Science Homework Help

Acidity Constant from a titration curve:

Fill in Data Table –

Table 1. Raw Data for the titration of HCL with NaOH

Concentration of HCl (M)	0.1028 M
Volume of HCl in Erlenmeyer Flask (mL)	10 mL
Concentration of NaOH (M)	0.1001 M
Initial Buret Reading (mL)	Final Buret Reading (mL)	Volume NaOH Added (mL)	PH
18.00	18.00		1.44
18.00	19.01		1.49
19.01	20.00		1.56
20.00	21.00		1.64
21.00	22.05		1.75
22.05	23.01		1.83
23.01	24.00		1.95
24.00	25.00		2.14
25.00	26.11		2.37
26.11	26.35		2.45
26.35	26.50		2.52
26.50	26.70		2.60
26.70	26.90		2.73
26.90	27.10		2.98
27.10	27.39		3.60
27.39 *PINK	27.59		9.72
27.59	27.73		10.90
27.73	28.73		11.76
28.73	29.73		12.03
29.73	30.75		12.24
30.75	31.76		12.31
31.76	32.81		12.33

Table 2. Raw Data for the titration of CH3COOH with NaOH

Concentration of CH3COOH (M)	0.1020 M
Volume of CH3COOH in Erlenmeyer Flask (mL)	10 mL
Concentration of NaOH (M)	0.1001 M
Initial Buret Reading (mL)	Final Buret Reading (mL)	Volume NaOH Added (mL)	PH
3.00	3.00		2.69
3.00	4.00		3.55
4.00	5.00		3.93
5.00	6.00		4.14
6.00	7.00		4.38
7.00	8.00		4.55
8.00	9.00		4.76
9.00	10.00		5.03
10.00	11.00		5.36
11.00	11.20		5.48
11.20	11.40		5.59
11.40	11.60		5.73
11.60	11.80		6.00
11.80	12.00		6.25
12.00 *PINK	12.20		8.62
12.20	12.40		10.87
12.40	13.40		11.85
13.40	14.40		12.10
14.40	15.40		12.29
15.40	16.40		12.36

Calculations –

–Theoretical Volume of NaOH needed to reach endpoint for both
HCl and CH3COOH

– The Acidity Constant (Ka) of HCl

– Percent Error of HCl Ka
■ Theoretical Value = 1.3 x 106

– The Acidity Constant (Ka) of CH3COOH
■ HINT: You can use pKa to find Ka

– Percent Error of CH3COOH Ka
■ Theoretical Value = 1.8 x 10-5

Results (make sure to look at the attachment below and complete those requirements as well) –

(include pictures of the graphs in excel as well as the excel attached because my excel is old)

Results: From the phenolphthalein endpoint, from calculation and from the titration curve,
estimate the pH and Veq at equivalence points for HCl and CH3COOH. Also, calculate Veq /2 (half
equivalence point) and pKa of acetic acid. (The lab text refers to Veq as V mL)

*There is no download for this experiment.

Your lab report should include the following in addition to the pages from your lab notebook:

 An Excel sheet “Raw Data” showing the volumes of NaOH vs HCl and NaOH vs CH3COOH.

Enter the numbers in the first spreadsheet from your lab notebook.

 A 2nd Excel sheet “Graph-HCl” showing the titration curve of HCl titration (solution pH vs
volume of NaOH). On the titration curve, mark the equivalence point and circle it. Draw
dotted perpendicular lines to the x and y axes. Estimate the pH and volume of NaOH added
at the equivalence point.

 A 3rd Excel sheet “Graph – CH3COOH” showing the titration curve of CH3COOH titration
(solution pH vs volume of NaOH). On the titration curve, mark the equivalence point and
circle it. Draw dotted perpendicular lines to the x and y axes. Estimate the pH and volume of
NaOH added at the equivalence point. Also calculate the volume corresponding to halfneutralization (Veq /2). On the graph, draw a dotted line perpendicular to Veq /2 until it
intersects the titration curve. Mark and circle the point and then draw a horizontal dotted
line which intersects the pH axis. This is the pKa of acetic acid.

■ Include 1-5 sentences that briefly summarize the procedure
and what information was obtained

■ Example:
– ____ g (or mL) of Reagent A were reacted with _____ g (or mL) of
Reagent B until a precipitate formed/gas evolved/color change
occurred. Observations were made and data were collected. Table 1
represents _____. Table 2 represents _____. Figure 1 represents
_____. Figure 2 represents ____.

Discussion –

■ Give a thorough interpretation of the results

■ Why is it not necessary to use phenolphthalein indicator to
detect the endpoint in this titration?

■ Can the pKa of acetic acid be calculated from the pH at a volume other than the half
equivalence point? Explain how.

■ What is the pH and the volume of NaOH added (VmL) at the equivalence point? Calculate the
pH at equivalence point using your experiment Ka, concentrations and volumes, and
compare it with your experiment pH. Find the percent error. What are some sources of
error that would account for this difference? BE QUANTITATIVE.

■ Explain why the weak acid-strong base titration equivalence
point is not at pH= 7.0.

■ What would the titration curve look like if the NaOH was
being titrated by the CH3COOH?
– Explain your answer.

■ Discuss the % Error. What is the major source of error?

Write a Conclusion –

■ Restate the purpose of the experiment

■ How did you attempt to meet the purpose?

■ Was the purpose met?

■ Restate the anticipated outcome. Was the actual outcome close to
the anticipated outcome?

■ Why or why not? What errors did you specifically experience in
this experiment?
– Distance-learning format of the class is not an error

■ What are some future improvements to this experiment?
– “Updating the lab manual”, “clear/better instructions on
how to perform calculations”, “instructor not explaining the
lab procedure”, “do not make the class a distance-learning
course”, etc. are NOT future improvements

(Lab manual pages 207-212)

Please ask me if you have any questions!