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BTEC Applied Science Unit 2 Assignment A - Colorimetry
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BTEC Applied Science Unit 2 Assignment A - Colorimetry. Pictures included. Referenced throughout. Awarded a DISTINCTION.
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Unit 2Assignment A
Diana Duka
Colorimetry
Aims
The objective of this experiment is to find out the relationship between concentration and the
absorbance of coloured solution - CuSO4, using a colorimeter, to produce a calibration
curve. During the experiment, I will make 4 different concentrations of the standard solution;
0.8, 0.6, 0.4 and 0.2. The different concentrations of solution will then be measured by a
colorimeter to determine the absorbance of the colour in the solution. The results will be
recorded then plotted into a graph to show the calibration curve .
Introduction
Colorimetry is used to determine the concentration of a coloured compound in a solution by
measuring the light absorption of a specific wavelength/ colour. White light is a mixture of
different frequencies and wavelengths of light. The colours that we see are electromagnetic
radiation. These electromagnetic radiations are labelled as the ‘electromagnetic spectrum’
as a collective, for short; the EM spectrum. Us humans can only see a small portion of the
EM spectrum, with wavelengths ranging from 380 nm and 760 nm, these are the colours we
can see in the rainbow and are considered as ‘visible light’. However, there are other
wavelengths with much longer wavelengths than 760 nm. Wavelengths that fall out of the
range of visible light are usually infrared and ultraviolet rays. Scientists use a diffraction
grating to separate the different wavelengths in order to see the different colours present in
white light (see picture below).
Moreover, there are two types of colorimeters; colour densitometers, which are used to
measure the density of the colours present and colour photometers that measure the colour
transmission and reflection.
Colour densitometers are usually used by printing professionals to measure the density or
the saturation of a colour/ colours. It can also be used in gene study and is used as a
molecular tool to measure the radioactivity of a radiolabeled DNA. They can also be used for
industrial radiography so that the x-rays produced are within the required range.
Last, there are a few factors which affect the absorption of coloured light; concentration of
the substance, concentration of particles within the solution and the purity level of a
substance. The colorimeter shines the light through the coloured solution which is then
absorbed/ reflected. The higher the concentration within the coloured solution, the higher the
absorption will be. Within this report, I will be evaluating the accuracy of the relationship of
absorption and concentration.
(1.)
, [Figure 1 showing the diffraction grating]
Solution - chemical mixture of a solute that is dissolved in a solvent
Mixture - combination of different substances
Diffraction grating - an optical component that diffracts white light into different colours of
light
Absorption - process of substances taken up, by another substance
Compound - another word for mixture, something composed of two or more substances
Uses of colorimetry
● Test for water quality by screening chemicals present in water; chlorine, fluoride and
iron
● Haemoglobin in blood
● Identify illegal substances
● Consistency of colours (in fabrics, paint etc.)
Calibration
It is important to calibrate the equipment before an experiment because this can alter the
results and during the process it can show any defects or faults in the equipment. Laboratory
apparatus can age, just like any other equipment. If the equipment is old, the results from the
experiment can be inaccurate, imprecise and unreliable, which makes it overall
unrepeatable.
Equipment needed to calibrate the digital scale
● Digital scale
● 100g masses
○ How to calibrate the digital scale
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