Visual Indicators Part 1 Procedure

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Feb 20, 2024

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Visual Indicators Name: Eliza Lannon Date: 10/04/2023 Group member: Yelnya Gonzalez

Visual Indicators Background: Acids and bases have been used for centuries – using the acid from lemons to cook fish in ceviche or using soap for cleaning purposes. We use a multitude of acids and bases during the course of everyday activities, for example in cooking, cleaning, and washing. Acids and bases have very different properties from each other. The ancient Greeks first attempted to define acids and bases and tell them apart based on taste, eventually leading to the word “acid” as we know it today. Early scientists later determined that sour-tasting substances changed the color of litmus and caused metals to corrode.¹ Bases were characterized as substances that react with acids and neutralize them. They were identified as bitter tasting and slippery to touch. “Alkaline” is a word associated with bases and is derived from Arabic word for roasting because the first alkaline substances were obtained by roasting ashes and treating them with slaked line (calcium hydroxide) to make two classic bases – potassium hydroxide (KOH) and sodium hydroxide (NaOH) – both of which are used to make soap.¹ According to the Arrhenius concept, an acid is a substance that produces H⁺ ions in solution and a base is a substance that produces OH‾ ions in solution. An acid and a base will react to neutralize each other and produce salt and water. pH is the expression of the dissolved H⁺ concentration: a pH less than 7 is considered acidic, pH of 7 is neutral, and a pH that is greater than 7 is basic.² Indicators are dyes and pigments isolated from variety of sources including plants, fungi and algae. Natural indicators are obtained by treating flowers/fruits/vegetables with a solvent to dissolve the soluble compounds. The color of an acid-base indicator is subject to change based on the pH of its immediate environment. Indicators react with an acid and/or base and change color based on whether an acid or a base is present. We can use this color change to predict if an unknown substance is an acid or a base. Different indicators change color over different pH ranges. Brassica oleracea , more commonly known as red cabbage, is useful as an acid-base indicator owing to the fairly wide range of pH related color changes. It contains water-soluble anthocyanins, which have indicator properties and vivid colors, making it easy to visualize color changes that occur when they are exposed to different pH conditions. When mixed in solution with acid it turns pink; when mixed with a base it turns a blue; with stronger bases, the color is a lighter yellow; and it stays the same color when mixed in a solution with a neutral pH. References: ¹ BBC. (2010). The History of Acids and Bases . www.bbc.co.uk/dna/h2g2/A708257. ² Burdge, J. (2013). Chemistry. 3rd. McGraw Hill.

Visual Indicators The scenario is that this lab is the research and development department for a company that produces chemicals. Upper management wants us to determine if an acid-base visual indicator can be made from another substance besides Brassica oleracea . They would like us to: 1. Make 400mL of indicator using another substance besides Brassica oleracea (red cabbage) and determine its effective pH indicating range. —and— 2. Make 400mL of indicator using Brassica oleracea and compare its effectiveness to the novel indicator made from a new substance. We have been supplied with the instructions to produce Brassica oleracea indicator: 1. Boil 400mL of water. 2. Once the water is boiling, add 3-4 leaves of the cabbage (approximately 60- 80g). 3. Allow the red cabbage leaves to boil in the water until the water changes color. 4. Once the water turns blue, transfer the liquid to another container, filtering out the solids. The indicator is ready for use with acids and bases. Take 5-10 minutes to discuss with your team how you will tackle the two tasks. Typically, for an indicator to react well, the amount of visual indicator used must equal the amount of substance (unknown acid, base, etc.) being tested. Keep in mind that we have substances ranging from acidic to basic and we have pH paper at our disposal. Once you and your team are in agreement and you have discussed your plan with your TA, write out the steps you plan to follow and begin working. The procedures should be written so that they can be accurately replicated by other researchers. Take pictures of the indicators before use and after. Once the data has been collected and observations have been documented, report your findings. In addition to comparing and contrasting the two indicators, discuss limitations and sources of error, things scientists who are replicating your procedures should consider modifying, and any areas of future study you believe are relevant. Safety precautions: • Never mix ammonia and bleach, as the reaction produces hazardous gases. • Mixing unknown chemicals together is dangerous. Only mix an unknown substance with your indicator and not another unknown substance. • Keep the volume of acid/base at or below 10mL for every trial. One should never be transporting large volumes of dangerous chemicals. • Wear protective goggles, a long sleeved shirt, and long pants at all times. • Be mindful of the surfaces of hot plates. Only transfer boiling beakers when holding mittens. • Label containers. An unknown acid without a label might be mistaken for water.

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Visual Indicators Supplies: • Brassica oleracea (red cabbage) • Glassware • Hot plate • pH/Litmus paper • Acidic substances • Basic substances Procedures: - Gather Materials: Hot Plate, corresponding cord, one 500 mL beaker, four 50mL beakers, transfer pipettes, cabbage, empty water bottle, various testing liquids( HCl, CH3OOH, NH4OH, Aspirin, NaHCO, Coke, Bleach, NaOH, Sugar and H2O, NaCl, Tums) - pour 300 mL of water into your 500 mL beaker and put to boil no max capacity heat. - once boiling take three to four pieces of cabbage and places then into the boiling water. - once you see a blue color taken on from the cabbage (this is your indicator fluid.) transfer the water into four separate 50mL beakers using the transfer pipettes. - pour 30 mL of the indicator fluid into each beaker then pour your different test fluids into each beaker. - wait to see the mixture to change color. Record the color. - use pH indicator papers to assess the actual pH of the different test fluids. Record the color and corresponding number. - add the data to your table, then make an assessment as to whether the pH indicator liquid. - record all your data, clean your area and complete post lab accordingly.

Visual Indicators Data & Observations: Chemical substance Color of reaction with Cabbage Indicator Number and color of pH paper HCl red 4 orange CH3COOH pink 1 pink NH4OH green 8 green Asprin pink 5 gold NaHCO teal 8 green Coke purple 6 yellow Bleach yellow 9 dark green NaOH yellow 12 navy blue Sugar and H2O Purple 5 gold NaCl blue 6 yellow Tums light blue 7 light green Post-Lab questions: Address and answer these questions as a part of your discussion on the following page. 1. What color range did you observe with the red cabbage indicator? The range included the entirety of the rainbow with the exception of orange, this was due to the range in acidity that caused the change in color in the red cabbage indicator. 2. Did the visual indicators and pH/litmus paper give you consistent results? Meaning, if the visual indicator implied a substance was acidic, did the result of the litmus paper agree? Summarize your results and justify them with evidence. Each substance was relatively reasonable in terms of correlation between the pH paper and the red cabbage pH indicator. So generally, they show consistent results. For example, liquids like HCl and CH3COOH, which are known acids, are shown to be acidic by both methods (pH paper and red cabbage liquid). Substances like NH4OH and NaOH, known bases, are indicated as basic by both methods. Tums (a base) is identified as neutral in conjunction with both indicators. The variation in the reading/data for both methods can be attributed to the fact that different indicators may produce slightly different color changes.

Visual Indicators Discussion: In this laboratory experiment, we conducted a comprehensive investigation into the properties of the red cabbage indicator as a tool for assessing the pH levels of various substances. Our findings were summarized and evaluated. We observed that the red cabbage indicator display a large range of color, and we determined the consistency between the visual indicators provided by the red cabbage solution and the pH/litmus paper. Potential sources of error in this experiment encompass the imprecision in measuring while pouring water into the larger beaker, transferring the indicator liquid into the smaller beakers, and adding the test liquid to the indicator solution. Another possible error relates to the approximations we made when recording data, including both the numerical values and the observed colors from the pH paper. Addressing these potential sources of error in future experiments can enhance the accuracy of our results. One effective remedy involves using graduated cylinders to ensure precise measurements during liquid transfer processes, thus providing more reliable pH readings for the indicator solution. However, it's important to note that addressing the potential for error associated with pH paper readings may prove challenging unless we gain access to more advanced and accurate equipment capable of directly measuring the actual acidity of the mixture.

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