CH 202 Problem 4.74

4.74 (a) How many mL of a stock solution of 10.0 M HNO₃ would you have to use to prepare 0.450 L of 0.500 M HNO₃?

You should recognize this as a dilution problem. In this type of problem, we use the relation

M_concV_conc = M_dilV_dil

where M_conc = molarity of concentrated solution, V_conc = volume of concentrated solution, M_dil = molarity after dilution, and V_dil = volume of diluted solution.

A look at the numbers given in the problem reveals that we are trying to make up 450 mL (0.450 L) of 0.500 M HNO₃; this is the volume and molarity of the dilute solutions, respectively. The molarity of the concentrated solution is 10.0 M; what we are trying to find is the volume of concentrated (10.0 M HNO₃) solution which we need to dilute to 450 mL to get 0.500 M HNO₃; thus, we are trying to find V_conc in the relation above.

so,

(b) if you dilute 25.0 mL of the stock solution to a final volume of 0.500 L, what will be the final concentration of the diluted solution?

We use the relation given above, and we solve it for M_dil, molarity of the diluted solution. We're given two volumes and the molarity of the concentrated stock solution (10.0 M), so this is pretty strightforward:

DAC 7/7/08