Question

A chemist was asked to determine the concentration of zinc in plant extract.the chemist dissolved 1 gram of the plant extract in 100ml flask using appropriate solvent and filled it to the mark using deionized water.the solution gave absorbance of 0.46.if the molar absorptivity of the solution was 3.65*10^4L/M/cm and th path length 1cm calculate concentration of zinc in moles per gram

Answer 1

molar absorptivity of solution (ɛ) = $3.65×10^4L/mol·cm$

absorbance (A) = 0.46 Au

Path length (l) = 1 cm

• The standard equation for absorbance is A = ɛ x l x c

1. A is the amount of light absorbed by the sample for a given wavelength
2. ɛ is the molar absorptivity
3. l is the distance that the light travels through the solution or the path length
4. and c is the concentration of the absorbing species per unit volume

• Plugging in what we know:

$c= \frac{A}{ɛ × l}$

$c = \frac{0.46}{(3.65×10^4× 1)}$

$c = 1.26×10^{-5}mol/L$