The Science Of Colorimetry

1
The Science Of Colorimetry

• Quantitative Iron Determination Practical

2
What is Colorimetry?

• The colour of a solution depends on the amount of
  the substance dissolved

Copper Sulphate
3
Beers Law
A e.c.l

• e is a constant
• (molar absorptivity- light absorbed by 1cm3 of a
  1M soln)
• c is the concentration
• l is the path length through the soln
• By using the same size cell throughout experiment
  
• l remains constant
• A?c

4
Colorimetry

• Absorbance is proportional to the concentration
• Higher absorbance means a higher concentration
  and a more intense colour
• By measuring the light absorbed we can determine
  the concentration of a solution

5
Spectrophotometry
Iron Standard
40mg/dm3
?20 Dilution
?50 Dilution
?100 Dilution
?10 Dilution
2mg/dm3
4mg/dm3
0.8mg/dm3
0.4mg/dm3
6
Spectrophotometry
N
N
Fe2
Fe2
N
N
Max ? 508nm
0-phenanthroline
7
Spectrophotometry
8
Practical Instructions

• Method (a) describes how to prepare the standard
  solutions for the calibration curve
• Method (b) describes how to prepare sample
  solutions of unknown concentration from the iron
  tablet provided
• Method (c) describes how to read the absorbance
  of the standard and sample solutions using a
  spectrophotometer

9
Results
The actual mass of the iron in the tablet was
0.704g (704mg)