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Old 12-01-2009, 07:33 PM   #1
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Default Chemistry Question

The volume of hydrogen gas at 38.0°C and 763 torr that can be produced by the reaction of 4.33 g of zinc with excess sulfuric acid is __________ L.


Any idea? It's not at STP, so I don't know... What I got is
4.33/65.39 = .066 = moles of zinc.
The mole ratio of H2 to Zinc in the reaction is 1:1, so there is .066 moles of hydrogen. And at STP, 1 mole of gas occupies 22.4 L. But it's not at STP... so idk...

I think I may have figured it out... PV=nRT...
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Old 12-01-2009, 08:09 PM   #2
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Default Re: Chemistry Question

Like you've state there, you need to use PV = nRT.

You're given pressure and temperature. You know what the gas constant is. All you need to do is figure out moles. Since you're given the reaction (I assume) and the initial mass of Zn you're able to find out the mole ratio between Zn and H2. Since you've already figured out moles of H2, all you have to do is plug and chug.
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Old 12-01-2009, 08:52 PM   #3
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Default Re: Chemistry Question

I had to look up the equation... This is only a practice test, the actual test they will usually give it too you. But yeah, I think I got that one right. Still plenty I didn't get right though... lol

1. An 8.29 g sample of calcium carbonate [CaCO3 (s)] absorbs 50.3 J of heat, upon which the temperature of the sample increases from 21.1°C to 28.5°C. What is the specific heat of calcium carbonate?

2. Sodium hydride reacts with excess water to produce aqueous sodium hydroxide and hydrogen gas:



A sample of NaH weighing __________ g will produce 982 mL of gas at 28.0°C and 765 torr, when the hydrogen is collected over water. The vapor pressure of water at this temperature is 28 torr.

3. Which type of bonding does Mg form upon solidification?

4. Determine the temperature required (in Kelvin) to change the vapor pressure of a system from 9.40 atm at 423.0 kelvin to 31.30 atm if the enthalpy of vaporization is 50.2 kJ/mol.

5. Diethyl ether is a volatile organic compound. The vapor pressure of diethyl ether is 401 mm Hg at 18°C and theHvap = 26.0 kJ/mol. Calculate the vapor pressure of diethyl ether at 25°C.

Got any ideas on any of those?...
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Old 12-01-2009, 10:29 PM   #4
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Default Re: Chemistry Question

1. Heat = Specific Heat * Change in Temperature * Mass

2. I couldn't see the picture, but I think it's PV = nRT again.

3. Does it mean with other elements? In that case I'd say ionic.

4. http://en.wikipedia.org/wiki/Vapor_pressure. I can't quite remember this one so that might help.

5. This one will use the same equation as 4. This equation may also be applied at 2.

**I'm not sure if the equation in the link is the one you need to be using. I'll look into it later as I need to eat dinner.
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Old 12-01-2009, 10:39 PM   #5
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Default Re: Chemistry Question

Ok, thanks man, yeah, we use a similar equation I think...

Was gonna rep you, but it wouldn't let me... I'll get you later I guess, lol.
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