Unit 1 assignment 6
Laboratory report
Investigation into the concentration of red diesel
Aim - carry out experiments to:
● To find out the correct wavelength filter to use with a red diesel solution
● Prepare a standard curve
● Determine the concentration of red diesel in different samples
Abstract
The concentration of dye in the forensic samples A and B was measured using the method
colorimetry to determine absorbance wavelengths. At full strength the dye in red diesel is 10
mg/cm3. The concentration of dye of the sample A was 7.8 mg/cm3 and this shows that the
solution was watered down. The concentration of dye of the sample B was 1.8 mg/cm3 and this
shows that the solution was also watered down.
Introduction
This practical uses the Beer-Lambert law which states that when light passes through a
coloured solution, some of the light will be absorbed. The amount of light absorbed is dependent
on the concentration of the solution, therefore the darker the solution, the higher the
concentration and the more light that will be absorbed. For coloured solutions, you need to use
a specific color or wavelength of filter to give the optimum absorbance.
For example, with a green filter - white light will be directed through a filter and green light will
be transmitted through the filter which makes the filter green. Other wavelengths will be
absorbed into the solution. In this case, the beer-lambert law can be used to find out whether
the red diesel has been watered down.
Equipment
● A standard solution of dye at 16mg cm-3
● A colorimeter
● Appropriate filter
● Cuvettes
● Cuvette rack
● Glass pipettes
, Unit 1 assignment 6
● 6 Test tubes
● Test tube rack
● 2 forensic samples
● Marker pen
Method
Preparation of solutions for the standard curve
1. A variety of solutions of different concentrations of red dye were prepared to cover a
concentration range of 0-16mg/cm3. These were prepared using a dye at 16mg/cm3 and
water shown in the table below:
Tube Concentration Volume of red Volume of Total volume
of red dye dye required at water required
(mg/cm3) 16mg/cm3 (cm3)
1 16 10 0 10
2 12 7.5 2.5 10
3 8 5 5 10
4 4 2.5 7.5 10
5 2 1.25 8.75 10
6 0 0 10 10
2. I transferred each solution from each test tube into a cuvette.
3. The 520mm filter was placed into the colorimeter.
4. Cuvette 6 (which is water) was placed into the colorimeter and calibrated to 0.
5. Samples 1-5 were placed in the colorimeter and readings were recorded.
6. To find the concentration of red dye in the 2 forensic samples, 2 more cuvettes with
forensic samples A and B were placed into the colorimeter and the absorbance was
recorded.
7. A graph was plotted and used to find the concentration of red dye in forensic samples A
and B.
Laboratory report
Investigation into the concentration of red diesel
Aim - carry out experiments to:
● To find out the correct wavelength filter to use with a red diesel solution
● Prepare a standard curve
● Determine the concentration of red diesel in different samples
Abstract
The concentration of dye in the forensic samples A and B was measured using the method
colorimetry to determine absorbance wavelengths. At full strength the dye in red diesel is 10
mg/cm3. The concentration of dye of the sample A was 7.8 mg/cm3 and this shows that the
solution was watered down. The concentration of dye of the sample B was 1.8 mg/cm3 and this
shows that the solution was also watered down.
Introduction
This practical uses the Beer-Lambert law which states that when light passes through a
coloured solution, some of the light will be absorbed. The amount of light absorbed is dependent
on the concentration of the solution, therefore the darker the solution, the higher the
concentration and the more light that will be absorbed. For coloured solutions, you need to use
a specific color or wavelength of filter to give the optimum absorbance.
For example, with a green filter - white light will be directed through a filter and green light will
be transmitted through the filter which makes the filter green. Other wavelengths will be
absorbed into the solution. In this case, the beer-lambert law can be used to find out whether
the red diesel has been watered down.
Equipment
● A standard solution of dye at 16mg cm-3
● A colorimeter
● Appropriate filter
● Cuvettes
● Cuvette rack
● Glass pipettes
, Unit 1 assignment 6
● 6 Test tubes
● Test tube rack
● 2 forensic samples
● Marker pen
Method
Preparation of solutions for the standard curve
1. A variety of solutions of different concentrations of red dye were prepared to cover a
concentration range of 0-16mg/cm3. These were prepared using a dye at 16mg/cm3 and
water shown in the table below:
Tube Concentration Volume of red Volume of Total volume
of red dye dye required at water required
(mg/cm3) 16mg/cm3 (cm3)
1 16 10 0 10
2 12 7.5 2.5 10
3 8 5 5 10
4 4 2.5 7.5 10
5 2 1.25 8.75 10
6 0 0 10 10
2. I transferred each solution from each test tube into a cuvette.
3. The 520mm filter was placed into the colorimeter.
4. Cuvette 6 (which is water) was placed into the colorimeter and calibrated to 0.
5. Samples 1-5 were placed in the colorimeter and readings were recorded.
6. To find the concentration of red dye in the 2 forensic samples, 2 more cuvettes with
forensic samples A and B were placed into the colorimeter and the absorbance was
recorded.
7. A graph was plotted and used to find the concentration of red dye in forensic samples A
and B.
