Instructions 1. Re-read experiment 10 in your lab manual. 2. Read the following
ID: 879097 • Letter: I
Question
Instructions 1. Re-read experiment 10 in your lab manual. 2. Read the following scenario. 3. Using the data given in the scenario and the attached titration curve, complete and show any 4. Using the data and results for the scenario, identify the unknown acid from the table given on 5. On a separate sheet of paper, neatly and legibly write a conclusion paragraph that identifies necessary calculations in the space provided on the back of this sheet the back of this sheet. your unknown acid and clearly explains how you used your data and results to identify your 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 compound. This paragraph should repeat important results/data for your unknown and discuss include the following .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. You may report 96 differences if you choose to do 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." Make sure you give those accepted values. You may report 96 differences if you choose to do so, but it is not mandatory in most cases. 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 0.576 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, i 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
KNOWN FACTS:
Nature of the titration curve for the titration of a strong acid with a strong base.:
In the titration of a strong acid with a strong base, the pH will change only very slowly at first and rise from 1 to only about 4. At the end point, the pH will rise suddenly from about 3 to 7 when the solution becomes neutral. Further addition of small amount of the strong base will make the pH jump to a vlue above 9
Nature of the titration curve for the titration of a weak acid with a strong base.
In this type of titrations, the vertical portion does not begin until beyond pH 7 and the end point lies somewhere between 8 and 10.This is due to the hydrolysis of the salt of the weak acid and strong base.
EXPERIMENTAL RESULTS:
From the titration curve,it is seen that the pH changes only very slowly at first and near the end point ,the titration curve is almost vertical and there is a rapid change of pH from 4 to about 11.
DISCUSSION:
The experimental results support a strong acid and immedately rule out weak acids like Acetic acid, Hexanoic acid, Octanoic acid , carbonic acid, Maleic acid,Oxalic acid,Tartaric acid, Arsenic acid, phosphoric acid and Boric acid.
More over, the titration curve of polyprotic acids will have more than one end point -
2 end points for diprotic acids ( Acids with 2 pKa values) like Carbonic acid,Maleic acid,Oxalic acid and Tartaric acid,
and 3 end points for triprotic acids ( Acids with 3 pKa values) like Arsenic acid ,Boric acid and phosphoric acid.
Since the titration curve shows only one end point, all these poly protic acids are ruled out.
This leaves only Chloroacetic acid which is a monobasic strong acid .This explains the sharp rise from 4 to 11
THE POSSIBLE UNKNOWN ACID IS THEREFORE CHLOROACETIC ACID