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12 Dec 2019

I am writing a lab report over the the spectroscopic determination of an acid/base indicator's pKa value.

I need help with the following quesions......

1. What factors could contribute to the inability of an analyst to obtain an isobestic point.

2. If the molar absorptivities of HInd- and Ind2- were determined at the isobestic point, how would they compare?

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I NEED HELP ANSWERING QUESTION 4 AND 5!!

Experimental Determination of pKa of buffers In this lab you. the student, will titrate several different buffer solutions in order to determine their pKa. Recall from class that (or from the water chemistry chapter of your textbook) that the pKa of a weak acid/base is equal to the pH of the solution when it population of molecules are 50% protonated/deprotonated. In this lab you will be given a butter solution (typically at low pH) and will titrate with 1 M potassium hydroxide (KOH) while measuring the pH during each stage of the process. You will then need to generate from your data a titration plot and then to extrapolate from there the pKa of the weak acid/base. General Procedure Tentative buffers to be tested: water (N = 1), 0.4 M Acetic Acid (N = 3), 0.4 M Glycine (N = 3), [N is the number if replicates] As in any lab put on your personal protective equipment (PPE): lab coal, safety glasses, and gloves Setup burette with 1 M KOH. Be careful not to spill. In a small beaker (100 mL or smaller) pour in 40 mL of buffer to be tested. Titrate until pH passes 12. Be consistent with your dispensing of KOH so your replicate trials line up appropriately. Tabulate and graph data (use formatting that is consistent with Lab 1 and include standard deviation in tables and graphs) Questions and concepts to address in the lab report Describe the buffering capacity of water based on your titration. How do they compare to Acetic Acid and Glycine? For Acetic Acid and Glycine Buffers: For titrations with N = 3. how can you account significant differences between data points? What were the pKas of your buffers based on your titration? How do they compare to those reported in the literature? How do you account for difference in values? Draw the three possible ionic forms of each buffer. Identify which of these predominates at pH 1, pH 6, and pH 11. What are the chemical equations that show how each buffers solutions at either pKa by consuming amounts of added hydrogen or hydroxide ions.

separation of a three-component mixture by extraction, labreport help, the compounds are benzoic acid ,9-fluorene , andethyl-4- aminobenzoate. I need help to write Discussion about thislab report and I dont know what should I write.I got 25% recovary for benzoic acid ,32%for ethyl-4- aminobenzoateand 50 % recovary for 9-fluorene.( by the way I lost some product ofbenzoic acid). please help me full paper as you could fordiscussion and what is the source of error and how we couldimporove the lab. also I attached the procedure of lab report maybe help out.

http://risk.management6.com/Separation-of-a-Three-Component-Mixture-by-Extraction-download-w12001.pdf

the melting point which I found for benzoic acid is 126-129 C,

ethyl-4- aminobenzoate : 89-92 C

9-flourene : 49-51 C

and for the mix of crude is 59-71 C

some information about Discussion:

Discussion: The purpose of the discussion is to interpret andcompare the results. For this section, list all the importantfactual information that you obtain from the experiment and thendiscuss these factual results. For example, report the experimentalmelting point, % recovery or % yield, etc and then compare thiswith the literature value and derive a conclusion from this result.For some of the experiments, your instructor might indicate a focusof the discussions. The discussion may also answer the followingquestions:

Need help trying to do a Titration lab, for example:

Say you were to start with 0.209 grams of an unknown acid. You then transferred that into 20 mL of water. Took that flask of 20 mL of water and 0.209 grams of the unknown solution over to a burette that contains 0.112 M of concentrated NaOH solution. To get to the endpoint of the titration, I dispensed 9.12 mL of the base. I then hovered over the midway point of the titration, and had 5.4pKa and 4.7 mL

then repeated the same steps for the same unknown weak acid, this time I used 0.201 grams, and again transferred it into 20 mL of water which I then titrated with the 0.112 M of concentrated NaOH solution. It took 8.90 mL of base to reach then endpoint and had values of 5.42 pKa and 4.54 mL.

Question #1:

Calculate the moles of OH required (be careful to convert the mL of base to L of base in this calculation)

mol base for trial #1 = __________mol

mol base for trial #2 = __________mol

Question #2

calculate molar mass of weak acid for each trial

g/mol for trial #1 = ___________ g/mol

g/mol for trial #2 = _________g/mol

average for 1 and 2 = ___________g/mol

Third question:

Determine Ka value for weak acid from both trials

Formula = Ka = 10^-pKa

*Use "e" notation such as 1.25e-5.....DO NOT USE 1.25X10^-5

Ka for trial 1 = __________

Ka for trial 2 = ________

Ka for trial 3 = _________

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