Question

A solution was diluted by a factor of 2 and then again using a 1 to 3 dilution. What is the dilution of concentrate in the final sample

Answer 1

How do you expect a chemistry expert to answer your question when you don't type your subject in the School Subject box?

Answer 2

A solution was diluted by a factor of 2 and then again using a 1 to 3 dilution. What is the dilution of concentrate in the final sample or

If 15ul of a 4% solution is diluted up to 50ul, what is the concentration of the resulting solution? Include units with your answer

Answer 3

Frankly, there is so much confusion about what 1 to 3 dilution means that I never use it. Approximately 50% believe 1:3 means add 1 part solute to 3 parts solvent while the other half thinks it means 1 part solute to a total of 3 parts.
So a factor of 2 means it was diluted to 1/2 of the original volume. Let's just say we had a concn of 10 mg/mL. Diluted by a factor of 2 means we have reduced the concn to 1/2 x 10 mg/mL = 5 mg/mL. Now if we add 1 part of the 5 mg/mL plus 3 parts solvent, we have 1/4 of 5 mg/mL = 1.25 mg/mL ASSUMING that the volumes are additive and they probably are at weak strengths. I know I will get a lot of feedback on this BUT I believe 1:3 SHOULD mean 1 to a total volume of 3. When we say dilute 1:10 almost everyone understands that to mean to take 1 mL (measured with a pipet) and add water to a total volume of 10 mL (with a volumetric flask). This way we don't worry about the volumes being additive or not. So a 5 mg/mL solution diluted 1:3 means we have 5 x 1/3 = ?? you figure it. So those are the two ways of doing it. Take your pick depending upon what you've been taught.

Answer 4

For the other problem, it is not that ambiguous (except that we don't know if it is percent by volume or percent by mass).
4% x (15 uL/50 uL) = ??%