CHM110H5 Study Guide - Final Guide: Titration Curve, Ph Meter, Titration

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Experiment 3
Identification of an Unknown Acid
October 31, 2014
Purpose
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The purpose is to identify an unknown acid by using pH indicators and titrating it with a base to
obtain the Ka value using the equation:
Ka = [HO][A]/[HA]
The concentrations for this equation would be identified by pH titration and the resulting Ka
value would be compared to those of identified acids to see which acid the Ka value is the same
as. The acid could then be identified. A known acid, HCl, is also to be titrated with a strong base
to find the concentration of it at the equivalence point.
Experimental Method
The pH meter was placed in each of three buffer solutions with known pH values. In between
placing the meter in the solutions, the meter was rinsed with distilled water.
The unknown acid was placed in a beaker and titrated with sodium hydroxide. A magnetic
stirring bar kept the solution mixed. Moderate amounts of NaOH were titrated until a large
increase in pH occurred. After the large increase, smaller amounts were added until the pH
appeared more stable.
The same process was completed, but HCl was used instead of the unknown acid.
Some of the unknown acid was poured into three test tubes. Different indicators were then added
to each of them. The colours were compared to those of the test tubes on the racks and were put
in order of increasing acidity. The unknown acid was then identified by seeing which colours
were most similar, and matching it up with that unknown.
Results
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Figure 1.0: Titration curve for HCl
HCl + NaOH  HO + NaCl
1. CAVA = CBVB
CA(0.025L) = (0.1003mol/L)(0.0268L)
CA = 0.011 mol/L
Figure 2.0: Titration curve for unknown acid
Figure 3.0: Derivative of titration curve for unknown acid
2 . CAVA = CBVB
CA(0.025L)=(0.1003mol/L)(0.0289L)
CA=0.116mol/L
Concentration of unknown acid is 0.116mol/L
3.
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Document Summary

The purpose is to identify an unknown acid by using ph indicators and titrating it with a base to obtain the ka value using the equation: The concentrations for this equation would be identified by ph titration and the resulting ka value would be compared to those of identified acids to see which acid the ka value is the same as. A known acid, hcl, is also to be titrated with a strong base to find the concentration of it at the equivalence point. The ph meter was placed in each of three buffer solutions with known ph values. In between placing the meter in the solutions, the meter was rinsed with distilled water. The unknown acid was placed in a beaker and titrated with sodium hydroxide. A magnetic stirring bar kept the solution mixed. Moderate amounts of naoh were titrated until a large increase in ph occurred.

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