CHEM 1AL Lecture Notes - Lecture 6: Titration Curve, Ph Meter, Potassium Bisulfate

291 views9 pages

fuchsiaporcupine53

26 Mar 2016

School

Department

Course

Professor

For unlimited access to Class Notes, a Class+ subscription is required.

Document Summary

Acid-base reactions: identification of an unknown weak acid. A ph indicator is itself a weak acid or base that changes color abruptly over a narrow ph range-typically over 2 ph units. One chooses an indicator that will change color near the expected equivalence point in a titration. The use of a ph meter for the titration of weak acids provides much more information than can be obtained by titration using an acid-base indicator. The ph meter permits a more accurate location of the equivalence point than does an indicator, and from the data it is possible to determine the acid dissociation constant (ka) reasonably accurately. The purpose of this experiment is to provide first-hand experience with the interpretation of data from a weak acid-strong base titration curve. The ph meter measures the voltage produced between a glass electrode and a stable reference electrode when they are both placed in solution.

Related Questions

Just final answers

	Trial 1	Trial 2
Volume of Unknown Weak Acid	4 mL	4 mL
Total Number of Drops Required to Reach Equivalence Point	5	5
Average Number of Drops	5

Drops NaOH Added	pH Value Trial 1	pH Value Trial 2	pH Value (Average)
Half-Equivalent Point = (46 Drops)	2.5	2.5	2.5
Equivalent Point = (93 Drops)	5	5	5
0	3.5	3.5	3.5
10	4.5	4.5	4.5
20	5.5	5.5	5.5
30	7.0	7.0	7.0
40	8.0	8.0	8.0
50	10.0	10.0	10.0
60	10.0	10.0	10.0
70	10.0	10.0	10.0
80	10.0	10.0	10.0
90	10.0	10.0	10.0
100	10.0	10.0	10.0
110	10.0	10.0	10.0
120	10.0	10.0	10.0

pK_a of Unknown Weak Acid:	2.5
K_a of Unknown Weak Acid:	3.16 x 10 ^-3
Unknown Weak Acid Identity:	Citric Acid
% Error pK_a:	10.39%
% Error K_a:	4.9%

A. pH indicator strips work by changing color in the presence of solutions with varied pH values. Thinking about your procedure steps and results in Part 1, why do you think the pH of the unknown weak acid was not determined with pH indicator strips until Part 2.

B. Discuss possible causes of error in the experimental procedure. Why do you think there was a percent of error in the pK_a and K_a values of the unknown weak acid, in comparison to the values presented in Table 2?

C. Do you think using a pH meter instead of pH indicator strips would have created a larger or smaller percent error? Explain your answer.

D. Why was phenolphthalein a good indicator to use for determining the equivalence point between the unknown weak acid and strong base?

CHEM 1AL Lecture Notes - Lecture 6: Titration Curve, Ph Meter, Potassium Bisulfate

Document Summary

Get access

Related textbook solutions

Chemistry: Structure and Properties

Basic Chemistry

Principles of Chemistry Molecular Approach

Chemistry: Structure and Properties

Principles of Chemistry Molecular Approach

Chemistry: A Molecular Approach

Chemistry: A Molecular Approach

Principles of Chemistry: A Molecular Approach

Chemistry: The Central Science

Related Documents

CHEM 1AL Lecture Notes - Lecture 4: Hydrochloric Acid, Acid Strength, Weak Base

CHEM 1AL Lecture Notes - Lecture 4: Complementary Colors, Sulfide, Drug Design

CHM135H1 Lecture Notes - Lecture 23: Bromothymol Blue, Titration Curve, Equivalence Point

Related Questions