Studying the properties of Buffer Solution PDF

Preview

Summary

Studying the properties of Buffer Solution - lab report...

Description

Studying the properties of Buffer Solution

SCC-202 – 633B Lab #7 Date: November 7th, 2019

Objectives The objective of this experiment was to prepare a buffer solution; study and analyze how well the buffer solution resisted to changes to its’ pH and compared it to the changes in an unbuffered solution.

Material            

0.10M Acetic Acid Sodium Acetate 0.10M NaOH 0.10M HCl Distilled water 100mL beaker 50mL Graduate Cylinder 25mL Graduate Cylinder 10mL Graduated Cylinder 100mL Beaker Dropper pH meter

Procedure Part I: Preparation of Buffer Solution 1. Obtain 50.0mL 0f 0.10mL acetic acid a. 75mL of 0.10M acetic acid was added to 100mL beaker with the use of a graduated cylinder.

b. A 50mL graduated cylinder was filled to the top mark with the sample previously collected. 2. Determine how many grams of sodium acetate are needed to make the buffer a. The moles of 50.0mL of acetic acid were calculated. b. The number moles of sodium acetate obtained in the previous step was converted to grams. c. A 100mL beaker was obtained and the sodium acetate calculated in the previous step was transferred. 3. Make and test your buffer solution a. The 50.0mL of acetic acid from the graduated cylinder was transferred into the “Buffer Sample” beaker and stirred until the sodium acetate was fully dissolved. b. The electrode was thoroughly rinsed before measuring the pH. c. The 50mL graduated cylinder was rinsed and dried. Part II: Study of Buffer Solution Properties 4. Two empty 50mL beakers were labeled as “Acid Study 1” and “Base Study 1” and 20mL of the buffer solution was transferred to each beaker with the use of a 25mL graduated cylinder a. A 10mL graduated cylinder was filled with a 0.10 M HCl b. 5mL of 0.10 M of HCl were added to the beaker labeled a “Acid Study 1” in a 1.0mL parts with a dropper and recorded the pH after each addition c. The dropper and the 10mL graduated cylinder were rinsed multiple times. d. Steps 4a and 4b were repeated with 0.10M NaOH instead of HCl and added to the beaker labeled as “Base Study 1”. 5. The solution was discarded in the waste, the graduated cylinder, beaker and droppers used in previous steps were rinsed and dried. The beakers were relabeled as “Acid Study 2” and “Base Study 2”. 6. The remaining 10mL of “Buffer Sample” into an empty 50mL graduated cylinder then filled to the top with distilled water. 7. A 100mL beaker was labeled as “Diluted Buffer Sample” then, transferred the solution from step 6 to it and measured the pH.

Part III: Comparison of Buffer and unbuffered solutions 8. A. 50mL beaker was labeled as “HCL unbuffered” and one drop of 0.10M HCl was added and exactly 20.0mL of distilled water a. The pH of the solution was measured b. 1.0mL of 0.10M NaOH to the solution and measured the pH

Calculations Buffer pH Study Buffer Sample solution initial pH: 4.80 pH after addition of 0.10M HCL Total volume added pH 1.00 mL 4.74 2.00 mL 4.68 3.00 mL 4.64 4.00 mL 4.48 5.00 mL 4.54

pH after addition of 0.10M NaOH Total volume added pH 1.00 mL 4.84 2.00 mL 4.91 3.00 mL 4.94 4.00 mL 5.00 5.00 mL 5.04

Calculated buffer capacity (moles NaOH):

Diluted Buffer Sample solution initial pH: 4.81 Calculated buffer capacity (moles NaOH): pH after addition of 0.10M HCL Total volume added pH 1.00 mL 4.46 2.00 mL 4.28 3.00 mL 3.81 4.00 mL 3.00 5.00 mL 2.44

pH after addition of 0.10M NaOH Total volume added pH 1.00 mL 5.07 2.00 mL 5.37 3.00 mL 5.86 4.00 mL 11.11 5.00 mL 11.72

Initial pH of unbuffered HCl: 3.87 pH after addition pf. 1.0mL NaOH: 11.60

pH of Buffer Solutions 14 12 10 pH B1 HCl added pH B2 NaOH added pH D1 HCl added pH D2 NaOH added

pH

8 6 4 2 0 0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

Volume of HCl and NaOH added, mL

Discussion: Buffer solutions are solutions with special properties that can resist specific changes to their pH after adding acids of based. How much acid or base can be added to the buffer solution is determine by its capacity. In the experiment we can appreciate the capacity of the buffer prepared during the solution. If we compare the buffer solution and the diluted buffer after adding HCl, we can see that the diluted solution does not have the same capacity as the buffer solution. On the diluted solution the pH was lowered than the buffer solution, the change on the pH was also faster after each addition. The pH of the diluted buffer solution after adding the 5mL of HCl decreased to 2.44; while the pH of the buffer solution was hardly changed, it was only lowered to pH 4.54 and the original pH of the buffer solution was 4.80. Comparing the buffer solution and diluted solution after adding NaOH we can see the same pattern of the pH changes as with HCl. The pH of the buffer solution was hardly changed, after adding the 5mL of NaOH we can see that pH increased to 5.04 which was not a substantial change from the original pH 4.81. In the other hand, the pH of the diluted buffer solution after adding NaOH increased a lot and rapidly. The pH of the diluted buffer solution increased to 11.72. The solution had a basic pH compared to the original pH that was acid.

If we compare the behavior of the pH of the buffer solution, diluted solution with the unbuffered solution we can see the drastic change of the pH within seconds even from very acetic after adding one drop of HCl and how fast it increased after adding 1.0mL of NaOH increasing to 11.60.

Er r o r s : Th es o ur c eo fe r r o rd ur i n gt h i se x pe r i me n tc ou l dh a v eb e e nn otu s i n gc l e a n e d a n ddr i e dl a bo r a t or yut e ns i l s . Al s o ,n o ta dd i n gt h ec o r r e c ta mou n to fs ol u t i on e a c ht i me . An dno ta l l o wi n gt h es ol u t i ont obemi x e df ul l ybe f or er e c o di n g t h ep H. Ca ut i o n: Du r i n gt h i se x pe r i me n ts t r o n ga c i d swe r eus e d ,wh i c ha r eh i g hl yc o r r o s i v e t h e r e f or e , r e q ui r et ob eha nd l ewi t he xt r e mec a ut i on .Pr e v e ntg e t t i n gs p l a s he d wi t ha n yoft h es ol ut i on s . Al s o , t h eus eo fs a f e t yg o g g l e sa ta l lt i me s .

Conclusion: In this experiment we were to prepare the buffer solution. The changes in pH were successfully compared the change on the pH after the addition of HCl and NaOH of the buffer solution, the diluted buffer solution and unbuffered solution. The buffer solution met the purpose of having a minor change after the 5mL of HCl and NaOH were added. While the diluted buffer solution had a more noticeable change on the pH then the original buffer solution. Lastly, the buffer functionality was compared to the unbuffered solution where with a small amount of the HCl and NaOH the change on pH was stunningly change.

REFERENCES 1. Brown, Theodore L.; LeMay, H. Eugene; Bursten, Bruce E.; Chemistry: The Central Science, 11th Edition, Prentice-Hall, 2008.

2. Rivera-Torres, Ivan. SCC202 Fundamentals of Chemistry Laboratory Manual II; Cengage Learning, 2009, pp 57 – 69....