Molarity in diluted solution

1. Apr 28, 2004

nemzy

Lets say you pipet into a 250 mL volumetric flask the following:

10 ml of 3e-4 M bromscresol green solution
25 mL of 1.6 M acetic acid (HC2H3O2)
10 mL of .200 M KC1 Solution

and diluted to the 250 mL mark

What is the molarity of acetic acid in this solution?

Do you calculate the number of moles in the 25 mL solution since you know the molarity, then when u get the moles you find molarity over 250 mL?

2nd problem.. Lets say you have a solution with the following:

10 mL of 3e-4 Bromscresol green solution
10 mL of .160 M sodium acetate solution
and diluted to 250 mL mark

What is the mles acetate present?

Do you calculate the # of moles over just 10 mL?

Does the # of moles stay constant even though you add more volume? I think i heard that somewhere but not sure

2. Apr 28, 2004

KLscilevothma

Yes, this is the way we tackle the problem.

] Yes, you need to calculate the number of moles of sodium acetate in 10mL first.

Yes. Number of moles tells you the number of molecules present and the number of molecues will not change upon dilution. Let me give you an analogy. If there are 3 balls in a cylinder containing 50mL water, you cannot change the number of balls inside by adding more water into the cylinder.