CE 256 Lab 2 Report

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New Mexico State University *

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256L

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Civil Engineering

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Apr 3, 2024

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Electroconductivity Lab #2 CE 256L M02 Lab Date: 09/21/22 Report Due: 09/28/22 Group Members: Louis Mauriot, Cristian Sanchez, Omar Saucedo, Cristina Esquivel, Brittany Hymer

Table of Contents INTRODUCTION ........................................................................................................................................... 3 PROCEDURE ................................................................................................................................................. 3 RESULTS ....................................................................................................................................................... 4 DISCUSSION ................................................................................................................................................. 5 REFERENCES ................................................................................................................................................ 5 APPENDIX .................................................................................................................................................... 5 List of Tables Table 1 Group Results Table 2 Group Results Table 3 Other Groups Results List of Figures Figure 1: Langelier Equation Figure 2: Russel Equation Figure 3: TDS Resultant Equation

INTRODUCTION There is an alternative to last week’s methods of determining the amount of Total Dissolved Solids (TDS, which refers to the total quantity of solids remaining in a solution once filtration and evaporation have been completed) in a solution. This method is a lot more efficient especially on a time scale. Last week, the final lab results were obtained 24 hours after performing the original experiments. Each sample contained within a crucible, or an aluminum dish were stored in a drying oven to estimate the amounts of TSS and TDS for each. This alternate method studied here in this lab allows us to acquire instantaneous results. Using the variation of the number and types of ions present in the solution being tested, we can therefore use electrical conductivity (EC) to help determine the quantity of TDS present in the solution. EC is by definition the ability of a solution to carry an electrical current. Other than the quantity of ions being a varying factor for resultant data, we need to also consider factors such as the temperature of measurement and the mobility valence. It is important to note that bases, salts and solutions of most inorganic acids are on average good conductors. Poor conductors consist of non-dissociative organic compounds. As seen in the previous lab, the amount of TDS contained in a solution sample is highly indicative of the actual potability of water. As mentioned previously, the TDS tests seen last week require a lot of time to perform properly. This EC test we are about to experiment only indicates the TDS level in a sample but is very helpful for many different types of water. In the professional world, the EC test is used quite often. In a laboratory setting, the quality of the DI water used can be measured thanks to the EC test. Out in the field, it also serves a purpose when it comes to measuring changes in surface and groundwater quality caused by a source of groundwater contamination or a wastewater discharge among other causes. The units used for an EC test in a laboratory setting are commonly µmhos/cm (mho = 1/ohm). PROCEDURE This lab consists of a single procedure repeated at different locations around campus. Initially, the lab instructor provides us with a conductivity meter, a bottle of DI water and a plastic drinking cup in the laboratory room. Each laboratory group (which consists of an average of 3-4 people) is then assigned an area on campus. The objective, if we chose to accept it, was to collect at least 3 EC measurements from 3 separate samples in 3 specific locations of the assigned area. In order to fulfill the objective by trying to prevent any kind of human or systematic errors, the usage of the conductivity meter needed to follow very specific steps. At first, the probe part of the conductivity meter or conductivity cell is disinfected. We rinse it with the DI bottle of water. The water sample is then collected from the nearest source of water (which can vary from a water fountain to a pond depending on the location). Once

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disinfected, the cell is then placed in the sample contained within the plastic cup for an approximate duration of 30 seconds. The reading on the conductivity meter screen is then recorded in µmho/cm. This same process is repeated at each individual location. The specific locations assigned to our group were Knox Hall, the Turtle Pond and Skeen Hall. Once all 3 measurements collected at each location, our group reported back to the laboratory room to compare results with other groups assigned to different locations on campus. RESULTS Using the conductivity meter, our group collected the EC data in three separate locations within a certain general area of the New Mexico State campus, which can be found in the table below. Table 1 Group Results Location Resulting EC (in µmho/cm) Resulting TDS (in mg/L) Knox Hall 720 460.8 Turtle Pond 1082 692.5 Skeen Hall 713 456.3

Map of the New Mexico State Campus with corresponding EC data Figure 1: Langelier Equation µ= 2.5*10^-5 * TDS where µ: µmho/cm and TDS: mg/L Figure 2: Russel Equation µ= 1.6*10^-5 *EC where µ and EC: µmho/cm Figure 3: TDS Resultant Equation TDS = ( 1.6*10^-5 *EC) / (2.5*10^-5) Milton Hall µmho/cm Hernandez Hall 641 µmho/cm Corbett 740 µmho/cm Turtle Pond 1082 µmho/cm Skeen Hall 713 µmho/cm Knox Hall 720 µmho/cm Chemistry Building 660 µmho/cm Goddard Hall 633 µmho/cm Jett Hall 676 µmho/cm Hadley Hall 680 µmho/cm Domenici Hall 710 µmho/cm Foster Hall 678 µmho/cm

DISCUSSION The apparatus used for this particular lab is a conductivity meter. The process to use it is simple but does require a few steps. Firstly, the probe part of the conductivity meter or conductivity cell is disinfected. We rinse it with a DI bottle of water. Once disinfected, the conductivity cell is then placed in the sample for an approximate duration of 30 seconds. The reading on the conductivity meter screen is then read and recorded in µmho/cm. According to the Department of Civil Engineering here at NMSU (2022), the typical freshwater values for EC distilled water are 0.5 to 2 µmhos/cm and after two weeks of exposure can increase up to between 2 and 4 µmhos/cm due to exterior factors such as ammonia and atmospheric carbon dioxide. In the real world, the EC test is used quite often. According to the Department of Civil Engineering here at NMSU (2022), in a laboratory setting, the quality of the DI water used can be measured thanks to the EC test. Out in the field, it also serves a purpose when it comes to measuring changes in surface and groundwater quality caused by a source of groundwater contamination or a wastewater discharge among other causes. The two measurements obtained for Skeen Hall and Knox Hall are very close (only a difference of 7 µmho/cm) between each. When comparing the measurement obtained from the turtle pond water sample to those latter however, there is a drastic difference (Almost a 400 µmho/cm difference between the turtle pond measurement and the other two locations). Nevertheless, this does make sense as we can visually inspect each water sample. It is easily noticeable that the sample collected from the turtle pond is very murky. There are a lot of particles floating around in the sample. This contrast with the samples from Knox Hall and Skeen Hall which came from water fountains. This visual difference aligns with the measurement difference. The turtle pond is the only water non drinkable source where the EC measurement was collected. All measurements from other locations are also from drinkable sources which explains why they all are similar (refer to table 3) and range between 600 and 700 µmho/cm. REFERENCES - Department of Civil Engineering. (2022, Fall). CE 256 lab manual. Las Cruces, New Mexico: New Mexico State University. Retrieved from class website: Normality and Standardization.pdf: 2022 Fall - C E-256 L-M02-ENVMTL. SCIENCE LAB (instructure.com)

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APPENDIX Table 2 Group Results Location Resulting EC (in µmho/cm) Resulting TDS (in mg/L) Knox Hall 720 460.8 Turtle Pond 1082 692.5 Skeen Hall 713 456.3 Table 3 Other Groups Results Location Resulting EC (in µmho/cm) Resulting TDS (in mg/L) Hernandez Hall 641 410.2 Jett Hall 676 432.6 Goddard Hall 633 405 Chemistry Building 660 422.4 Foster Hall 678 433.9 Hadley Hall 680 435.2 Domenici Hall 710 454.4 Milton Hall 697 446.1 Corbett 740 437.6 Figure 4: Sample Calculation of TDS TDS = (1.6*10^-5 * 740) / (2.5*10^-5) = 473.6 mg/L

CE 256 Lab 2 Report

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