[Duzzy]

1 mL of 1 mM KCl solution was mixed with 9 mL of 0.01 M CaCl2 solution. The final
Cl- concentration is:
A. 18.1 mM
B. 9.1 mM
C. 1.81 mM
D. 0.91mM
E. 181mM

Ok, so I do this:

0.001 (0.001) you get 1x 10^-6 + 0.009x 0.01 x 2 = 1.81x10^-4

the study guide states that the answer is A

[Borek]

So far you calculated only amount of chlorides, not their concentration.

[Duzzy]

so you divide 1.81 x 10^-4 / 0.01 (10mL which is the total volume of the solution) and that's the answer, right?

[Borek]

Yes.