Help me I need help on Chemistry!!!

[Riskhk]

A 0.2560 g of sample of an Al-Zn alloy reacts with HCl to form hydrogen gas:
Al(s) + 3H+ --> Al3+ + 3/2 H2(g)
Zn(s) + 2H+ --> Zn2+ + H2(g)

The hydrogen produced has a volume of 0.158 L of 25 degree C and 1.00 atm. What is the mass percent of Aluminum in the alloy?

Its worth a try ..... thanx

 

[Francodman]

god, lemme break out the chem notes ....




SIKE! schoo's over son!

 

[Mday]

wow, must be some advanced chemistry. you are dealing with bolumes of hydrogen.

 

[Mday]

you have to use algebra here...

say the alloy has x moles of Al per y moles of Zn, the formula being AlxZny. This is for the entire sample, imagine the sample (as written on paper) as one big molecule .

So, the big molecule has a mass of 0.2560 grams. Now, x is the amount of moles of Al, so x times the molar mass of Al is the mass of Al in that big molecule. y times the molar mass of Zn is the mass of the Zn in that big molecule. and mass of Al + mass of Zn = 0.2560 grams. This gives you ONE equation with respect to both x and y

Since you now have x moles of Al, you now need 3x moles of H+ ions for the first equation. And for Zn, you need 2y moles of H+ ions. This means on the RIGHT hand side of the equation, you need 1.5x moles of H2 gas for the first chemical equation, and y moles of H2 gas for the second.

remember that at STP, one mole of a gas takes up 1 L of space. so since you are at STP, there are 0.158 moles of H2 gas. This means:
1.5x + y = 0.007049166

Now you have ANOTHER equation involving x and y.

So, you have a system of 2 equations with 2 unknowns. Do some alegra, and solve for x and y. Since you are looking for % mass of Al and x times the molar mass of Al gives you the mass of Al, the mass of Al divided the mass of the big molecule (remember, this is what we are calling the sample) gives you the decimal form of the %. multiply now by 100 to get the %.

<<corrected>>

 

[flood]

(((mass of one molecule of Al-Zn)g/(.2560g))(mass of Al))/(.2560)
I think...

 

[Riskhk]

thanx mday...damn how do you all that

 

[Mday]

i am not stupid.

and if you can do the problem, neither are you.
--

what do you mean? do you not understand the response, or what?

 

[Riskhk]

duh ...i m dumb

 

[Francodman]

ahh, the great stoichiometry!

 

[Mday]

no, i am dumb.

22.414 L per mol , forgot the conversion factor...

 

[Riskhk]

nm have to convert 1.5 litter to mol?

 

[Mday]

the second equation with x and y should be: 1.5x + y = (.158L divided by 22.414 L\mole) = 0.007049166...

 

[Mday]

i am getting like 30%.

 

[Riskhk]

THANK YOU THANK YOU THANK YOU.......finally got the molar ratio
x = 0.00288234707 30.38%
y = 0.0027256454 69.62%

 

[Mday]

what's this for anyway? i know it's for chemistry.

college, high school, summer?

HW? it better NOT be a take home test.

 

[Riskhk]

extra credit for college chemistry...hehe due in 6 hours thanx alot...please dont tell me you're a 6th grader or something

 

[Capn]

I hope this an intro class

 

[Mday]

it better be an intro class.

 

[Androck99]

EXTRA CREDIT IN COLLEGE!?!?!?! What school are you at? Damn...I wish I could've gotten some extra credit in some of my classes at Oregon State...oh well, 3.4 cum isn't too bad for an EE...

 

[Riskhk]

it is an intro class... it sucks when you take chemistry after not taking it for 3 years...everything is new