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April 18, 2014

Homework Help: Chemistry Check if its right XD

Posted by becky on Tuesday, January 9, 2007 at 10:31pm.

Ok here is the problem but i only need help on part a XD i think i did it wrong..so can you check my work? and tell me where i made the mistake?

The space shuttle uses aluminum metal and ammonium perchlorate, NH4ClO4, in tis reusable booster rocket. The products are aluminum oxide, aluminum chloride and NO and steam. The reaction mixture contains 5.75grams of AL and 7.32grams of NH4ClO4.

a) what is the theoretical yield of aluminum chloride? Note: not all of the chloride comes from NH4ClO4

i got an equation of this

3Al+3NH4ClO4-->Al2O3+AlCl3+3NO+6H2O

is that correct first of all?

and then i did..

mol AL=5.75g*(1mol/26.98g)=.2131 mol

mol NH4ClO4=7.32grams*(1mol/117.5g)=.06229 mol

and then i did

.06229(1mol/3mole)=.012mol AlCl3

did i do it right? and does it end up like that..if not please tell me what i did wrong or explain

thanks


Question 1. If all of the Cl does not come from NH4ClO4, then where does it come from? The only source of Cl you have is in NH4ClO4 AND the only product you have containing Cl is AlCl3. Is there something else we are supposed to add to the NH4ClO4?

I am not sure cause it said the Note thingy on the problem..so im not even sure myself XD that is why im not sure about my solution

ok.
Assuming the products are correct, your equation balances. I used 117.49 for molar mass of NH4ClO4, 26.98 for molar mass Al.

mols NH4ClO4 = 0.06230 which is essentially the same as you have.

mols Al = 5.75/26.98 = 0.2131. However, since the ratio is 3 mols NH4ClO4 to 3 mols Al, the oxidizer to fuel ratio (Al is the fuel) is 1:1 so there is an excess of Al present. That means we must use the NH4ClO4 to calculate the theoretical mols AlCl3.
mols AlCl3 = mols NH4ClO4 x (1 mol AlCl3/3 mols NH4ClO4) = 0.02077 mols AlCl3.

grams AlCl3 = mols AlCl3 x molar mass AlCl3 = 0.02077 x 133.33 = 2.77 grams AlCl3 = theoretical yield.

I think you were ok down to
0.06229/3 = ?? but you must have punched in the wrong number because the answer is 0.02077 (or 0.02076 using your values) and not 0.012. Then you would have multiplied that by the molar mass of AlCl3 to obtain the theoretical yield.
I hope this helps.
Just for the fun of it I went to www.google.com and typed in NH4ClO4 space shuttle and that site (I don't know if it is a very good one or not) gave the products as
Al2O3
AlCl3
N2 (instead of NO)
H2O.
Of course that changes the balancing part and the answer. BUT you should go with the problems products. I still don't understand the note.

ohh i think i get it..hmm for the note thingy i think imma go ask my teacher about it

thanks though ^^

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