When 7 mL of a solution containing 4 M KNO3 is diluted to 23 mL, a dilute solution is formed. What is the NO3- concentration in 15 mL of the dilute solution?

Answer 1

4M KNO3 x (7 mL/23) = ?M KNO3.
Since there is 1 mol K^+ and 1 mol NO3^- in 1 mol KNO3, then ?M KNO3 = that M NO3^-. The NO3^- is the same whether you are viewing 1 mL or 20 mL, moles/ L is the same.