Determining Concentration of a solution Lab

Determining the Concentration of a Solution: Beer’s Law

Purpose:
The purpose of the experiment is to determine the concentration and formula of an unknown cobalt nitrate solution by measuring absorbance.

Introduction:
A Colorimeter will be used to determine the concentration and formula of an unknown cobalt nitrate solution. The colorimeter sends blue light from the LED light source to pass through the solution and hit a photocell. A solution with a higher concentration will absorb more light and transmits less than s solution of lower concentration.
Five solutions with a known concentration of cobalt chloride hexahydrate will be used. Each solution will be put into a small cuvette which will ultimately be placed inside the colorimeter to find the amount of light that strikes the photocell; calculating the absorbance. When the absorbance to concentration information is graph it should be a direct relationship resulting in a linear relationship.
Three samples of unknown cobalt chloride hexahydrate will be obtained. The samples contain the same compound but different concentrations. By entering the absorbance on the relationship graph from part one, the concentration can be obtained.

Observations:
All solutions were a pinkish color liquid. As the concentration increased, the concentration increased as well.

Data:
Data Table 1: Standard Solutions- Co
Trial
Concentration (mg/mL)
Concentration, calc. (mol/L)
Absorbance
1
8
0.034
0.106
2
16
0.068
0.231
3
24
0.10
0.339
4
32
0.14
0.454
5
40
0.17
0.597

Data Table 2: Unknown Solutions-
Trial
Concentration (mg/mL)
Concentration, exp. (mol/L)
Absorbance
1
20
0.078
0.254
2
26
0.0879
0.276
3
32
0.088
0.30

Graph 1: Concentration and Absorbance Relationship of Standard Solutions

Graph 2: Concentration and Absorbance Relationship of Unknown Solutions

Calculations:
1. To start the experiment the given concentration of (mg/mL)