[chmdummy1982]

I am having trouble with a couple of chemistry problems. One I was able to answer half of, and the other I don't even know how to start. Any help would be greatly appreciated!


Question 1

Use the dilution relationship (Mi x Vi = Mf x Vf) to calculate the volume of 0.500 M NaOH needed to prepare 500 mL of 0.250 M NaOH.

? mL x .500 M NaOH = (500mL x.250M)/.500 = 250 mL


Now here is where I am lost with this problem:

What volume of water would you add to the 0.500 M NaOH volume calculated aove to actually make 500 mL of 0.250 M NaOH?


Question 2
49.22 mL of a 2.01 M NaOH solution reacts completely with 40.28 mL of HCl solution according to the balanced chemical reaction shown below:

HCl (aq) + NaOH(ap) -> NaCl(aq) + H2O(i)

How many moles of HCl reacted?

[Astrokel]

What volume of water would you add to the 0.500 M NaOH volume calculated aove to actually make 500 mL of 0.250 M NaOH?

You have calculated it! 250mL

How many moles of HCl reacted?

Check this out, one of this forum admin's website: http://www.chembuddy.com/?left=balancing-stoichiometry&right=ratio-proportions

[chmdummy1982]

So heres my work.

(40.28 / 49.22) x 2.01 = 986.3590  (thousandths place)

would this be correct?

[Astrokel]

Nope, they are asking for moles of HCl reacted. How do you calculate moles? Any formula you known of that could be apply to this question?

[chmdummy1982]

Would the molarity formula have anything to do with it?

M = moles of solute/Liters of solution

I'll give it another shot..

(49.22 x 2.01)/40.28 = 2.4561

[Astrokel]

M = moles of solute/Liters of solution

I'll give it another shot..

(49.22 x 2.01)/40.28 = 2.4561

Formula correct, working wrong. What you are calculating is molarity but they are asking for moles.

[chmdummy1982]

Would I have to use this equation??

moles = M X V?

[Astrokel]

Yes