A solution is prepared by placing 23.9 g of KCl in a 0.500 L volumetric flask and adding water to dissolve the solid, then filling the flask to the mark. What is the molarity of an AgNO3 solution if 27.9 mL of the KCl solution react exactly with 45.0 mL of the AgNO3 solution?

Answer 1

mols KCl = grams/molar mass = approx 0.32 g but you need a more exact number for this and all of the estimates that follow.
M KCl = 0.32/0.5L = about 0.64

Then mL x M = mL x M
27.3 x 0.64 = 45.0 x M AgNO3
Solve for M AgNO3.
The mL x M = mL x M works because the equation is 1:1.
AgNO3 + KCl ==> AgCl + KNO3