Determination of The Concentration of Acetic Acid in Vinegar

Table of Contents 1.1

Abstract...........................................................................................................................3

1.2

Introduction.....................................................................................................................4

1.3

Aims................................................................................................................................5

1.4

Theory.............................................................................................................................6

1.5

Apparatus........................................................................................................................7

1.6

Procedure.........................................................................................................................8

1.6.1

Standardization of Sodium Hydroxide Solution......................................................8

1.6.2

Molarity of acetic acid and percent of vinegar........................................................8

1.7

Results & Calculations..................................................................................................10

1.7.1

Standardization of Sodium Hydroxide Solution....................................................10

1.7.2

Standardization of Sodium Hydroxide Solution....................................................13

1.8

Discussion.....................................................................................................................16

1.9

Conclusion.....................................................................................................................17

2.0

Recommendation...........................................................................................................18

2.1

Reference.......................................................................................................................19

2.2

Appendix.......................................................................................................................20

1.1 Abstract The main purpose of this experiment is to determine the percent acetic acid contained in vinegar. As we know that acetic acid is a weak acid, we need to titrate it with strong base. The base chosen was Sodium Hydroxide (NaOH). The experiment was conducted by going through method of standardization of solution. A sample of vinegar was analysed by using titration method with Sodium Hydroxide (NaOH) and the graph pH versus Volume of Sodium Hydroxide titrated (mL) was plotted to determine the equivalence point of the titration. The mass percent of acetic acid obtained was 3.512%. Based on the theory, the percentage should be approximately 5-20%. Thus, there must be factors that affected the accuracy and precision of results. These error may be measurement error, eye of observer not perpendicular to the reading scale, losing amount of the solution when transferring to another container and others.

1.2 Introduction Acetic acid is an organic compound which is carboxylic acid. It is also considered as ethanoic acid. The chemical formula for acetic acid is

CH 3 COOH

.

Vinegar is one of the product that contains approximately 5-20% of acetic acid. There are ways to determine the amount of acetic acid in vinegar. In this experiment, we focused on titration method to determine the molarity and percent by mass of acetic acid in vinegar. Titration is the addition of a known concentration to an unknown until the solution reach neutralization. The solution will be titrated with a strong base which is Sodium Hydroxide (NaOH). Equivalence point is reached when the moles of titrant is equal to analyte. It can be obtained from the titration result. Ways to obtain the concentration of a solution is to determine their molarity and percent by mass. The molarity can be calculated by using equation below: Molarity (M) =

moles of solute liter o f solution

Percent by mass is also called as mass fraction. It is one of the way to represent the amount of concentration of an element in a mixture. It can be calculated by referring to the equation below:

Percent by mass (%) =

mass of so lute( grams) mass of solvent ( grams) ×100%

1.3 Aims The objective of this experiment is to find out the molarity and percent by mass of acetic acid in vinegar by titrating the solution with the standardized sodium hydroxide solution.

1.4 Theory A burette is used in titration process in order to determine molarity and percent by mass of acetic acid in vinegar solution. The burette must has the calibration unit of 0.1 mL to ease the process of determining equivalence point from graph pH versus volume of NaOH. Equivalence point is determined when the moles of base added in the solution is equal to moles of acid in the solution. Based on Equation (1.3-A) below, the number of mole of Sodium Hydroxide (NaOH) need to be 1 mole so that it can be neutralize with 1 mole of acetic acid. NaOH (aq )

+

CH 3 CO 2 H (aq )



NaCH 3 CO 2 (aq )

+

H 2 O ( l)

(Equation 1.3-A) When recording the pH value during titration process, there will be a sudden change in pH value. This indicates that the equivalence point has reached. pH is the +¿ ¿ measure of hydrogen ion concentration [ H 3 O . The equation of pH is as written in Equation (1.3-B).

pH

=

+¿ ¿ - log [ H 3 O (Equation 1.3-B)

The way to express the acidity or basicity of a solution is by determining the pH value of the solution. If the pH is less than 7, it is acidic. pH equals 7, it I neutral while more than 7 is basic. pH electrode is used to measure pH value of solution. The equivalence point of this titration can be determined by plotting a graph pH versus Volume of Sodium Hydroxide titrated to neutralize the acid.

1.5 Apparatus The apparatus used during this experiment to determine the amount of acetic acid in vinegar is:           

Vinegar 0.6 M of Sodium Hydroxide (NaOH) solution 10-mL Pipette 250 mL Beaker 250 mL Volumetric flask Burette stand Burette Funnel pH meter Stirrer Distilled water

1.6 Procedure 1.6.1

Standardization of Sodium Hydroxide Solution 1. 150 mL of Sodium Hydroxide solution (NaOH) solution with concentration about 0.6 M is prepared from NaOH solid. Use the beaker to produce the solution and record. Remember to recheck your calculation with the laboratory instruction. 2. Weigh approximately 1.500 grams of KHP and record the data. After that, add the KHP into a clean 250 mL volumetric flask with distilled water until calibrated mark and shake well. Transfer the solution into a 250 mL beaker. 3. Rinse burette with distilled water to make sure it is clean. Fill the burette with NaOH. Titrate the KHP solution with NaOH. The pH will be recorded with 1 mL addition of NaOH solution. 4. The NaOH solution is then standardized by repeating step1 to 3 for the second and third titration. 5. The volume of NaOH needed to neutralized the KHP solution can be diagnose by plotting a graph of pH vs volume of NaOH needed to neutralize the KHP solution (mL). 6. The molarity of NaOH and average molarity of NaOH solution for titration 1 and 2 is the calculated because it is needed for the second part of experiment.

1.6.2

Molarity of acetic acid and percent of vinegar 1. Measure 10.00 mL of vinegar and add them into a 250 mL clean beaker and add 75-100 mL of distilled water. Stir the solution. 2. Add more NaOH solution into the burette used in the previous experiment to the 0.00 mL line. Titrate the solution with NaOH. 1ml of NaOH is added in the solution. Record the pH of the solution, remember to rinse the electrode every time the pH of the solution is measured. 3. Step 1 and 2 is repeated for titration result 1 and 2.

4. To determine the volume of NaOH needed to neutralized the vinegar solution, graph pH versus volume of NaOH added is plotted. 5. The molarity of acetic acid, average molarity, percent by mass of acetic acid in titration 1 and 2 is calculated. We also needed to calculate the percent by mass of acetic acid in vinegar.

1.7 Results & Calculations 1.7.1

Standardization of Sodium Hydroxide Solution A. Standardization of Sodium Hydroxide Solution Titration 1

Titration 2

Titration 3

Mass of KHP (g)

1.507

1.506

1.501

Volume of NaOH to neutralize the KHP solution

12.10

12.15

14.10

B. Calculation of molarity of Sodium Hydroxide (NaOH) for each titration 1, 2,and 3. a) Titration 1  Moles of KHP used in tritration 1. 1.507 g = 

KHC 8 H 4 O4

0.00738 mol

×

KHC 8 H 4 O4

Moles of Sodium Hydroxide (NaOH) required neutralizing the moles of KHP. 0.00738 mol KHP



1mol KHC 8 H 4 O4 204.2 g KHC8 H 4 O4

×

1 mol NaOH 1 mol KHP

= 0.00738 mol NaOH Molarity of Sodium Hydroxide (NaOH) solution. 12.10 mL NaOH

×

1L 1000 mL

= 0.0121 L NaOH Molarity =

0.00736 mol NaOH 0.0121 L NaOH

= 0.60826 M NaOH b) Titration 2  Moles of KHP used in tritration 1. 1.506 g = 

KHC 8 H 4 O4

0.00738 mol

1mol KHC 8 H 4 O4 204.2 g KHC8 H 4 O4

×

KHC 8 H 4 O4

Moles of Sodium Hydroxide (NaOH) required neutralizing the moles of KHP. 0.00738 mol KHP



×

1 mol NaOH 1 mol KHP

= 0.00738 mol NaOH Molarity of Sodium Hydroxide (NaOH) solution. 12.15 mL NaOH

1L 1000 mL

×

= 0.01215

L NaOH

Molarity =

0.00738mol NaOH 0.01215 L NaOH = 0.60741

M NaOH

c) Titration 3  Moles of KHP used in tritration 1. 1.501 g = 

KHC 8 H 4 O4

0.00735 mol

1mol KHC 8 H 4 O4 204.2 g KHC8 H 4 O4

KHC 8 H 4 O4

Moles of Sodium Hydroxide (NaOH) required neutralizing the moles of KHP. 0.00735 mol KHP



×

×

1 mol NaOH 1 mol KHP

= 0.00735 mol NaOH Molarity of Sodium Hydroxide (NaOH) solution.

14.10 mL NaOH

×

1L 1000 mL

= 0.0141 L NaOH Molarity =

0,00735mol NaOH 0.0141 L NaOH = 0.52128 M NaOH

C. Calculation of the average molarity of Sodium Hydroxide (NaOH) for each titration 1,2 and 3.

Molarity =

=

0.60826 M +0.60741 M + 0.52128 3 1.73695 M 3

= 0.57898 M

NaOH

1.7.2

Standardization of Sodium Hydroxide Solution

A. Neutralization of Vinegar Solution

Volume of NaOH required to neutralize Vinegar (mL)

Titration 1

Titration 2

10.00

10.20

B. The molarity of acetic acid in vinegar for titration 1 and titration 2. a) Titration 1  Moles of Sodium Hydroxide (NaOH) that reacted in titration 1. 10.00 mL

1L

× 1000 mL

= 0.01000 L NaOH 0.01000 L NaOH ×

0.57898mol NaOH 1 L NaOH solution

= 0.005789 mol NaOH  Moles of CH 3 COOH neutralized by the moles of NaOH. 0.005789 mol NaOH × = 0.005789 mol

1 mol CH 3 COOH 1 mol NaOH

CH 3 COOH

 Molarity of CH 3 COOH ) solution. 10 mL

CH 3 COOH

×

1L 1000 mL

= 0.010 L Molarity =

=

CH 3 COOH mol CH 3 COOH Lof solution 0.005789mol CH 3 COOH 0.01 L solution

= 0.57898

M

CH 3 COOH

b) Titration 2  Moles of Sodium Hydroxide (NaOH) that reacted in titration 2. 10.20 mL

1L

× 1000 mL

= 0.01020 L NaOH 0.01020 L NaOH ×

0.57898mol NaOH 1 L NaOH solution

= 0.00591 mol NaOH  Moles of CH 3 COOH neutralized by the moles of NaOH. 0.00591 mol NaOH × = 0.00591 mol

1 mol CH 3 COOH 1 mol NaOH

CH 3 COOH

 Molarity of CH 3 COOH ) solution. 10 mL

CH 3 COOH

= 0.010 L Molarity =

CH 3 COOH mol CH 3 COOH Lof solution

×

1L 1000 mL

0.00591mol CH 3 COOH 0.01 L solution

=

CH 3 COOH

= 0.59056 M

C. The average molarity of acetic acid for titration 1 and 2. 0.57898 M +0.59056 M 2

Molarity =

= 0.58477 M

CH 3 COOH

D. Percent by mass of acetic acid in vinegar for titration 1 and 2.  Mass of acetic acid in the solution.

10 mL

CH 3 COOH CH 3 COOH

= 0.010 L 0.010

×

solution

CH 3 COOH

L

1L 1000 mL

0.58477 M CH 3 COOH 1 L solution

×

60.06 g CH 3 COOH 1 mol CH 3 COOH

= 0.35121 g

CH 3 COOH

 Mass of acetic acid solution.

10 mL

CH 3 COOH

= 10.00 g

solution

CH 3 COOH

×

1 g CH 3 COOH solution 1 mL CH 3 COOH solution

solution

 Percent by mass of acetic acid in the solution.

×

Percent mass

CH 3 COOH

=

=

g CH 3 COOH g CH 3 COOH solution 0.35121 g CH 3 COOH 10.00 g CH 3 COOH

= 3.512 %

CH 3 COOH

×100

1.8 Discussion During the lab session in this experiment, the main purpose is to determine the percent mass of acetic acid in vinegar. Therefore, one of the way to obtain this result is by titrating the Sodium Hydroxide (NaOH) with acetic acid. Potassium Hydrogen Phthalate (KHP) was titrated with 20.0 mL of Sodium Hydroxide (NaOH) Solution. The titration process was repeated twice so that the average molarity and reading of Sodium Hydroxide (NaOH) solution can be obtained. The pH value versus Volume of NaOH to neutralize KHP solution table and graph is then plotted to determine the equivalence point. Table and graphs of titration 1, 2 and 3 can be referred at Table 2.2A and Figure 2.2A, 2.2B, 2.2C in Appendix. The equivalence point is then determined. Thus, the average molarity of NaOH after going through standardization was 0.57898 M. In part B of experiment, Vinegar then was titrated with Sodium Hydroxide solution. There were two trials. The procedure is same as part A. Table and graphs of titration 1 and 2 can be referred at Table 2.2B and Figure 2.2D, 2.2E in Appendix. In trial 1, molarity of acetic acid was 0.57898 M. While in the second titration, the molarity of acetic acid was 0.59056M. The average molarity of acetic acid was then calculated which result to 0.58477 M of acetic acid. Lastly, the percent by mass if acetic acid was 3.512 %.

1.9 Conclusion Based on the experiment conducted, the vinegar and KHP was analysed by titration method with 0.6 M of Sodium Hydroxide (NaOH) solution. Then, a graph of pH versus Volume of Sodium Hydroxide (NaOH) titrated was plotted to get the equivalence point for the calculations. The mass percent of acetic acid in vinegar solution is 3.50 % which gives a big difference compared to the sample calculation in lab manual which is 1.96%. We can conclude that it has a huge difference due to some errors during the experiment. For example, the observer may jotted down the wrong pH value due to the lack of knowledge in using a pH meter, eyes not perpendicular to the scale of measuring tool and others.

2.0 Recommendation After the experiment was done, our lab group members have compared our results with the other group. The results have a slight difference compared to the other groups. This may be caused by errors during the experiment was done. First and foremost, the error affecting the result of experiment might be because of the misreading the volume. Observer can misread the volume during titration by looking the scale from the wrong angle. The Sodium Hydroxide solution will form a concave curve and observer should look at the bottom curve to measure the volume. Therefore, observer should make sure eyes are perpendicular to the scale. Then, another error that might affect the value is by using the equipment incorrectly. Air bubbles in burette can affect the flow of titrant due to error when filling the solution. Using the pH meter incorrectly and using electrode without rinsing with distilled water can also affect the result of experiment. End point error is also one of the reason affect the result of experiment. During titration, there will be a point where the reaction between two solutions stopped. Observer may look colour of indicator differently. Too much titrant is caused by change of colour of indicator.

2.1 Reference 1.

Writer, L. G. (n.d.). Errors in Titration Experiments. Retrieved March 31, 2017, from http://sciencing.com/errors-titration-experiments-8557973.html

2.

Determination of Acetic Acid In Vinegar Lab Explained. (n.d.). Retrieved March 31, 2017, from https://schoolworkhelper.net/determination-of-aceticacid-in-vinegar-lab-explained/

3.

Lab Investigation 2 - How Much Acetic Acid is in Vinegar? (n.d.). Retrieved March 31, 2017, from http://www.webassign.net/question_assets/tccgenchem2l1/lab_2/manual.ht ml

4.

General Chemistry Labs. (n.d.). Retrieved March 31, 2017, from http://www.odinity.com/acetic-acid-content-vinegar/

5.

Measuring the Amount of Acetic Acid In Vinegar | Chemistry Science Fair Project. (n.d.). Retrieved March 31, 2017, from http://www.seminarsonly.com/Engineering-Projects/Chemistry/Measuringthe-Amount-of-Acetic-Acid.php

6.

2.2 Appendix pH of the solution Volume of Sodium Hydroxide to Titration Titration Titration 1 2 3 neutralize the KHP solution (mL) 0 4.16 4.41 4.37 2 4.55 4.68 4.56 4 4.90 4.97 4.87 6 5.38 5.39 5.18 8 5.50 5.51 5.47 10 5.85 5.88 5.82 12 5.92 5.90 6.73 14 11.33 11.31 11.28 16 11.74 11.62 11.57 18 11.81 11.73 11.73 20 11.99 11.84 11.88 Table 2.2A pH vs Volume of NaOH

KHP Titrated with NaOH 14 12 10 8 pH

Titration 1

6 4 2 0 0

2

4

6

8

10

12

14

16

18

Volume of Sodium Hydrox ide NaOH (mL)

20

Figure 2.2A graph pH vs Volume of Sodium Hydroxide in Titration 1

KHP Titrated with NaOH 14 12 10 8 pH

Titration 2

6 4 2 0 0

2

4

6

8

10

12

14

16

18

20

Volume of Sodium Hydroxide NaOH (mL)

Figure 2.2A graph pH vs Volume of Sodium Hydroxide in Titration 2

KHP Titrated with NaOH 14 12 10 8 pH

Titration 3

6 4 2 0 2

4

6

8

10

12

14

16

18

20

Volume of Sodium Hydrox ide NaOH (mL)

Figure 2.2A graph pH vs Volume of Sodium Hydroxide in Titration 3

pH of solution Volume of NaOH required to neutralize vinegar 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Titration 1

Titration 2

2.85 3.55 3.89 4.15 4.36 4.55 4.73 4.93 5.09 5.34 5.81 10.89 11.48 11.62 11.76 11.78 11.86 11.94 12.01

3.03 3.68 4.04 4.20 4.44 4.59 4.77 4.93 5.18 5.47 6.24 11.01 11.42 11.60 11.76 11.80 11.93 11.97 12.09

Table 2.2A pH vs Volume of NaOH

Vinegar Titrated with Sodium Hydroxide 14 12 10 8 pH

Titration 1

6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Volume of Sodium Hydroxide NaOH (mL)

Figure 2.2D graph pH vs Volume of Sodium Hydroxide in Titration 1

Vinegar Titrated with Sodium Hydroxide 14 12 10 8 pH

Titration 2

6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Volume of Sodium Hydrox ide NaOH (mL)

Figure 2.2E

graph pH vs Volume of Sodium Hydroxide in Titration 2

-