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Tap Water Lab Report

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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 …show more content…

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 …show more content…

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

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