An 7.50 mL aliquot of a 125 ppm stock Red 40 dye solution was diluted to a final volume of 25.0 mL with deionized water. What is the concentration of the dilute Red 40 dye solution (in ppm)?

The concentration is equal to 37.5 ppm

Explanation:

This exercise is about dilutions. We have the following data:

V1 = aliquot volume = 7.5 mL

C1= aliquot concentration  = 125 ppm

V2 = final volume = 25 mL

C2 = final concentration of Red 40 dye = unknown

the formula is as follows:

V1xC1 = V2xC2

Clearing C2:

C2 = V1xC1/V2 = (7.5 mL x 125 ppm)/25 mL = 37.5 ppm