Chemistry

Chemistry assignment

Complete the data table with the measured and calculated results.
Solution pH [H+] [X-]eq [HX]eq Ka pKa log{[X-]eq/[HX]eq}
1
2
3
4
5
6

 

Show a sample calculation for each column for trial 1 here:

 

Results:

1. Calculate the average value of pKa.

 

2. Graph the values of pH vs. log{[X ]eq/[HX]eq}. (Be sure to use proper graphing methods) Using a line of best fit, determine the value of Ka and pKa for your weak acid from your graph and record here. Staple the graph to the back of your report sheet. Compare this value to the value above.

 

Discussion:

1. Try to identify your weak acid using these pKa’s [Acetic Acid,4.74; Chloroacetic Acid, 2.85 ;Succinic Acid, 4.21; Hydrogen Phthalate Ion, 5.21; Formic Acid, 3.74]. How does your experimental value compare with the accepted value for your acid?

 

2. Without doing any calculations, indicate which of the five acids would give the highest [H+] in aqueous solutions of equal concentration. Explain your reasoning.

3. Our experience has been that the six pKa’s calculated from the pH data will vary somewhat in value. Should we expect the pKa, and hence the Ka, of a weak acid to vary with concentration? Defend your answer with a sentence or two of discussion.

 

 

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