LAB#55 PERCENTAGE OF ACETIC ACID IN VINEGAR

Purpose:

Compare; To determine the percentage by mass of acetic acid in vinegar.

Introduction:

Acetic acid is produced by the bacterial oxidation of ethanol.
Vinegar is the resulting solution of acetic acid is called vinegar.

In this experiment, mass of vineger and concentration of sodium hydroxide solution are given. The sodium hydroxide will neutralize the acetic acid. Phenolpohthalein is added to indivate which the acetic acid has been completely neutralized by sodium hydroxide.

With knowledge of the concentration and the volume of the sodium hydroxide, you are able to know number of moles of sodium hydroxide used. Since acetic acid has one removable hydrogen atom per molecule, one mole of sodium hydroxide will neutralize one mole of acetic acid:
NaOH_(aq) + HC₂H₃O₂_(aq) → NaC₂H₃O_2(aq) + H₂O_(l)
And the number of moles of acetic acid present in the vinegar can be obtained and used to calculate the mass of acetic acid in the known mass of vinegar.

Apparatus and Materials:

■150mL beaker
■50mL buret
■buret clamp
■250mL beaker
■ring atand

■250mL Erlenmeyer flasks(2)
■50mL graduated cylinder
■vinegar
■sodium hydroxide (1.00mol/L)
■phenolphthalein solution

Procedure:

01. Label two Erlenmeyer flasks 1 and 2 for 1st and 2nd experiment.
02. Determine the mass of each flask.
03. Take 5mL of vinegar into a graduated cylinder.
04. Measure 20mL of vinegar into each flask.
05. Determine the total mass of each flask containing the vinegar.
06. Add one drop of phenolphthalein solution to each flask.
07. Fill the buret with NaOH so that the meniscus of the solution, and fasten the buret to a ring stand with a buret clamp.
08. Open the buret and drop some the sodium hydroxide solution until the solution turn the color.
09. From all infomation you got in this experiment, fill the data table.
10. Refill the buret and repeat the titration using the second flask.
11. Clearn up.

Data Table:

Measurements	#1	#2
Mass of flask and vinegar	143.37g	139.29g
Mass of empty flask	124.24g	120.67g
Volume of NaOH used	26.8mL	24.1mL

Observations:

Q1. What is the colour of phenolphthalein in vinegar?

- Pink

Q2. Calculate the moles of sodium hydroxide used in each titration.

- 26.8 x 0.001 = 0.0268 mole (#1)
- 24.1 x 0.001 = 0.0241 mole (#2)

Q3. How many moles of acetic acid were present in each sample of vinegar?

- 26.8/19.13 / 1000x19.13 = 0.00268 mole (#1)
- 24.1/18.62 /1000 x18.62 = 0.00241 mole (#2)

Q4. Calculate the mass of acetic acid in each sample of vinegar.

- 0.00268 x 1.01 = 0.0027068g (#1)
- 0.00241 x 1.01 = 0.0024341g (#2)

Q5. Determine the percentage of acetic acid in each sample of vinegar and compute the average.

- 0.00268 / 19.13 x 1000 x 100 = 14％ (#1)
- 0.00241 / 18.62 x 1000 x 100 = 12.9％ (#2)
- (14 + 12.9) /2 = 13.45％ (Average)

Q6. If 10.35g of vinegar neutralized 31.44 mL of 0.347 mol/L sodium hydroxide in a titration, what was the percentage by mass of acetic acid in the vinegar?

- 10.35 / 0.347x0.01035 x 100 = 30.87％

Q7. If 25.41 mol/L of acetic acid solution is neutralized by 35.47 mL of 0.255 mol/L sodium hydroxide, what is the concentration of the acetic acid?

- 35.47 x 0.255 / 25.4 = 0.36

Conclusion:

From the Question 5, the percentage by mass of acetic acid in vinegar is around 13.45％.

Conclusion Question:

Q8. What additional information would you need in order to use the data of this experiment to calculate the concentration of acetic acid in moles per litre?

- In order to find the concentration of acetic acid, you need to know the volume of the solution.

Q9. What additional information would you need in order to use the data od this experiment to calculate the percentage by volume of acetic acid in vinegar?

- You need to know the mass of the solution in order to calculate the percentage by volume of acetic acid in vinegar.