How do I calculate the concentration of...?

Question

8 mL of 8.00 x 10^-3 LAS solution in 42 mL of distilled water? What is the LAS concentration?

LAS is Lauryl Aryl Sulfonate (a.k.a. sodium dodecylbenzenesulfonate or C18H30O4S. Na)

Please tell me the steps involved to get the answer. Thanks!

Answer 1

I'm assuming the 8e-3 (8x10^-3 shorthand) LAS solution is 8e-3 M. SO molarity (M) = moles/liter. so you want to find out how many moles you are adding to the distilled water first:

so 8 mL is .008 L. so 8e-3M = X moles/.008 L. Solve for X and you get 6.4e-6 moles of LAS.

The concentration in the water is going to be moles of LAS over Liters of solution. So 6.4e-6/(.042+.008) = Z, solve for Z and you get your answer. (1.28e-4) or 1.28x10^-4 M

Above you added .042 + .008 because you want the total volume of the solution (.042 L water + .008 L LAS)

* I didn't use a calculator so you might want to check my numbers, but this is how you solve it.

Good luck!

Answer 2

MV=n

Molarity times Volume(in liters) equals moles

you can set two different MVs equal to each other

MV1=MV2