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Topic: Analysis of An Al-Zn Alloy  (Read 3840 times)

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Offline meowmor.3

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Analysis of An Al-Zn Alloy
« on: October 26, 2017, 09:44:49 PM »
What volume(mL) of Hydrogen gas, saturated with water vapor, will be obtained from a .1138g sample of alloy which is 73.2% Al? (Pbar=754.3,T=21.2C)

I am not sure what to do with the % of Al and the mass of the alloy.

I am using PV=nRT to try to solve this problem.

P= 754.3-18.7=735.6mmHg/760mmHg=.9678 atm
V=?mL ( what I am looking for)
n=( not sure how to figure out n)
R= constant #
T= 21.2+273.15=294.25K

Offline Borek

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Re: Analysis of An Al-Zn Alloy
« Reply #1 on: October 27, 2017, 03:05:29 AM »
Apparently they want you to calculate mass of Al and follow the stoichiometry.

If that's the whole question it is rather poorly formulated, as it doesn't say anything about the other 26.8% of the alloy, nor does it say what reaction is responsible for hydrogen production. I can only guess you are expected to assume hydrogen will be produced only in the reaction of Al with water (or some acid).
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Offline Enthalpy

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Re: Analysis of An Al-Zn Alloy
« Reply #2 on: October 27, 2017, 07:11:47 AM »
If the rest of the alloy is Zn as the title hints, then it's very uncommon, because the solubility of Zn in Al is far less. Common Al-Zn have 5% Zn, very few ones 8%, plus pepper and onion.

I used the extra-hard RSA-708 alloy with 9.5% Zn. It is made by instant solidification of liquid droplets on a cold spinning drum, after which the obtained flakes are sintered together, so Zn has no opportunity to separate. Standard alloying in the melting pot wouldn't allow that proportion.

I've never seen an Al alloy with more Zn than 9.5%, and strongly suppose that alloys with 27% don't exist.


Missing information here, like "reacting with an acid"? Then you'd write the reactions with Al and with Zn, deduce the moles of H2 from the moles of Al and Zn, and compute the volume at the give pressure.

Are 754.3 mmHg? Then H2 behaves nicely like a perfect gas. If they are bar, not at all.

Don't forget neither the difference between atm and bar, if you're supposed to compute with four places. In fact, even the perfect gas law is more than 100ppm wrong with H2 under these conditions.

Offline Arkcon

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Re: Analysis of An Al-Zn Alloy
« Reply #3 on: October 27, 2017, 07:46:45 AM »
Well then, Enthalpy:, this is yet another example of a teacher or text book writer ignoring highly technical aspects when coming up with a problem for students to solve.  This comes up from time to time, and is always funny.  I don't believe it invalidates an opportunity to see a student work out a problem.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

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