Intermediate Topic 915 of 1102 Analytical, Lab & Spectroscopy
Colorimetry
Measuring concentration of colored solutions by absorbance of light.
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In-depth explanation of Colorimetry
Colorimetry determines the concentration of a coloured solution by measuring how strongly it absorbs light at a wavelength where the coloured species absorbs most strongly. A filter or monochromator selects the wavelength, and the absorbance of the unknown is compared with that of standards of known concentration, usually through a calibration curve. Colourless ions can be converted into strongly coloured complexes by adding a suitable reagent, which extends the method to many metal ions. The method is simple, inexpensive and suitable for routine work, although interference from other coloured species must be controlled. Consistent cell path length and a reagent blank are important for accuracy.
Going deeper: Colorimetry
Key ideas: Pick a filter complementary to the colour of the solution. Prepare a series of at least five standards plus a blank, develop colour for a fixed time under identical conditions, then plot absorbance versus concentration. The blank is the reagent without analyte. Known colour-forming reactions: Fe3+ with thiocyanate (red), Cu2+ with ammonia (deep blue), phosphate with molybdate (blue).
Common mistakes and connections: Typical errors include varying colour development time, using wrong cell orientation, and measuring unknowns outside the standard range. A turbid sample scatters light and gives falsely high absorbance. Overlapping absorption of other species interferes, so run a sample blank. Students forget that coloured complexes may be unstable or pH sensitive. Related to Beer-Lambert, calibration curve and spectrophotometer design.
Visualization of Colorimetry
The red iron thiocyanate complex absorbs most near 480 nm, the wavelength chosen for colorimetric iron determination. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Iron is determined by forming the red thiocyanate complex and measuring its absorbance near 480 nm.
Frequently asked questions about Colorimetry
What is Colorimetry?
Measuring concentration of colored solutions by absorbance of light.
Is Colorimetry a beginner, intermediate or advanced topic?
Colorimetry is a intermediate topic in Analytical, Lab & Spectroscopy. It builds on the vocabulary of beginner topics in this area.
What should I learn before Colorimetry?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Fragmentation Patterns, UV-Visible Spectroscopy, Beer-Lambert Law.
What comes after Colorimetry?
The next topics in Analytical, Lab & Spectroscopy are Calibration Curve and Infrared Spectroscopy.
Can I practise Colorimetry with quizzes?
Yes. The interactive lesson includes a self-check question on Colorimetry, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where Colorimetry fits in Analytical, Lab & Spectroscopy
Colorimetry is topic 39 of 99 in Analytical, Lab & Spectroscopy.