A 25.00 mL solution of potassium nitrate (KNO3) was diluted to 125.0 mL, and 25.00 mL of this solution were then diluted to 1.000 103 mL. The concentration of the final solution is 0.00421 M. Calculate the concentration of the original solution.

Answer 1

There are two ways to solve this dilution problem; i.e., forward or backwards. Backwards first.
0.00421 x (1000/25) x (125/25) = ?

The forward way is this.
x*(25/125)*(25/1000) = 0.00421 and solve for x, the beginning concn.