[GreyMan]

I'm having trouble understanding what seems to be a simple stoichiometry problem. I reacted 15 ml of HCl with 0.1 g of Mg to get MgCl2 and H2. I need to calculate the amount of H2 in ml produced.

When I try to do the work, I just don't understand what 1 mol of HCl is. How do I take 15 ml of HCl and turn it into moles? Do I need to know the concentration of the HCl in the water to determine this or am I missing something else?

Thanks

[Arkcon]

Yes, you will need some measure of the concentration of the HCl in solution, unless you were working with HCl gas.

[GreyMan]

I believe it was a 38% solution in water. Where do I go from here?

[Borek]

If it was %, you will need density as well.

Not exact, but close...

http://www.chembuddy.com/?left=CASC&right=density_tables

[GreyMan]

So HCl is about about 1.2 g/mL at a 38% concentration. If there are 15 mL, that means there are 18 g of HCl. I'm confused. Now, how exactly do I find how many mL are in one mol of HCl?

[Borek]

Now you calculate masss of HCl, then you convert mass to moles.

[GreyMan]

I'm really not sure how do to this. I'm pretty new to this. Can you explain this?

[Borek]

HCl is 38% of 18 g.

1 a.m. here. Logging out.

[Arkcon]

Use the formula mass of HCl as a conversion factor from grams to moles.  That's published, or written on the bottle, just like the density is.  Or you can calculate it, from elemental mass.