posted by Allie .
how many milliliters of 0.10 M HCl must be added to 50.0 mL of 0.40 HCl to give a final solution that has a molarity of 0.25 M?
work with the moles.
x ml of .1M HCl has .0001x moles HCl
50ml of .40M HCl contains .05*.4 = .02M HCl
(x+50)ml of .25M HCl contains (x+50)/1000 * .25 = .00025x + .0125 M of HCl
so, the moles need to add up:
.0001x + .02 = .00025x + .0125
x = 50
since equal amounts of .1M and .4M acid are mixed, the concentration will be the average of .1 and .4, or .25