Question

You come into lab and notice your lab partner did a 1:10 dilution series on a stock that you ordered. You see that the final dilution has a concentration of 0.0004 Molar and that your partner had diluted the stock seven times. What is the concentration of the original stock solution?

is it 40,0000?

Answer 1

First method:

Stock solution is diluted seven times. First time it is diluted, the dilution is 10^-1 or 1: 10 dilution. Hence, final dilution is 10^-7 dilution.

Final dilution= 10^-7

Final concentration= 0.0004M

Initial concentration= ?= A

Initial dilution =10⁰=1

C1D1= C2D2

A X 1= 0.0004M X 10⁷

A= 4000M

Another method

7th dilution= 10^-7 dilution = 0.0004 M

6th dilution=10^-6 dilution = 0.004 M

5th dilution=10^-5 dilution = 0.04 M

4th dilution=10^-4 dilution = 0.4 M

3rd dilution=10^-3 dilution = 4 M

2nd dilution=10^-2 dilution = 40 M

1st dilution=10^-1 dilution = 400 M

10⁰ dilution = Stock solution= 4000 M

Right answer= 4000 M