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Lab 1 Report FORM How Do We Make Accurate and Precise Measurements of Physical Properties Sp23
General Chemistry for Engineers (CHM 115)
Purdue University
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Lab 1: How Do We Make Accurate and Precise
Measurements REPORT FORM
Answer the following discussion questions. Support your claim using evidence, i. experimental
data that supports the claim. Cite specific quantitative results. Connect your evidence to your
claim using reasoning that explains why your evidence supports your claim. Reasoning should be based on a scientific rule, law, principle or definition.
To answer these questions, you will need to calculate the following: - mass of water for all trials, - volume of water for all trials, - mean absolute deviation for each measurement device, - percent error for each trial and - average percent error for each measurement device. Your data and these calculations will make up the quantitative results you will use to support your answers to the report questions. It is recommended that you write out at least one calculation and make note of your calculation results in your laboratory notebook for future reference. Laboratory material is also included in exam content and these can be useful materials for studying for the exams.
To determine accuracy, we calculate the error or the percentage error using the calculated and theoretical values of volume. If we are trying to measure 10 ml of water using an instrument, the theoretical value is 10 and the experimental value is what we obtain when we divide the mass of the measured fluid by the density of that fluid. (volume = mass/density) From the calculations, the 10 mL pipet has the greatest accuracy although the 50 mL burette has a percentage error close to that of the pipet. The 10 mL pipet has a calculated percentage error of 0.
[(9 – 10)/10 * 100] Where 9 mL is the calculated volume based on the measured mass, temperature, and density. Note that the final value should be a positive number which means the difference between the theoretical and experimental volumes should be calculated as an absolute value.
Question #1. Which calculation or value provides you with an indication of the accuracy of
the glassware? Which piece(s)has/have the greater accuracy, the 10-mL graduated cylinder, 50-mL graduated cylinder, 50-mL burette, or 10-mL pipet? Provide an example for the calculation or value and explain using your quantitative results.
Question #2. Which calculation or value provides you with an indication of the precision of
the glassware? Which piece(s) of glassware has/ have the greatest precision for measuring volume: the 10- mL graduated cylinder, 50-mL graduated cylinder, 50-mL buret or 10-mL pipet? Provide an example for the calculation or value and explain using your quantitative results.
The MAD value is a good indicator of precision. MAD stands for mean absolute deviation and it tells us how much each data point deviates from the calculated average. (We can explain this with the arrow and target analogy where the MAD tells us how far each arrow is from the rest of the arrows.)
Based on the calculations, the Burette and the Pipet had the lowest MAD value of only 8-2 and 3-2 respectively. (Based on observations from the lab, this checks out as the burette was the easiest to adjust in terms of dispensing volume into the flask.)
The 50mL cylinder had the greatest MAD which would indicate that the data deviates the most and the 50mL cylinder is therefore the least precise instrument of the 4 instruments used. (The MAD value of the 50ml cylinder was calculated to be 3-1.)
The three volumes calculated for the Pipet were: 9, 9 and 9 and the average volume was calculated to be 9. This means that the MAD value equals the sum of the difference of each of the 3 volumes with the average volume all over 3.
MAD = [abs(9 - 9) + abs(9 - 9) + abs(9 - 9)]/3 = 3-
Question #6. Recalculate the percent error of the glassware using the combined data from
you and the two other groups. What can you say about the difference in accuracy between your measurements and the combined measurements of the three groups? Has the accuracy changed? Explain using your quantitative results.
After recalculating the MAD values, it became apparent that there was a trend of low precision for the 50mL cylinder. My group calculated the MAD value of the 50mL cylinder in flask 2 to be 3-1 and after calculating the average MAD with the data from the other groups, the MAD for the flask 2 (50mL cylinder) was still the greatest at 2-1. This means that it is safe to assume that the 50 mL cylinder is the least precise measuring instrument of the 4 instruments used in the lab.
Precision of flasks 1 and 4, the 10mL cylinder and the pipet remained relatively same with only minimal differences. The precision in flask 3, the burette, seemed to have changed from a MAD value of 8-2 to a value of 1-1 which would indicate that the other two groups found the burette less precise as their data deviates a lot more on average. That being said, the two other groups also found the pipet to have the least MAD and therefore the greatest precision.
After recalculating the data, it became apparent that the mean percentage error for each flask decreased except for flask number 4 which indicates that the other two groups managed to minimize most of their percentage errors and were measuring their water with more accuracy.
The flask number 4 had an increase in percentage error from 0 to 0. This was mainly because the two other groups had relatively high percentage uncertainty for the pipet measurements. To be exact, their percentage errors for the pipet were 0 and 0 whereas our percentage error for the pipet measurements were 0. The percentage error in the 50-ml graduated cylinder decreased quite drastically as my calculations indicated that the percentage error was 15 but after recalculating with the other two groups the average percentage error for the cylinder came down to 7.
After recalculating, it can be said that the flask with the least percentage error is flask number 3 (the burette) and the flask with the greatest percentage error is flask number 2 (50 mL cylinder). The pipet, flask 4, actually has the 3rd greatest percentage error which is even bigger than the error in flask number 1. This is a surprising finding as I did not expect the pipet to be statistically less accurate than the 10mL cylinder (Flask 1).
Question #7. If you went back in time to repeat the measurement for the Hubble Space
Telescope, what measure(s) would you use to ensure the correct thickness of the mirror? Explain your reasoning.
In order to ensure the correct thickness of the mirror, I would focus primarily on the accuracy as opposed to the precision if there were a trade off between the two. It’s important to keep in mind that accurate results might not be precise enough or precise results might not actually be accurate at all.
I would probably try to calculate the percentage error and mean average deviation of the measuring techniques and instruments used to determine whether the thickness of the mirror is correct or should be measured again using a different technique. I would find the accuracy and the precision of each measuring technique and then I would evaluate which technique of measurement has both great accuracy and great precision relative to the rest of the measuring techniques/instruments used.
Lab 1 Report FORM How Do We Make Accurate and Precise Measurements of Physical Properties Sp23
Course: General Chemistry for Engineers (CHM 115)
University: Purdue University
Recommended for you
Students also viewed
- CHM 115 - part 2 - CHM 115 - part 2 - Chemistry: the Molecular Nature of Matter and Change
- CHM 115 - part 3 - CHM 115 - part 3 - Chemistry: the Molecular Nature of Matter and Change
- CHM 115 - part 1 - CHM 115 - part 1 - Chemistry: the Molecular Nature of Matter and Change
- CHEM 115 Final Notes
- Exam 3 (Ch. 9-10 Notes) - Purdue FYE CHEM 115
- Chapter 12 Notes - Purdue FYE CHEM 115