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Chemistry

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Dec 6, 2023

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Acid Neutralizing Capacity Lab Elizabeth German Lab Partners: Tehya Fulcher, Otto Martinez, & Brandon Sheetz Lab preformed: 02/13/2023 1 | P a g e

I. Abstract During, this experiment the acid neutralization capacity of six different collected water samples was tested. These samples ranged from deionized water to water containing inorganic and organic materials from various bodies of water. These samples were titrated using 0.001 N HCl, with the intention of simulating acid rain. Waters with higher acid neutralization capacities took more HCl to change the pH. The color indicator took longer to occur due to the larger amounts of bicarbonate and carbonate ions present in waters of high acid neutralization capacity. In this lab, the marine saltwater and boat basin samples that had the highest amounts of bicarbonate and carbonate ions took the most HCl to titrate them. While the sample that needed the lowest amount of HCl was found in the standard sample, which had the lowest amount of bicarbonate and carbonate ions. II. Introduction The acidity of a solution can be measured using the pH scale, and aquatic organisms adapt to a water’s narrow range of pH values. The formal definition of pH is + ¿ H ¿ pH =− log ¿ . The pH of pure water is 7, which is neutral, because the water molecules can dissociate to form equal concentrations of a hydrogen cation, H+, and a hydroxide anion, OH- or A-. When the hydrogen ion concentration is increased, the pH drops making it an acidic solution, and if it is decreased, the pH rises to make it a basic solution. Changes in acidity or alkalinity of natural bodies of water can impact the aquatic community, and human activity is rapidly increasing this factor. Bicarbonate and carbonate anions are considered the most important acid-neutralizing 2 | P a g e

substances. A chemical reaction occurs when entering water that allows these chemicals to produce or remove hydrogen ions to maintain a relatively stable pH. These anions are usually added through the weathering of sedimentary rocks, or atmospheric carbon dioxide dissolving into water. The increase in carbon dioxide in the atmosphere however has resulted in a process known as "ocean acidification." Additionally, the products of combustion from fossil fuels can combine with water droplets to form acid rain and result in a lowering of the pH. The acid neutralizing capacity (ANC), which particularly refers to seawater, is the amount of acid that can be neutralized in water. The ANC of fresh water is more often exposed to areas of weak acid anion sources like soils, rocks, and vegetation, that can neutralize the acid. Freshwater may also have runoff occur quickly before a reaction can happen. However, seawater has a relatively large ANC due to dissolved bicarbonate anions. Before conducting this experiment, it was hypothesized that seawater samples would have a higher ANC compared to freshwater samples, and the highest ANC will be obtained from the saltwater beach sample because it is seawater that is in a less trafficked area, which infers fewer pollutants. III. Materials and Methods In this laboratory experiment, various materials were used: a burette with a stand, three 100 mL beakers, marine saltwater, samples of boat basin water, pond water, standard deionized water, canal water, groundwater, a standard solution of 0.001 M sodium bicarbonate water, a 50 ml pipet with pipette bulb, 0.01 N HCl solution, methyl orange indicator, magnetic stir bar and a stir plate were used. First, the burette was filled up with the 0.01 N HCl acid solution and place securely on the stand above the stir plate and the exact amount of HCl added to the 3 | P a g e

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burette was recorded. Next exactly 50 mL of the standard solution was measured out with a pipette and placed into a beaker. Two drops of the methyl orange indicator were then added along with the stir bar. The beaker was then placed upon the stir plate under the burette of HCl and the stir plate was turned on low. The solution was then titrated until a pinkish-orange color was achieved. The volume difference of HCl was recorded and the amount used to titrate the solution was calculated. The first beaker was set aside while these steps were repeated two more times for this solution and the next two trials were color compared to the first. These steps were repeated for each sample, rinsing all equipment with deionized water in between each different sample. When samples were done being used, they were properly disposed of into their assigned waste containers. IV. Results The results from the titration procedure were used to calculate the ANC for each sample along with the mean and standard deviation for acid volume added for the 0.001 M sodium. Standard Deionized Water (Sample 1), Boat Basin (Sample 2), Pond Water (Sample 3), Canal Water (Sample 4), Marine Salt Water (Sample 5), and Ground Water (Sample 6) means and standard deviations were accordingly 6 ±0.36 mL (Sample 1), 15.17 ± 1.36 mL (Sample 2), 10.47 ± 5.34 mL (Sample 3), 1.1 ± 0.1 mL (Sample 4), 11.93 ± 0.60 mL (Sample 5), 7.33 ± 0.70 mL (Sample 6). The 95% confidence interval (CI), in ascending order, was 6 ± 0.41 mL, 15.17 ±1.54 mL, 10.47 ± 6.04 mL, 1.1 ± 0.11 mL, 11.93 ± 0.68 mL, and 7.33 ± 0.80 mL . The calculated ANC of each sample was 0.0012 eq/liter, 0.0030 eq/liter, 0.0021 eq/liter, 0.0022 eq/liter, 0.0024 eq/liter, and 0.0015 eq/liter. V. Discussion 4 | P a g e

The results of the experiment show the highest mean for acid added until the endpoint was reached was Sample 2 followed by Sample 5, and the lowest mean was Sample 1, which was significantly lower than all other samples. The endpoint of titration represents the point where enough acid has been added to react with all of the weak acid anions. Samples 2 and 5 were both seawater samples collected from different parts of the ocean. While samples 1 and 6 are both freshwater samples so this may be a potential cause for the seawater samples to have a higher concentration of weak acid anions present compared to the freshwater sample. Although outside knowledge confirms that freshwater usually has weak acid anion sources nearby, the retention pond may be collecting various pollutants bound to water upon redistribution, like sulfuric and nitric acids, that cause any weak acid anions present to be occupied neutralizing their hydrogen ions. It was expected the standard solution would have a high ANC because it contains bicarbonate anions, but the results infer all samples contained more weak acid anions. Since the samples were considered under the effects of acid rain, it can be inferred that Samples 2 and 5 would be most affected. This sample has the lowest ANC, and acid rain will lower the pH at a faster rate compared to the other samples. However, outside sources state acid rain does not always affect freshwater due to more soil, rock, and vegetation sources that neutralize the acid. The experimental outcomes support the hypothesis that states sea water will have a higher ANC compared to fresh water. 5 | P a g e

VI. Tables & Figures Figure 1: Experiential data for each water sample Figure 2: Representation of the calculated Mean and Standard deviations for each sample stan da rd deionized wat er boat basin pond water canal water mar ine salt wate r grou nd water 0 2 4 6 8 10 12 14 16 Water samples ANC calculated mean and standard devation Mean Standard Devation Water sample mL 6 | P a g e

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