Question

Calculate the final concentrations of the following aqueous solutions after each has been diluted to a final volume of 25.0 mL:
a. 3.00 mL of 0.175 M K^+
b. 2.50 mL of 10.6 mM LiCl
c. 15.00 mL of 7.24 * 10^-2 mM Zn^2+
the answers are A) 0.0210 M Na^+, B) 1.28 *10^-2 mM LiCl, C) 1.28*10^-2 mM Zn^2+
I don't understand how they get these answers

Answer 1

I use this.
0.175 M x (3.00/25.0) = ?

You can use the dilution formula of
mL1 x M1 = mL2 x M2
3.00 x 0.175 = 25.0 x M2 and solve for M2. Both will give you the same answrs.

Answer 2

The answers I got for the formula are not the correct ones.

Answer 3

Then you made a math error because
3.00 x 0.175 = 25.0 x M2 solves to
M2 = 3.00 x 0.175/25.00 and that's the same as 0.175 x 3.00/25.0 = ?

Answer 4

0.0186 M