SPECTROPHOTOMETRY

What is the light absorbed proportional to?

the concentration of the absorbing species

What is added to complexes with pale colours so they absorb light stronger?

suitable ligands are used to intensify the colour

What is the method to find the concentration of a substance using absorption?

1. add an appropriate ligand to intensify the colour

2. make up solutions of known concentration

3. measure absorption

4. plot a graph of absorption vs concentration

5. measure absorption of unknown and compare

What must spectrometers contain?

a coloured filter which is chosen to only allow the wavelengths of light through that would be most strongly absorbed by the coloured solution

What is the method to find the absorption of an unknown copper solution?

1. take 9 100cm³ graduated flasks and pipette 20cm³ of 2 moldm^-3 ammonia solution into each one. use 0.05 M of aqueous copper sulfate to make up solutions which are concentrations of 0.005 to 0.04

2. mix each solution thoroughly

3. insert the red filter into the colorimeter

4. use a cuvette with distilled water to zero the colorimeter

5. put each prepared solution in cuvette and measure the absorbance of each solution

6. plot a graph of absorption vs concentration

7. measure absorption of unknown solution and determine its concentration from the calibration curve