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Lecture 2

CHM110H5 Lecture Notes - Lecture 2: George Li, Lab Report, Malachite


Department
Chemistry
Course Code
CHM110H5
Professor
Judith C Poe
Lecture
2

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Experiment # 3
Identification of An Unknown Acid By pH Titration
Student Name: Samar Ashraf
Student Number: 1002302322
Section Number: 105
Date the experiment was performed: October 19th 2015
Date the lab report was submitted: October 26th 2015
Submitted to George Li
Pre-lab Questions /20
Pre-lab quiz /5
Purpose /5
Experimental Method /10
Results and Calculations /20
Discussion /10
Summary /5
References /5
Experimental Technique /10
Report Presentation /10

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Purpose: The purpose of this lab was to identify an unknown sample of an acid by
experimentally determining the KA of the reaction by using pH meter titration. The acid was to
be identified as either acetic acid or a chloro derivative (mono, di, tri) of acetic acid.
Experimental method: The lab was started by calibrating the pH meter by using three buffer
solutions, pH 4, pH 7, and pH 10. The unknown acid was obtained and using a volumetric pipette
the acid was transferred into the 100mL beaker and titrated with the NaOH. A magnetic stirring
bar was used to keep the solution thoroughly mixed and the pH electrodes were inserted into the
beaker and made sure that it the magnetic stirring bar was not close to the electrodes. The first
3mL was titrated in about 0.25mL increments and then it increased to 1mL until the ph started to
rise and then the increments were reduced to single drops. In this experiment the titration was not
continued until 45mL. The procedure was repeated for HCl. The qualitative identification of the
unknown acid was done by using three indicators, thymol blue, malachite green and crystal
violet. The unknown acid was added to 3 test tubes and 5 drops of each indicator was added to
the test tube. The observation were recorded and according to the acidity of the tubes the
unknown acid was identified.
Calculations: Quantitative Identification
-2 3 8 13 18 23 28
0
2
4
6
8
10
12
Titration Curve for 25mL HCl
Amount of NaOH (mL) added to mixture
pH
Figure 1. The volume of base added against pH of solution for titration of 25mL of HCl of
unknown concentration with 26.25mL of 0.1002M of NaOH.
Volume of base added at equivalence point,
23.0mL + 26.25mL/2 = 24.625 mL
At equivalence point,
CAVA=CBVB
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