Question

A mouthwash, which comes in a concentrated syrup, contains red dye 40. The red dye 40 syrup is diluted by a factor of 2 three times. If the red dye 40 concentration is `6.60xx10^-3" M"` in the original syrup, what is its concentration in dilution 3?

Answer 1

Well, if we dilute by half we get HALF the original concentration....

Explanation:

And we dilute THIS solution by half we get ONE QUARTER of the original concentration....

i.e. `1/2xx1/2=1/4`, and we dilute this solution AGAIN, we get `1/2xx1/2xx1/2=1/8` with respect to original concentration.

And for `n` such serial dilutions we got `1/2^(n+1)` WITH RESPECT to the initial concentration. Here we made 2 dilutions....and so we got `1/2^3=1/8`

And for `"red dye 40"` we got `1/8xx6.60xx10^-3*mol*L^-1=8.25xx10^-4*mol*L^-1`