Chem 105A Lab Exam, Experiment 4 - Titrations (Volumetric Analysis)

What was the ultimate goal of this experiment?

Determine the acetic acid content in vinegar

What is an acid-base titration an example of?

Volumetric analysis

What is an analyte?

The substance being analyzed

What is the titrant?

Reagent solution delivered by a buret

How do we determine the concentration of an analyte?

Based off the amount of titrant required to reach the endpoint of the titration

What is the endpoint signaled by?

A change in the color of the indicator

What was the analyte in our experiment?

Acetic Acid

What was the titrant in our experiment?

sodium hydroxide

What was the mole ratio between acetic acid and sodium hydroxide?

1:1

Moles NaOH used = moles of acetic acid

What were the products of the reaction between acetic acid and NaOH?

sodium acetate and water

How did we determine the molarity of acetic acid in vinegar?

By finding the volume of sodium hydroxide used to reach the endpoint

What was the concentration of the NaOH stock solution? What did we dilute it to?

5M --> 0.5 M

What is a standard solution?

A solution that has a concentration which has been determined accurately and precisely

What must we use to standardize an unknown solution?

Primary Standard

What is a primary standard?

A substance that is stable, known to be pure, soluble, has a high molecular weight, and must not be hygroscopic

What did we use to determine the concentration of NaOH?

KHP (primary standard)

What is NaOH known as once its concentration has been determined?

Secondary standard

What is the mole ratio between KHP and NaOH?

1:1

How do we find the mass of KHP that will react with 10.32 mL of 0.509 M NaOH?

1. 10.32 mL --> L

2. L --> Moles NaOH

3. Moles NaOH --> Moles KHP

4. Moles KHP --> g KHP

What is the equivalence point?

The point at which the neutralization reaction is complete

Moles H+ = moles OH-

What is used to give a visual indication of the endpoint?

A dye

What is a dye made of?

Weak acid

What does the dye do in solution? What does this depend on?

Dissociates in solution depending on the acidity of the solution

Why must we choose a dye appropriate for the pH of the solution?

To ensure that the endpoint of the titration is equal to the equivalence point of the titration

What indicator did we use in the experiment?

Phenolphthalein

Can you titrate a solution of unknown concentration with another solution of unknown concentration and get a meaningful answer?

No, cannot use M1V1 = M2V2 with two unknown concentrations

What were the calculations in determining the concentration of NaOH?

1. g KHP --> moles KHP

2. Moles KHP --> moles NaOH

3. Moles NaOH --> molarity NaOH

4. use average molarity for NaOH

How did we calculate error in this lab?

Standard deviation and percent standard deviation

Is it important to know the mass of KHP used at the beginning of part one and the volume of acetic acid at the beginning of part two?

YES

What did we do the KHP powder in the flask at the beginning of the experiment?

Dissolved it in water

What should we do to the burets before using them?

Clean with water and then NaOH

What volume of vinegar did we use for the beginning of each trial in part 2?

10.0 mL using a volumetric flask

What should we know about the chemicals in this experiment?

NaOH hazardous to health

Phenolphthalein is flammable and health hazardous

Acetic acid is flammable and health hazardous

What data did we need to collect in this trial?

1. KHP/vinegar used

2. NaOH initial volume

3.NaOH final volume

4. NaOH volume

What were the steps of calculations in part 2?

1. Molarity NaOH --> moles NaOH

2. Moles NaOH --> moles acetic acid

3. Moles acetic acid --> g

How did we calculate the mass % acetic acid?

(Mass Acetic acid) / (mass vinegar) x 100%

How did we determine the mass of vinegar?

Multiple 10.0 ml by the density of vinegar (1.05 g/ml)

What was the average final mass percent acetic acid for my trial?

4.87%

How did we calculate error in this experiment?

standard deviation and percent standard deviation

How do we find the molarity of acetic acid that is 96.72% acetic acid by mass? (Density = 1.05 g/ml)

1. find mass acetic acid

2. (mass)/(g/mol) = moles acetic acid

3. Moles acetic acid/ 1 L = M

What did NaOH serve as in part 2 of the experiment?

Base

Titrant

Primary Standard

Will the calculated mass be different if you add 10 drops of dye instead of 2?

No, it is not part of the reaction