[chemhuff]

Hi...well, I sincerely say that I am NOT using this forum to get answers!  I've tried these problems a million times and can't understand them!  I know how to get the limiting reactant, its just the questions really confuse me!!

1. I already balanced the equation:
Fe₃O₄ + 4H₂ ---> 3Fe + 4H₂O
Now here's the question: For the equation above, where 11.5g magnetic iron oxide is combined with .450 hydrogen gas, which substance is the limiting reactant?

I'M DUMBFOUNDED!!!!
Here's the last one: (equation already balanced)
For the unbalance equation below, what mass of solid AgCl will precipitate from a solution of 1.50g CaCl₂ with excess AgNO₃?
CaCl₂ + Ag NO₃ ---> AgCl + Ca(NO₃)₂
PLEASE!  I SINCERELY ASK FOR *delete me*!  ...why do they have to make these questions confusing...urr

[Mitch]

Tell me how many moles of Iron Oxide you have. Then tell me how many moles of Hydrogen you have.

[chemhuff]

ok...forgive me if its wrong...i suck at this...for iron oxide, 27.82 mol (?) and for hydrogen 1.3 mol (?)  
I multiplied the atomic mass w/the number of atoms then divided it by one mole...is that wrong?

[Mitch]

Lets look at your units.

Atomic weight = grams / mol

# of atoms = (atoms)

moles = moles.

Now this is what you did, you multiplied (grams/mol) and (# of atoms) = grams*#atoms/moles

Then you divided by moles, so the units of that is = grams*#atoms/moles²

That doesn't give you the units of moles, try again.

[chemhuff]

ok....urr....is the mol for iron oxide 42.15?  and the mol for hydrogen 48.176?  1st, for iron oxide, I multiplied 3 atoms of iron times mole, then 4 atoms of oxygen times mole, and got a total of 42.15 mol for iron oxide.  Then I did the same for Hydrogen, 8 atoms*mole....GOD...i think i got it wrong again...

[chemhuff]

NO WAIT!!  I think I got it this time....number of moles for iron oxide is 18.26, and number of moles for hydrogen is 1.32?

[Mitch]

moles of H₂ is 0.225.

[chemhuff]

oh, ok...i calculated it wrong...sorry, I had to review the mole concept...so what do I do now?

[Mitch]

How many moles of Iron oxide do you have?

[chemhuff]

i said 18.26.....thats wrong?

[chemhuff]

I got the answer!! With the help of Tiger....she amazingly tolerated my stupidity in Chemistry ...the answer for the 1st question is Fe304!!  I'm still working on the second question!!

[Mitch]

Tiger should help you out on the board, so all can benefit.

[Donaldson Tan]

CaCl2 + 2AgNO3 -> 2AgCl + Ca(NO3)2

given excess silver nitrate added, you can safely assume all the chloride ions present is precipitated out as silver chloride.