[student8607]

Sulfuric acid is normally purchased at a concentration of 18.0M. How would you prepare 250.0mL of 0.500M aqueous H2SO4?

Mf = Mi x (Vi/Vf)

Mf = 18.0M
Vi = 250.0mL
Mi = 0.500M

perhaps you can rearrange it to be
---> (1/Vi) x (Mf/Mi) = Vf?

0.036mL?

[Borek]

You are most likely looking for Vi, not Vf (although it doesn't matter much, equation you are using can be written as C₁V₁ = C₂V₂, it is not some kind of special formula, it just mass balance - number of moles before dilution is identical to number of moles after dilution. Doesn't matter what is 1 what is 2, as long you know which is which).

But final result is wrong.

[student8607]

6.94. That is correct!

Thanks

[Omggg]

um, im pretty sure you have to convert the volume to liters before doing the molarity calculations

so you would actually get
=6.94*10^-3 mol/L
= 0.00694 mol/L

[Borek]

um, im pretty sure you have to convert the volume to liters before doing the molarity calculations

Not necesarilly. If you look at units you will find out that concentrations cancel out and you are left with the same unit of volume you have entered.

That's a shortcut, but a correct one. You just have to know what you are doing and why you can

It doesn't mean you can always use mL. Converting to L is safer, but even if you don't - you still can get correct answer, you just have to be careful.

Let's say we have 20 mL of 0.1M solution. How many moles of substance?

With conversion:

0.02L * 0.1 = 0.002 mole - obvious and correct result.

without conversion:

20 mL * 0.1M = 2 - looks wrong - but you just have to remember that the result now is in millimoles, not moles. That's kind of a 'hidden conversion'.

Kids don’t try this at home or in public places. We are trained proffesionals

[Omggg]

why don't you guys just give the man his correct answer, instead of making him even more confuse,

obviously this is gr 11-12 chemistry, and he doesn't know much.

[Borek]

why don't you guys just give the man his correct answer, instead of making him even more confuse

He already found correct answer on his own, please reread the thread. Besides, just giving correct answers is against forum rules.

[Arkcon]

why don't you guys just give the man his correct answer, instead of making him even more confuse,

obviously this is gr 11-12 chemistry, and he doesn't know much.

We try not to do that here, and not just because it's against the forum rules.  If we dump free answers on this forum, the only people who will want to come here are people looking for an easy A.  Then, they'll be no one available to answer questions, heh. 

[JGK]

why don't you guys just give the man his correct answer, instead of making him even more confuse,

obviously this is gr 11-12 chemistry, and he doesn't know much.

Yeah and if we spoon feed him answers, he'll learn zip.  When I was that age my chem teachers favourite follow up to a correct answer in  class whas either "why?" or "how?". that way he knew you understood stuff rather than guessing.

Understanding the fundamentals is essential to progress further in any meaningful way.

[student8607]

Understanding the fundamentals is essential to progress further in any meaningful way.
[/quote]

Amen to that!