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McGill University *

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110

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Chemistry

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Feb 20, 2024

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pdf

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Lab report, hand in within 48 hours Significant Figures • Save as .pdf file and submit to MyCourses or you will receive a 5% deduction. • Double check your submission to make sure that you have submitted the correct file. If you submit the wrong file, an empty template or a file that we are unable to open, you will be assigned a grade of 0. You may resubmit and your report will be marked with any relevant late deductions. Name: Yuna Jang ID #: 261135819 TA: Natalia Munoz Patino Lab Date and Time: 09/11/2023, 14:35-16:55 Questions 1. Is it possible for a volumetric pipette to have a high precision but low accuracy? How could this situation arise? (3pts) Yes it is possible. If a volumetric pipette is incorrectly calibrated or manufactured with poor measurement, this situation will arise. For instance, if the line on the pipette is manufactured to be slightly lower, the resulting values in each trial of the experiment will all cohesively display a lower, inaccurate pattern. In other words, if used with proper pipetting procedures, a pipette with incorrectly calibrated lines will lead to each trial replicating similar values, that are also all similarly far from the actual known value. 2. According to your results, what piece of glassware is the most precise? Is this what you expected? For the glassware that you expect to be the most precise, give three reasons why you think it should give the most precise results. (If you give more than 3 reasons you will receive a mark deduction) (3pts) The most precise piece of glassware, according to my results, is the pipette. Usage of the pipette resulted in the lowest relative standard deviation percentage of 0.58%. I expected this result for three reasons. First, since it is the most narrow, the meniscus is the smallest on the pipette. Therefore, I believed that a pipette would minimize the reading imprecision based on subjective estimates, allowing for greater reproductibility of results. Second, the process of pipetting requires the need for water to slowly be sucked up a narrow tube. When comparing this process to that of the other instruments, which require the action of pouring the liquid inside, I hypothesized that the pipetting technique minimized the error of trapped air bubbles inside of the liquid, and ultimately Lab report, hand in within 48 hours

Lab report, hand in within 48 hours would be the most capable of reproducing similar results with each trial. Third, a pipette is the only instrument where a liquid enters and exits through the same path. I hypothesized that this feature, unique to pipettes, minimizes the amount of liquid staying on the sides of the instrument, making the measurements of the transported liquid the most reproducable. Numerical results Distilled water Temperature of water (in °C): 23.8 From "constant" table on datasheet Theoretical density of water (in g/mL): 0.9973 Use Figure 4 in the lab manual to determine the theoretical density of water at the temperature you recorded.

Lab report, hand in within 48 hours Volumetric Flask Volume Mass Density Deviation (mL) (g) (g/mL) (g/mL) Trial 1 50.00 49.832 0.9966 0.0007 Trial 2 50.00 49.420 0.9884 0.0089 Trial 3 50.00 49.532 0.9906 0.0067 Average (mean) density (g/mL) 0.99189 Standard deviation (g/mL) 0.008 RSD (%) 0.79 Absolute error (g/mL) 0.0054 Relative error (%) 0.54 Pipet Volume Mass Density Deviation (mL) (g) (g/mL) (g/mL) Trial 1 10.00 9.908 0.9908 0.0065 Trial 2 10.00 9.930 0.9930 0.0043 Trial 3 10.00 9.948 0.9948 0.0025 Average (mean) density (g/mL) 0.99287 Standard deviation (g/mL) 0.006 RSD (%) 0.58 Absolute error (g/mL) 0.0044 Relative error (%) 0.44

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