Grace Uditsky (40283842)- CHEM 271 Lab 1

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Grace Uditsky 40283842 Lab Section: 54 Date of Experiment: 22 January 2024

Uditsky, 1 Questions Part 1 - Use of Micropipettes 1. What are your absorbance values from the measurements at 410 nm? Table 1: Absorbance (at 410 nm) of three test tubes with 2.4 ml of 0.01M Glycine buffer and 0.1 ml of 0.35M p -nitrophenol. Test tube Absorbance (410 nm) 1 0.2388 2 0.2265 3 0.2266 2. What absorbance values did you get using increasing volumes of p -nitrophenol? Table 2: Absorbance (at 410 nm) of four test tubes with increasing volumes p -nitrophenol and decreasing volumes of 0.01M Glycine buffer. Test tube Glycine buffer (ml) p -nitrophenol (ml) Absorbance (410 nm) 1 2.3 0.2 0.4206 2 2.3 0.2 0.4091 3 2.1 0.4 0.9311 4 1.9 0.6 1.3385 3. Do tube #1 and tube #2 have the same absorbance? Should they have the same absorbance? Test tubes 1 and 2 do not have the exact same absorbance, however they should have the same values. Absorbance measures the amount of light absorbed by a solution. Since test tubes 1 and 2 have the same concentration of buffer and p -nitrophenol they should absorb the same amount of

Uditsky, 2 light, and therefore should have the same absorbance. The actual absorbance values of test tubes 1 and 2 are extremely close but not exactly the same. This could be due to unexpected errors during the experiment. Part 2- Kinetics of hydrolysis of p -nitrophenylacetate 1. Show your calculations to prepare all the p -nitrophenylacetate solutions starting from the stock solution. M 1 V 1 = M 2 V 2 1. 10 mM (x ml) = 0.05 mM (5 ml) x = 0.025 ml 5 ml - 0.025 ml = 4.975 ml add 0.025 ml of 10 mM stock solution and 4.975 ml water 2. 10 mM (x ml) = 0.10 mM (5 ml) x = 0.05 ml 5 ml - 0.05 ml = 4.95 ml add 0.05 ml of 10 mM stock solution and 4.95 ml water 3. 10 mM (x ml) = 0.25 mM (5 ml) x = 0.125 ml 5 ml - 0.125 ml = 4.875 ml add 0.125 ml of 10 mM stock solution and 4.875 ml water 4. 10 mM (x ml) = 0.5 mM (5 ml) x = 0.25 ml 5 ml - 0.25 ml = 4.75 ml

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Uditsky, 3 add 0.25 ml of 10 mM stock solution and 4.75 ml water 5. 10 mM (x ml) = 1.5 mM (5 ml) x = 0.75 ml 5 ml - 0.75 ml = 4.25 ml add 0.75 ml of 10 mM stock solution and 4.25 ml water 2. Can you use serial dilution? Explain how. A serial dilution cannot be done in order to obtain the desired concentrations in the laboratory manual. This is because in each test tube a different amount of 10 mM p-nitrophenylacetate is required. A serial dilution can only be done if the same amount of p-nitrophenylacetate was needed in all the test tubes. 3. Plot the rate of reaction vs [ p -nitrophenylacetate]; you should get a straight line. Graph 1: Reaction rate of p-nitrophenylacetate and 0.01 M Glycine buffer versus the concentration of the p-nitrophenylacetate solutions

Uditsky, 4 Table 3: Reaction rate of various concentrations of p-nitrophenylacetate when mixed with 0.25 ml of Glycine buffer. Test tube Amount of 10 mM p-nitrophenylacetate added (ml) Amount of water added (ml) Concentration (mM) Reaction rate 1 0.025 4.975 0.05 0.003775016 2 0.050 4.950 0.10 0.009684493 3 0.125 4.875 0.25 0.01865202 4 0.250 4.750 0.50 0.04424049 5 0.750 4.250 1.50 0.09041885 Results Part 1: Use of Micropipettors - See Table 1 (page 1). - See Table 2 (page 1). Part 2: Kinetics of hydrolysis of p-nitrophenylacetate - See Graph 1 (page 3). - See Table 3 (page 4). Sample Calculations Part 2: Kinetics of hydrolysis of p-nitrophenylacetate - How to calculate dilutions (M 1 V 1 = M 2 V 2 ) 10 mM (x ml) = 0.05 mM (5 ml) x = 0.025 ml 5 ml - 0.025 ml = 4.975 ml add 0.025 ml of 10 mM stock solution and 4.975 ml water

Uditsky, 5 Prelab

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Uditsky, 6

Uditsky, 7 References - J. Powlowski, M.J. Kornblatt, P. Joyce, L. Sahlman, J. Turnbull and Mihai Ciortea. Chemistry 271 Laboratory and Tutorial Manual, (Version 1.18), Concordia University Dept. of Chemistry and Biochemistry, 2023, pages 53-58.