A LevelChemistryAQARevision Notes8. A-Level Practical Skills (A Level only)8.2 Inorganic Chemistry Practicals (A Level only)8.2.6 Colorimetry & Complex Ions

Colorimetry & Complex Ions (AQA A Level Chemistry)

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Stewart

Last updated

25 November 2021

Colorimetry & Complex Ions

Colorimetry can be used to measure the absorption of radiation using a colorimeter
This uses a lamp as a source of white light, which passes through a filter to produce light of one colour
- This colour will be the one that the sample will absorb the most and is called its complementary colour
For example hexaaquacopper(II) solution is a pale blue colour which absorbs red light
It's complementary colour is blue which is what is transmitted

A simple diagram representing the component parts involved in colorimetry

Worked example

Outline a practical method for the preparation of an unknown concentration of metal aqua ion solution by colorimetry.

Answer:

- Make up metal aqua ion solutions of known concentrations
- Measure absorption or transmission
- Plot a calibration curve (absorbance vs concentration)
- Measure absorption of unknown
- Determine concentration of unknown

Visible Spectroscopy Calibration Curve, downloadable AS & A Level Chemistry revision notes

Calibration curve from colorimetry results, showing the absorbance of an unknown being used to determine the concentration

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Author: Stewart

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.