Unit 1 Lab.pdf - Observing and Inferring | Semester 1 Unit...

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Unformatted text preview: Observing and Inferring | Semester 1, Unit 1 LAB 1: OBSERVING AND INFERRING NOTE TO STUDENTS: This is a dry lab. You are only expected to perform the portions of this lab that do not require you to use laboratory equipment or supplies. When appropriate, sample data may be supplied in the lab’s data tables to help you answer the questions. WITH EXTENSION While inferences are in a way, an educated guess, they can be used to help guide us You are already an inference maker. The goal into greater scientific truth. In this lab, you will exercise and of this lab is to show you how to formalize refine your already innate ability to your inferences make inferences into the unknown. Your inferences will be grounded in known Materials and Equipment information, and guided by science. Goals 0.1M HCl (an acid) 0.1M KOH (a base) Bromothymol blue (BTB) Goggles Ruler with mm markings Procedure Materials Not Included First, you will be seeing how a drop of each of the reagents wicks through paper. SAVE THE PAPER TOWEL USED IN EACH STEP FOR LATER STEPS. 1. Fold a white paper towel so that it is four layers thick and flatten it. Paper towels Introduction Inference (noun): A conclusion reached upon the basis of evidence and reasoning. Synonyms: Deduction, conclusion, reasoning, conjecture, speculation, guess, presumption, assumption, supposition, reckoning, extrapolation. Everyone often uses inferences. If someone comes in from outside and is all wet, you might infer that it is raining outside. You see a trash can rolling down the road and you might infer it is windy outside. Sometimes we use inferences to predict something. For example, you see dark rolling clouds. You might infer that it is going to rain. if you see the numbers 2, 4, 6, and 8, and you had to infer what number would come next in the pattern, you would predict 10. Inferences are even used in the sciences. For instance, a meteorologist (scientist who studies weather and climate) might gather data and, based on that data, and infer there is a high chance of rain. 2. Drop 1 drop of acid (0.1M HCl) onto a paper towel, wait one minute, then measure how far it wicked out into the paper towel. Record the diameter of the drop in Table 1.1 in mm. 3. Repeat Step 2 but use a drop of base (0.1M KOH) instead. 4. Repeat Step 2 but use a drop of bromothymol blue (BTB) instead. NOTE: This is a solution of 99.96% water and 0.04% BTB. a. When you measure the diameter of the BTB drop, you will notice that the BTB color is not evident out as far as the liquid wicks. That is, it appears that the BTB is retained by the paper while the water is relatively free to keep wicking outward. Record (in Table 1.1) both the total diameter of the wet spot and the smaller diameter of the BTB-colored Copyright © 2017 Quality Science Labs, LLC 1 Apex Learning: Chemistry Labs Table 1.1 Reagent Diameter that 1 drop of liquid wicked Acid (HCl) 21 mm Base (KOH) 23 mm Diameter BTB’s color wicked Bromothymol blue (BTB), 0.04% 20 mm region within the wet spot. b. Also, record what happened to the color of the bromothymol blue as it remained on the paper in contrast to its color in the bottle. Second, you will see what happens when BTB is added to the drop of acid or base. 1. To your drop of acid that wicked into the paper towel, add 1 drop of BTB. Record the color in Table 1.2. 2. To your drop of base that wicked into the paper towel, add 1 drop of BTB. Record the color in Table 1.2. Third, you will see what happens when your previous acid plus BTB drop and base plus BTB drop have acid or base added to them respectively. 10 mm Yellowish blue Fourth, you will see what happens when the drops merge on the paper towel. 1. Fold a new piece of white paper towel so that it is four layers thick and flatten it. 2. You will drop a drop of acid and a drop of base side by side on the paper towel such that they will wick close to each other. Use your previous diameter measurements to determine how close you should place these drops. 3. Next, drop a drop of BTB directly in between the drop of acid and the drop of base, and begin observing color changes. Record these initial color changes and the stagnant colors. You have space for only five observations in Table 1.4, so pick your favorite five. 1. To your drop of acid plus a drop of BTB (currently a colored spot on the paper towel), add 1 drop of base. Record the resultant color in Table 1.3. 2. To your drop of base plus a drop of BTB (currently a colored spot on the paper towel), add 1 drop of acid. Record the resultant color in Table 1.3. 2 Color of BTB as it remained on paper Copyright © 2017 Quality Science Labs, LLC nothing Observing and Inferring Table 1.2 Observation Color of BTB drop on previous acid drop is: Yellow, but not all the way out __________________________________ Color of BTB drop on previous base drop is: Blue __________________________________ Color of drop of BTB while still in the bottle is: Blue __________________________________ Color of BTB on paper is: Yellowish blue __________________________________ Your inference (sample inference ) BTB in the presence of acid is colored Yellow. ______________________ BTB in the presence of base gets bluer and colored completely blue rather than yellowish blue. The paper that the BTB was dropped on is what makes the color look yellowish blue. There is some sort of colorant or product in the paper that changes the blue BTB into yellowish blue. Table 1.3 Observation Color when a drop of base is added to previous acid plus BTB spot: Blue __________________________________ Color when a drop of acid is added to previous base plus BTB spot: Yellow __________________________________ Your inference about what happened The base changes the yellow BTB plus acid back to the original color the BTB, blue. The acid bleaches the blue BTB plus a base and turns it yellow. Table 1.4 Observation Your inference about what happened Where drop of BTB wicked into acid the color is bright yellow. The BTB exaggerates the effects of the acid making it more yellow than it was when the acid came after the BTB. Where drop of BTB wicked into base the color is bright blue. The BTB exaggerates the effects of the base making it more blue than it was when the base came after the BTB. The region where the BTB wicked into the base was larger than the region it wicked into the acid. The base’s capabilities at making the colors spread further is stronger than the acid’s capabilities. Copyright © 2017 Quality Science Labs, LLC 3 Apex Learning: Chemistry Labs LAB 1 Questions for Observing and Inferring 1. For this question use the necessary data from Table 1.1. Even though you don’t know the absolute concentration of the BTB on the paper towel as it wicks out, you can graph its relative concentration. Assume that the highest concentration of BTB is at the center of the drop. For convenience, call this highest concentration “100” and call the concentration at the drops outermost edge “0”. (You do not need to assign units, because the concentrations you are graphing are relative concentrations.) Text a. Draw a graph that shows the relative concentration of BTB from the center of the Check with the drop to the edge of where the paper was wet. example graph See sample graph below question 3 below. b. In the above graph, did you have the concentration go to zero when you could no longer see BTB? Or did you assume BTB was still there albeit at invisible levels? The graph has the BTB concentration at zero. The BTB is heavily colored and will affect the look of white paper if it is truly present. The colors fade as the concentration disappears. Further, this experiment is about wicking so if there is no movement in the paper, one knows it is gone. c. Shade in the portions of both graphs where you were making assumptions (saying things you have no evidence for) about the concentration of BTB. 2. From your data, could you infer that the paper towel is acidic? Explain. You could certainly assume that the paper towel is acidic because it changed the color of the BTB when it touched it. When acid touched BTB it changed it from blue to yellow. When BTB touched the paper towel alone it became a yellowishblue. Therefore, the paper towel has acid in it, although probably not that much since the color didn’t change drastically. 4 Copyright © 2017 Quality Science Labs, LLC You could certainly assume that the paper towel is acidic because it changed the Text Text Text Observing and Inferring 3. How could you prove that your inference about the acidity of the paper is true? You could prove that the paper is acidic my comparing how acid affects other products and see if the paper towel had a similar effect. We see that the paper towel affected the BTB in a minor way that was similar to the acid in that they both turned yellow. If the same type of thing happens with other products, then you know there is at least a little acid in there. Copyright © 2017 Quality Science Labs, LLC 5 ...
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