Quick Notes Colorimetry
- Colorimetry is a technique used to find the concentration of a solution based on the intensity of light (of a specific wavelength) it absorbs or scatters.
- Coloured solutions absorb specific wavelengths of visible light. The more concentrated a solution is, the greater the intensity of light it absorbs.
- The amount of light that passes through a sample is detected, giving an indication as to the amount of light absorbed by the sample.
- A calibration curve is made using the absorbances of solutions of known concentrations.
- The absorbance of the unknown concentration is compared to the calibration curve, and the concentration is found.
Full Notes Colorimetry
The intensity of light absorbed by a coloured solution is dependent on the concentration of the solution. The greater the concentration of a solution, the greater the intensity of light absorbed by it. Colorimetry is a technique used to find the concentration of a solution. The intensity of light absorbed by a sample with an unknown concentration is measured, then compared to the absorbances for known concentrations of the same substance, using a calibration curve.
Colorimeters measure the specific wavelengths of light absorbed or scattered by a sample, enabling graphs (spectra) to be formed that are unique to every substance and concentration of solution.
A colour filter is used to remove the wavelengths of light not absorbed by the solution.
![colorimetry colour filter detector transition metal a-level chemistry](images/A2Inorganic/transitionelements/transitionelementscolorimetry1.png)
The greater the concentration of solution, the greater the intensity of wavelengths absorbed by the solution (in this example, orange light).
![absorbance of light colorimetry a-level chemistry](images/A2Inorganic/transitionelements/transitionelementscolorimetry2.png)
The intensity of the wavelengths detected are related to the concentration of the sample.
![colorimetry dilute solution](images/A2Inorganic/transitionelements/transitionelementscolorimetry3.png)
![colorimetry concentrated solution](images/A2Inorganic/transitionelements/transitionelementscolorimetry4.png)
The intensity of absorption for the solution is measured for known concentrations.
![calibration curve colorimetry a-level chemsitry](images/A2Inorganic/transitionelements/transitionelementscolorimetry5.png)
The results are plotted on a graph and a line of best fit is drawn. This is called a calibration curve.
![using calibration curve colorimetry a-level chemistry](images/A2Inorganic/transitionelements/transitionelementscolorimetry6.png)
The results for the original solution with an unknown concentration are obtained and compared with the calibration curve, and the concentration is found.