Name Formal Lab Assignment # 2 (12 pts) assignment independently. In this assign
ID: 916084 • Letter: N
Question
Name Formal Lab Assignment # 2 (12 pts) assignment independently. In this assignment, you will demonstrate to draw conclusions about the identity of an unknown acid. This your You must complete this ability to use laboratory t ty to use laboratory data to draw conclusions re-lab the week of November 16h. Late assignments may be assignment is due at the start of p turned in up to a week after the original due dato. Late assignments Instructions: 1. Re-read exporiment 10 in your lab manual 2. Read the following scenario. will be penalized 4 pts. 3. Using the data given in the scenario and the attached titration curve, complete a curve. complete and show any necessary calculations in the space provided on the back of this sheet. 4 Using the data and results for the scenario, identify the unknown acid from the table given on the back of this sheet On a separate sheet of paper, neatly and legibly write a conclusion paragraph that identifies your unknown acid and cloarly explains how you used your data and results to identify your compound. This paragraph should repeat important results/data for your unknown and discuss how you excluded other possible compounds. It should not include calculations and it should not include lab procedures. Remember that a well supported conclusion should include the following 5. An introductory sentence that explains what you were trying to accomplish and how you achieved it .One or two sentences that describe how one data point for your unknown was used to narrow down the list of possible acids. These sentences should give the experimental value for the unknown as well as the names and accepted values for the possible acids that have made it to the "short list" of compounds to consider. so, but it is not mandatory in most cases. One or two sentences that describe how you used each subsequent experimental value for your unknown to identify it. You should report the value and describe how it compares to the accepted values for the possible acids from your "short list." accepted values. in most cases You may report % differences if you choose to do . Make sure you give those You may report 96 differences if you choose to do so, but it is not mandatory You should always use and discuss all relevant experimental data to which you have access in your conclusion. A conclusion sentence that clearly identifies your unknown. . 6. I should be able to read this paragraph without looking at any other part of the assignment and be convinced that your conclusion is correct Scenario: A student titrated a 0.366 g sample of an unknown acid using 0.100 M NaOH. The following titration curve was generated using data from the titration. Using this information, identify the unknown acid from the table of possible unknown acids. (Note: This acid is NOT necessarily the same as the one you used in experiment 10.)Explanation / Answer
5.
a.From the provided experimental data it possible:
-to estimate the identity of the unknown acid (qualitative assessment)
-to calculate the molar mass of the unknown acid (quantitative procedure allowing to identify without doubt the acid)
b.
If the pHmeter used to monitor the titration was well calibrated, then the pH value at EP/2 is indicative for pKa of the titrated acid. This value is pH= 4.9. There are 4 candidates in the list, having pKa in the range 4.5…5.3. They are…..
The calibration curve is also an evidence that the acid is monoprotic (only one pH jump, final pH is >12)
c.
VEP = 60 mL
0.100 mol/L x 0.060 mL = 0.006 mol NaOH used also 0.0060 mol of the titrated acid
0.366 g acid / 0.0060 mol acid = 61 g/mol , the acid molar mass.
d.
Looking at the list, the best candidate is Acetic acid
-pKa = 4.75
-monoprotic
-molar mass 60
These informations are in agreement with the experimental data, accepting some errors.
e.
Conclusion : the unknown is identified as acetic acid.
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