Question

A stock phenolphthalein solution was prepared by dissolving 0.050 g in a total volume of 100.0 ml. You place one drop (0.050 ml) of this stock solution into a flask and dilute to 100.0 ml. The measured absorbance of this diluted sample is 0.18. What is the value of molar absorptivity, ε?

Answer 1

the value of molar absorptivity is 229000
`M^(-1) cm^(-1)`

Step-by-step explanation:

given data

phenol phthalein solution = 0.050 g

total volume = 100.0 ml

dilute = 100.0 ml

diluted sample = 0.18

solution

we get here concentration that is express as

concentration = ( mass of solute × 1000 ) ÷ ( molar mass of solute × volume of solution ) .............1

put here value

concentration =
`(0.050* 1000)/(318.32* 100)`

concentration = 0.00157 M

and here dillution equation is express as

c1 × v1 = c2 × v2 .................2

here c1 and c2 is initial and final concentration

and v1 and v2 is initial and final volume

put here value

0.001571 × 0.050 = c2 × 100

c2 = 7.855 ×
`10^(-7)` M

and

now we get molar by absorbance equation that is

A = E × C × l ................3

here A is absorbance and E is molar and c is absorptivity and l is path length

put here value

0.18 = E × 7.855 ×
`10^(-7)` × 1

E = 229000
`M^(-1) cm^(-1)`