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April 30, 2016

# Homework Help: science

Posted by josh on Saturday, August 27, 2011 at 6:31am.

1. What weight of aluminum may be obtain from 1 kg of aluminum oxide?
2. how many liters of hydrogen would be form by the reaction of 25g of hydrochloric acid and sufficient quantity of zinc?
3. 0.82l of an unknown gas at 35 degree Celsius and 80 cm-Hg weigh 2.46g. compute for the molecular weight of the unknown gas?
• science - drwls, Saturday, August 27, 2011 at 7:18am

1.) The chemical formula of aluminum oxide is Al2O3. The total mass per mole is
27 + 3*16 = 75 g. Of that mass, 27 g is aluminum atoms. Therefore 27/75 or 36.0% of the mass is aluminum.

The answer is therefore 36% of 1000 g. How much is that?

2.) First, let's write down the chemical reaction.
Zn + 2 HCl -> ZnCl2 + H2

25 g of HCl is 25/36.5 = 0.685 moles.
that will form, wityh excess Zn, half as many moles of H2. Convert that to gas volume assuming STP conditions.

3. 80 cm Hg is the PRESSURE, and that equals = 0.1053 atm. At 35 deg C (which is T = 308 K) the number of moles in 0.82 L would be given by
n = PV/RT = (0.1053*0.82)/(0.08206*308) = 3.42*10^-3 moles

If that is 26 g, the mass of one mole is 7600 g

That is a very large molecular mass. Are you sure all of your numbers are correct?