# Chemistry Titration Acid Base Lab

by qtpa2tea (student)

Acid-Base Titration Lab

By: Shawn Vickar

Question: What effect does an indicators pH range have on the end point of the titration of vinegar and 1.00 mol dm-3 of sodium hydroxide solution?

Equation: CH3COOH (aq) + NaOH (aq)  NaCH3COO (aq) + HOH (l)

Data Collection Table A: Table Representing the Initial Volume of NaOH in the Burette, the Final Volume of NaOH in the Burette and the Difference between Those Values for Specific Trials When Using Different Indicators. There were a minimum of three trials performed for this lab as there needed to be three of the same difference between the final and initial burette readings of the sodium hydroxide. This is due to the fact that a titration lab requires one to acquire three of the same values for this section to understand the exact amount of base required to reach the endpoint of the reaction.

Data Processing Table B: A Representation of the Volume of Sodium Hydroxide that was Required to Titrate 10ml of Vinegar, the Concentration of the Acetic Acid for the Specific Indicator Used, Concentration of Sodium Hydroxide, Percent Error and Percent Uncertainties.

Sample Calculation A: Calculation to Determine the Concentration of the Acetic Acid For the Different Indicators Used to Titrate the Sodium Hydroxide Solution.

Example Indicator: Bromocresol Green

NaOH Volume:  0.4ml

NaOH Concentration:  1.00mol/dm3

1. Convert Volume of the Sodium Hydroxide Solution from Milliliters to Liters

0.4 = 0.0004L

1000

1. Calculate the Moles of the Sodium Hydroxide Solution  Using the Values of its Volume and Concentration

n=C×V

n= (1.00mol/dm3) (0.0004L)

= 0.0004mol

1. Determine the Concentration of the Vinegar (Acetic Acid).

C = n

V

C = 0.0004mol = 0.04mol/L
0.01L

*From the equation, CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + HOH (l), the ratio of acetic acid and sodium hydroxide is 1:1. Therefore, they have equal amount of moles.

1. Calculate the Initial Concentration of Acetic Acid Before Diluted With Distilled Water

C1V1 = C2V2

C1= C2V2

V1

C1= (0.09mol/dm3)(0.1L)

(0.01L)

Concentration of Acetic Acid Before Dilution = 0.9mol/dm3

Sample Calculation B: Calculating Percent Uncertainty for the Volume of Sodium Hydroxide Needed for Different Indicators

Example: Bromocresol Green

=

×

=25.0%

Sample Calculation C: Calculating the Percent Error

Percent error

)×100

) ×100

=0.034%

Sample Calculation D: Propagating Uncertainty for the Volume of Sodium Hydroxide Required for Each Indicator

= (0.9±0.1) + (1.5±0.1) + (0.2±0.1) + (2.9±0.1) + (0.4±0.1)

= 5.9ml±0.1

Graph A: Titration curve of the Amount of Sodium Hydroxide Required to Reach the Endpoint for Different Indicators Tested

Graph B: Titrations curve of a strong base and weak acid. Approximately 9.2 is the pH of the equivalence point as seen in the graph.

Conclusion

This lab required one to determine the different volumes of sodium hydroxide base required to reach the end point of a titration with acetic acid as the analyte when using different indicators. The equation is as followed:

CH3COOH (aq) + NaOH (aq)  NaCH3COO (aq) + HOH (l)

It was determined that phenolphthalein was the best indicator for use in this lab. This is due to the fact that the vinegar that was used in class has an acetic acid concentration of 0.87 mol/L which is 5.0% acetic acid (Meheen, n.a). In the lab, phenolphthalein required 0.90 mol/L of ...