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Determine the Equilibrium Constant, Kc, for the Acid-Catalyzed Reaction

Essay by   •  March 10, 2011  •  Lab Report  •  574 Words (3 Pages)  •  1,470 Views

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Statement of Purpose:

The purpose of the lab is to determine the equilibrium constant, Kc, for the acid-catalyzed reaction between an unknown ester and water to produce an unknown alcohol and an unknown carboxylic acid. Through a combination of measurements and calculation it will be possible to determine the equilibrium concentrations of the reactants and products. We will be using Unknown Ester #2 with a density of 0.9003 and Molar Mass of 88.11 g/mol.

Summaries of Procedure:

1.Sign out an unknown ester sample from the stockroom. Record the unknown number in you lab notebook.

2.Determine the density of deionized water, and of the 3 M DCL solution. Also record the density and molar mass of the ester and alcohol.

3.Prepare the reaction mixtures as given in Table 2. Measure and record the volumes to 0.01 ml precision. Cap each bottle and shake vigorously. Store the bottle in your lab drawer until the mixtures com to chemical equilibrium.

4.Calculate the mass of sodium hydroxide needed to prepare 0.5 L of a 0.7 M NaOH solution. On a trip balance, quickly weigh out roughly this mass of NaOH pellets, and dissolve them in deionized water. Pour the solution into a polyethylene bottle and add water to bring the total volume of solution to about 500 mL. Cap the bottle tightly, to prevent atmospheric

CO2 from entering and reaction with the NaOH.

5.Calculate the mass of potassium hydrogen phthalate (KHP) needed to neutralize 35 mL of 0.7 M NaOH solution. On a digital single-pan balance, weight out approximately this mass of KHP into a 150-mL Erlenmeyer flask. Record the mass to the full available precision.

6.Dissolve the KHP in 50 mL of deionized water. Add 2 drops of phenolphthalein indicator and titrate your NaOH solution to a pale pink endpoint. Repeat the weighing and titration two more times, then calculate the average molarity of your sodium hydroxide solution. The solution is now standardized.

7.In the second week, titrate the reaction mixtures. Transfer the contents of each numbered bottle to an Erlenmeyer flask, rinsing any remaining solution into the flask with deionized water. Add2 drops of phenolphthalein indicator to the flask and titrate to a pale pink endpoint with the standardized NaOH solution prepared last week.

Data:

Table 2. Reaction mixtures

Bottle #

3 M HCl (mL)

H20 (mL0

Ester (mL)

Alcohol (mL)

1

5

5

0

0

2

5

0

5

0

3

5

1

4

0

4

5

3

2

0

5

5

2

2

1

Ester #2

Density = .9003 g/mL

Molar mass = 88.11

NaOH solution

500 mL

14g NaOH

Alcohol #2

Density = .7893 g/mL

Molar mass = 46.07 g/mol

Erlenmeyer Flask

5 g KHP

50 mL Deionized water

2 drops of phenolphthalein

Reaction Mixture weights in Grams

Container #

Weight of Container (g)

HCL (g)

H20 (g)

Ester (g)

Alcohol (g)

1

17.581

4.978

5.188

0

0

1A

17.069

4.979

5.188

0

0

2

5.23

0

4.502

0

3

5.23

.9973

3.601

0

4

5.23

2.992

1.801

0

5

5.23

1.995

1.801

.7893

Standardized: Amount of NaOH added to KHP(mL)

1st

2.50-13.80

2nd

3.00-15.12

3rd

2.50-16.35

Titration:

Bottle #

Amount

...

...

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