so would this mean I would do (0.26244391 mols HCL) / (2 Liters)

and then multiply that by 2.5? Sorry if I sound stupid but this is perhaps the hardest subject I've ever taken and I've taken about a doze senior level classes before this.

No, that 2 liter volume has nothing to do with the problem at this point.
With pv=nrt you found how many moles of h2 you had
from the coefficient in the balanced equation, you foudn how many moles of HCl is needed

With n_HCl known, you can calculate how many mili liters of "2.5 M HCl" is needed

If it was 1 M HCl and you needed 2 moles of HCl, that would mean you need 2 liters
If it was 2 M HCl and you needed 2 moles of HCl, that would mean you need 1 liter

So would that mean that I need .8 Liters, or 800 ml?

This post was edited by chicano on Jun 25 2015 08:03pm

So you calculated that you need 0.262 mols of HCl
M=m/L
2.5 = .262 / L

L= .262/2.5 = .105 L => 105 mL

It might be more intuitive to just say

I need .262 mols of HCl
What I currently have is 2.5M, meaning it's 2.5 the normal strength
if it was normal strength (1M) you would need .262 liters
to account for the extra strength, just divide by the molarity M

This post was edited by saber_x3 on Jun 25 2015 08:13pm

Awesome, before you responded a friend of mine helped me figure it out as well and he got 104.98 ml so basically what you gave me too!

If you don't mind, I just have one last one that I need help with. Would really appreciate it if you helped me out!


You collected 220 grams of Carbon Dioxide gas over water at STP. What is the partial volume of Carbon Dioxide? What is the mole fraction of water?


I'm assuming at STP, temperature = 273.15 kelvin and pressure is 1 atmosphere.

220g of carbon dioxide = 4.998886612 mols

This post was edited by chicano on Jun 25 2015 08:41pm

I think the question is incomplete,
It should be mole fraction of water "vapor" ?


The total pressure given is P_tot = P_co2 + P_h2ovapor
Do you know how to look up the pressure of the water vapor?

Hey I ended up just turning it what I had since it was due online yesterday at 10pm and my time was almost up. Thanks a lot for your help though, you helped a ton!