Colorimetric determination of
manganese in steel
Colorimetric analysis
• type of visible spectroscopy
• used to determine the concentrations of
coloured solutions
• coloured substances absorb light of a colour
complementary to their own
• a single wavelength of light is used
• the amount of light absorbed is proportional to
the concentration of the substance
Colorimetric determination of manganese
in steel
Manganese in steel can be converted into permanganate
ions by oxidising with
- nitric acid, Mn(s)
Mn2+(aq) + 2e- potassium periodate,
Mn2+(aq) + 4H2O(l)
MnO4-(aq) + 8H+ + 5ethe colour develops during the second step; the mixture
should be heated until the intensity of the pink colour
remains constant
permanganate solution appears purple because it absorbs
green light and transmits red and blue thus a green filter
(520 - 550 nm) is used
Colorimetric determination of manganese
in steel
Optically matched cuvettes are used to ensure that any
absorption by the cuvette is kept constant
A calibration curve is prepared where the absorbance of
known concentrations of permanganate is measured