1 a To prepare her Beers Law plot Susan followed instruction

1. a) To prepare her Beer\'s Law plot Susan followed instructions and read the absorbances of her standard solutions promptly after they were prepared. Anna prepared her standard solutions. But spent fifteen minutes calculating the concentrations before she finally measured the absorbances. Anna\'s slope was much lower than Susan\'s. Explain why b) Both Susan and Anna prepared their equilibrium mixtures and read the absorbances promptly. Each used her own Beer\'s Law plot to find the equilibrium concentrations of FeSCN, Fe\", and SCN and then the value of the equilibrium constant. Is it likely that they got similar values for K. Or was one greater than the other? If so, which? Explain your reasoning. eq

Solution

a )The slope in beer\'s law plot is the product molar extinction coefficient and the path length (€ × l)

So if Anna\'s sope was much lower means she would have used the solution with less molar extinction coefficient or the path length she used for measuring must have lower length ( l )

Extinction coefficient can be less when the concentration is less and so Anna woud have used lesser concentration

b) The beer\'s law equation is

A = € × l × c

A - absorbance

€ - molar extinction coefficient

l - path lenght

c - concentration

From this equatiom we can calculate the equilibrium concentration and also the equilibrium constant

c = A/slope ( slope = € × l )

Here we know Anna\'s slope is lower than Susan\'s

So Anna will get higher equilibirum concentration for FeSCN²⁺ form beer\'s law plot and also the higher K_e than Susan

K_eq = [FeSCN²⁺] / [Fe³⁺] [SCN^-]