The assignment demonstrated exceptional understanding and application of colorimetric techniques. The student accurately determined the concentration of an unknown copper(II) sulfate solution by creating a precise calibration curve using a series of standard solutions. They effectively applied the ...
Practical: Colourimetry, finding the concentration of copper sulphate
Colourimetry can be referred to as colour science and is a technique in which shows how
much of a coloured compound is present. The colourimetry technique consists of creating differing
dilutions of a chemical to find a solutions concentration.
This is essential in fields such as photography and medical research where colourimetry is
used to better understand DNA synthesis.
By following this colourimetry practical, we can find the concentration of a solution of copper
sulphate with an unknown concentration using a colourimeter.
Calibration of colourimeter
To calibrate the colourimeter, it must measure absorbance at zero concentration to gain a zero
mark. This is done by using the colourimeter to measure the absorbance of distilled water:
1. Using a cuvette, distilled water was placed into the colourimeter with the frosted side facing
away from the light source.
2. Pressing onto the R button on the colourimeter, an absorbance of 0.00 was recorded as the
zero absorbance with zero concentration.
The colourimeter needs to be calibrated with distilled water before the practical as it shows the
colourimeter works correctly. In addition, the reading of 0.00 absorbance and a concentration of
0.00mol/dm3 is the 0 mark of the graph that will be constructed.
Method to find the concentration of the unknown CuSO 4:
To find the concentration of the unknown copper sulphate solution, the absorbance of other
known concentrations of copper sulphate solutions must be found first. With these different
absorbances and concentrations, a graph can be constructed to then find the concentration of the
unknown CuSO4 solution. A series of concentrations of 0.20mol/dm 3, 0.40 mol/dm3, 0.60 mol/dm3,
0.80 mol/dm3 and 1.00 mol/dm3 with equal intervals are the known concentrations where the
absorbances will be found to construct the graph.
Apparatus and material:
Test tubes (6x)
Test tube rack
Wash bottle with distilled water
10ml measuring cylinder
Copper sulphate
Cuvettes
1. The first sample of CuSO4 made had a concentration of 0.20mol/dm3
2. 2ml of copper sulphate was measured using a 10ml measuring cylinder
2.1. This was done at eyelevel to ensure the bottom of the meniscus was sitting on the 20ml line
of the measuring cylinder.
2.2. The measuring of 4ml of CuSO4 was done at eyelevel to ensure the meniscus was sitting on
to the 4ml line.
3. After 2ml of copper sulphate had been measured, the measuring cylinder was filled to the 10ml
line with distilled water from the wash bottle.
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