Analysis of Household Vinegar

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Analysis of Household Vinegar

Introduction to Chemistry Lab

 

Banerjee

 

 

Purpose:

The purpose of this lab is to determine the concentration of acetic acid in household vinegar. A sodium hydroxide solution will be prepared and used to titrate the vinegar.

 

Introduction to Volumetric Analysis:

1) A burette is an instrument used in a chemistry lab to precisely measure the amount of substance present in an unknown solution.

2) In an acid-base titration, a basic (or acidic) solution of unknown concentration is added to an acidic (or basic) solution with a known concentration. The pH is monitored, either through a pH probe or an appropriate indicator, to determine the end point.

3) The endpoint of a titration is the point where the indicator changes color.

4) The endpoint is commonly used to determine the equivalence point, the point where equivalent amounts of titrant and unknown are present.

 

Introduction to Concentration:

1) Concentration is the amount of solute present in a given amount of solvent or solution. Concentration can be expressed using different units.

2) mass percent = (mass of solute / mass of solution) x 100

3) molarity (M) = moles of solute / liters of solution

4) Stoichiometry can be applied to reactions involving solutions using molarity as a unit factor to convert between moles and volume.

 

Balanced Equation:

HC2H3O2 (aq) + NaOH (aq) H2O (l) + NaC2H3O2 (aq)

(d = 1.01 g/mL)

Safety:

1) Sodium hydroxide (NaOH) is caustic; wear gloves, safety goggles and protective clothing at all times.

 

 

Procedure:

Part 1: Preparation of 0.500 M NaOH

1) Obtain a 100.0 mL volumetric flask with a stopper.

2) Calculate the mass of NaOH necessary to prepare 100.0 mL of a 0.500M aqueous solution.

3) Obtain this quantity of NaOH, on a piece of weigh paper, on an analytical balance. Transfer the NaOH to the 100.0 mL volumetric flask

a. Record the exact mass in the data table attached.

4) Transfer the NaOH to the 100.0 mL volumetric flask

5) Add up to a few centimeters below the 100.0 mL mark with deionized water. Affix a stopper to the flask and mix until the NaOH is completely dissolved. Add water to flask, to bring the solution volume to 100.0 mL, if necessary.

6) Calculate the actual molarity of NaOH, using your measured quantity of NaOH.

 

Part 2: Titration to Determine the Concentration of Acetic Acid in Vinegar

1) Obtain three 250 mL Erlenmeyer flasks, a 100 mL beaker, a grease pencil, a 50 mL graduated cylinder, a buret, a buret clamp, a buret stand, a short stem funnel, 10 mL volumetric pipet, and a pipet pump.

2) Using a grease pencil, label the three flasks as “titration 1”, “titration 2”. Label the 100 mL beaker as “vinegar”.

3) Obtain 50 mL of vinegar in a 50 mL graduated cylinder. Transfer to the labeled 100 mL beaker.

4) Discard the water in the buret down the drain. Clamp the buret to the buret stand, using a buret clamp. Place an empty 100 mL beaker below the buret.

5) Ensure the stopcock is closed. Using a short stem funnel, add approximately 10 mL of your prepared NaOH solutoin to the buret.

6) Condition the buret by holding it horizontally and rotating to allow the NaOH to wet the inside of the glass completely. Discard the rinse into the sink.

7) Fill the buret with your NaOH solution and adjust the meniscus to zero.

a. Record the initial buret reading as 0.00 mL.

8) Transfer 10 mL of vinegar to each 250 mL flask, using a clean, 10 mL volumetric pipet.

9) Transfer 25 mL of deionized water to each 250 mL flask, using a 25 mL graduated cylinder.

10) Add 3-4 drops of phenolphthalein indicator to each titration flask.

11) Place the flask labeled “titration 1” under the tip of the buret.

12) While swirling the flask, slowly add the sodium hydroxide to the vinegar solution to a light pink endpoint.

a. The endpoint is reached when a faint pink color persists for at least 30 seconds, throughout the solution, after it has been swirled.

b. The pink will eventually fade, due to the absorption of carbon dioxide from the air and the slow reaction between the acid and base.

13) Once the endpoint has been reached, record the final level of NaOH solution in the buret.

14) Repeat steps 11-13 with titration flasks 2 and 3. Refill the buret with your NaOH solution, as needed.

15) Place all vinegar and sodium hydroxide solutions in the same waste beaker. Neutralize, if needed and discard in the sink.

16) Rinse the buret and glassware with water to remove all traces of NaOH. Refill the buret with deionized water.

 

Clean – Up:

1) Place all vinegar and sodium hydroxide solutions in the same waste beaker. Neutralize, if needed and discard in the sink.

2) Rinse the buret and glassware with water to remove all traces of NaOH. Refill the buret with deionized water.

 

 

 

 

 

 

 

 

 

 

 

Data Table:

Part 1: Preparation of 0.500 M NaOH

a) mass of NaOH

b) moles of NaOH

c) total volume in volumetric flask 100.0 mL

d) molarity of NaOH solution

 

Part 2: Concentration of Acetic Acid in Vinegar

titration 1 titration 2

a) volume of vinegar titrated 20.0 mL 20.0 mL

b) initial buret reading

c) final buret reading

d) volume of NaOH delivered

e) moles of NaOH delivered

f) moles of acetic acid

g) molarity of acetic acid

h) average molarity

i) mass of acetic acid per liter

j) mass percent of acetic acid

k) average mass percent

 

 

Discussion problem

1. A 10.0 mL sample of household ammonia is titrated with 18.15 mL of 0.300 M HCl to reach neutralization.

a. Calculate the molar concentration of ammonia in the solution.

 

 

 

 

b. Calculate the mass percent of ammonia in the solution. The density of the ammonia solution is 0.990 g/mL.

 

 

 

 

 

 

 

5

Introduction to Chemistry Lab

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