2].
The goal of this experiment was to determine the empirical formula for a hydrate of magnesium sulfate and water. The technique that was used was measure the mass of the hydrate and then apply heat to evaporate the water. Then determine the mass of water that was in the hydrate and the mass of the remaining magnesium sulfate. The equation for the hydrate is determined by calculating the mole to mole ratio of the water and the anhydrous. The resulting formula will be formated as: MgSO4*_H2O
Purpose: Finding the concentration of Ca2+ ions in two samples of hard water. Hypothesis: According to the given molarity of CaCl2 in the table, the concentration of sample one should be 0.400 M, making the hardness of the water 400 mg/L and the concentration of sample four should be 0.100 M, making the hardness of the 40.1 mg/L. Procedures: The first experiment was performed to test the procedure of finding Ca2+ ions in a solution. A known amount of CaCl2 and an excess of Na2CO3 were added to a beaker with deionized water in order to make CaCO3 precipitate. The theoretical yield of CaCO3 was calculated from the mass of the CaCl2. The precipitate was filtered from the solution using the Buchner funnel and aspiration filtration.
The mass of the crucible and Mg sample came out to be 24.11g. We found the mass of the Mg to be .25g, after we subtracted the mass of the crucible and mg by the mass of the crucible after the first heating, (24.11g-23.86g). We determined the moles of Mg by dividing the mass of the Mg by 24.3, (.25g/24.3). We found that moles of Mg to be .0102 mol. We found the mass of oxygen by subtracting the mass of the crucible after the final heating by the mass of the crucible and Mg together, (24.25-24.11g). We found the mass of oxygen to be .14g. we determined the moles of oxygen by taking the mass of oxygen and dividing it by 16.00, (.14g/16.00).
Home testing water kits, sourced from Pet Barn will indicate the type of minerals in each batch of water. This information is helpful as it is an easy way to test water quality firsthand. Furthermore, this method is cost effective while still providing an accurate result to base my evidence on.
Additionally, if tap water were used in place of distilled water to dissolve the dried alkali metal carbonate, there would be an increase in the apparent molar mass. Tap water has other ions in it which would have reacted partially with the alkali metal carbonate, making it seems as though there was less alkali metal carbonate than there actually was. Again, this would decrease the moles of alkali metal carbonate and thus increase the molar mass (4). One precaution taken to get the most accurate measurements possible was heating the calcium carbonate for 15 minutes,
The purpose of this experiment is using Compleximetric titration and EDTA to determine the concentration of Mg2+ in solution; and also calculating the percent by mass of MgO in the unknown sample. This procedure results no significant deviations.
Hard water is the water that has a high amount of mineral in it, usually Ca2+ and Mg+. These cations enter the source of water by leaching from minerals within a wet underground layer of water- bearing rock, or an aquifer. According to the WHO, hard water is not harmful to human’s health but it’s a serious problem in the water industry. Household plumbing and appliances are also greatly affected by hard water conditions. Some of the effects include clogged pipes, water heater inefficiency and hard scaling. Hard water is also linked to decreased water flow or water pressure and seized (frozen) valves in faucets,
Table 2: Consists of color extract taken from a red cabbage for a natural indicator. The pH reading that was measured by using the pH meter and the result of the pH reading to determine whether the solution was acidic or basic.