Question

umill) reacts with a bipyridine molecule in solution to give the following mole ratio data Ceriu Mole Ratio Absorbance (mol bpy/mol Ce) Solution 0.044 0.168 0.5 0.288 0.416 0.419 0.422 0.425 0.426 0.427 0.428 1.5 2.5 What is the mole ratio of bpy/Ce3 in this reaction? 5. Suggest a formula for the complex (include only Ce, bipy and the charge). You may write an equation. Hint: If the ratio is not a whole number you may need to multiply to obtain an acceptable ratio and more than answer may apply)

Answer 1

4)This problem is completely based on the Lambert-Beer Law.This law establishes a relationship between the absorbance (A) and the molar concentration of the solution.According to this law:

A = $\varepsilon$ l c, Where $\varepsilon$ = the molar absorptivity or the extinction coefficient for the absorbing material(is unique ( in M^-1 * cm^-1 ) for each material)

l = sample path length ( in cm) and

c = molar concentration of the solution

Now coming to the problem, since $\varepsilon$ and l are constant, we have

A₁ / A₂ = c₁ / c_{2 ,} Hence we get the molar ratio of bpy/ Ce⁺³ = 1.5

b) Now since the ratio isn't a whole number, we multiply it by 2 to get the empirical formula of the compound :

Ce₂(bipy)₃ , So that's the required formula of the compound.