Colorimetry
Colorimetry
Introduction
Absorption Spectroscopic methods of analysis rank among the most widespread and powerful tools for quantitative analysis. The use of a spectrophotometer to determine the extent of absorption of various wavelengths of visible light by a given solution is commonly known as colorimetry. This method is used to determine concentrations of various chemicals which can give colours either directly or after addition of some other chemicals.
As stated by the Beer-Lambert Law - The amount of light radiation absorbed by a compound is directly related to the concentration of the compound.
Equipment
Copper Sulphate 1M solution
Sulphuric Acid 0.5 M solution
Volumetric Flasks 100 ml, 50 ml,
20ml
Pipettes 25 ml, 10 ml
Spectrophotometer
Safety Equipment
Enclosed footwear
Laboratory coat
Safety glasses
Rubber gloves
Method
1. Prepare 100ml of 0.250 M solution of CuSO 4 in 0.5 M H2 SO4 from 1 M CuSO 4 in 0.5 M
H2 SO4 solution provided. It is Standard 1 (Std 1). Ensure that the contents are thoroughly mixed. 2. Using Standard 1 solution make up 50ml 0.125 M of solution of CuSO 4 in 0.5 M H2 SO4 . It is Standard 2 (Std 2). Ensure that the contents are thoroughly mixed.
3. Using Standard 2 solution make up 20ml of solution of 0.0625 of CuSO 4 in 0.5 M H2 SO4 .
It is Standard 3 (Std 3). Ensure that the contents are thoroughly mixed.
4. Set the wavelength on the spectrophotometer at the absorption peak for blue solution (620 nm). Using tube No 1. (i.e. ”zero” or “reagent blank”) zero (or standardize) the instrument, and then record the absorbance of each solution.
5. Using the spectrometer (wavelength 620 nm) analyse blank, standard solutions and unknown concentration CuSO 4 solution. Record absorption of each solution. Note: The unit of wavelength (λ) is nm.
6. You are also provided with a sample of CuSO 4 at an unknown concentration. Record the absorption of this unknown solution.
Results
Test Tube
1
2
3
4
5
Introduction
Absorption Spectroscopic methods of analysis rank among the most widespread and powerful tools for quantitative analysis. The use of a spectrophotometer to determine the extent of absorption of various wavelengths of visible light by a given solution is commonly known as colorimetry. This method is used to determine concentrations of various chemicals which can give colours either directly or after addition of some other chemicals.
As stated by the Beer-Lambert Law - The amount of light radiation absorbed by a compound is directly related to the concentration of the compound.
Equipment
Copper Sulphate 1M solution
Sulphuric Acid 0.5 M solution
Volumetric Flasks 100 ml, 50 ml,
20ml
Pipettes 25 ml, 10 ml
Spectrophotometer
Safety Equipment
Enclosed footwear
Laboratory coat
Safety glasses
Rubber gloves
Method
1. Prepare 100ml of 0.250 M solution of CuSO 4 in 0.5 M H2 SO4 from 1 M CuSO 4 in 0.5 M
H2 SO4 solution provided. It is Standard 1 (Std 1). Ensure that the contents are thoroughly mixed. 2. Using Standard 1 solution make up 50ml 0.125 M of solution of CuSO 4 in 0.5 M H2 SO4 . It is Standard 2 (Std 2). Ensure that the contents are thoroughly mixed.
3. Using Standard 2 solution make up 20ml of solution of 0.0625 of CuSO 4 in 0.5 M H2 SO4 .
It is Standard 3 (Std 3). Ensure that the contents are thoroughly mixed.
4. Set the wavelength on the spectrophotometer at the absorption peak for blue solution (620 nm). Using tube No 1. (i.e. ”zero” or “reagent blank”) zero (or standardize) the instrument, and then record the absorbance of each solution.
5. Using the spectrometer (wavelength 620 nm) analyse blank, standard solutions and unknown concentration CuSO 4 solution. Record absorption of each solution. Note: The unit of wavelength (λ) is nm.
6. You are also provided with a sample of CuSO 4 at an unknown concentration. Record the absorption of this unknown solution.
Results
Test Tube
1
2
3
4
5
References: Various chemistry notes Chemistry – Human Activity Chemical Reactivity, authors – Mahaffy, Bucat, Tasker, Kotz, Treichel, Weaver, Mcmurray