# Question dfb12

Feb 9, 2015

The concentration of PNP is 180 µmol/L.

We have to assume that the volume does not change when you add the PNP to the NaOH solution. If the volume changed by ±1.25 µL, the change would be ±1 %. You should check with your instructor if this assumption is allowed.

Step 1. Calculate the concentration of PNP before dilution.

$\text{Moles of PNP" = "1.25 mg PNP" × "1000 µg PNP"/"1 mg PNP" × "1 µmol PNP"/"139 µg PNP" = "8.99 µmol PNP}$

$\text{[Molarity](http://socratic.org/chemistry/solutions-and-their-behavior/molarity)" = "moles"/"litres" = "8.99 µmol"/(1200 × 10^-6"L") = 7.49 × 10^3"µmol/L}$

Step 2. Calculate the concentration of PNP after dilution.

You added 12.0 µL to 488 µL, so your new volume was 500 µL. Now we do a simple dilution calculation.

c_2 = 7.49 × 10^3"µmol/L" × "12.0 µL"/"500 µL"= "180 µmol/L"#