Question

3. If a mixture was prepared by diluting 7.0 mL of the Blue#1 solution with water to a final volume of 10.0 mL and mixing this with 2.0 mL of diluted bleach how many seconds would it require for the mixture to have an absorbance of 0.120? Use your measured values of epsilon b and of the average rate constant, k to answer this question. Show all work

Ok so I have m1v1=m2v2 for this which is 15M(7)= m2(12ml)

m2=8.75M

my epsilon b= =.1044

and my k= -0.0351

its a first order reaction. Please help me figure out this question

Answer 1

you have to use equation

M1V1 = M2V2

and M2 = 8.75 M(according to you )    b=.1044 , k= -0.0351

as we know that for first order equation is given by

we have to calculate time at which absorbance becomes zero . so we first calculate that concerntration at which it s absorbance becomes 0.120 . then we put that concentration in our first order rate equaion to find out the time taken to reach that concentration .

A = C l= .1044 * C * 1 cm = 0.120

C = 0.120 /  .1044 = 1.149 is the concentration at which absorbance is equal to = 0.120

first order equation is given by

k = 2.303 / t log [A₀] /[A]

where ,[A₀] = 8.75 ( mixture initail concentration ) and [A] = 1.149 ( final concentartion )

t = 2.303 / -0.0351 log 8.75 / 1.149

t= 2.303 / -0.0351 log 7.61

= 2.303/ 0.0351 * ( 0.8813 ) = 57 seconds