Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: DessaM on November 26, 2012, 03:34:38 AM
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I'm trying to figure out how to set up this equation. Each time I seem to be getting the wrong answer.
Zinc reacts with aqueous sulfuric acid to form H gas: Zn + H2SO4 -----> ZnSO4 + H2
What mass of Zinc is necessary to make 24.9L of hydrogen gas at 1.44atm and 508.15K ?
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Show how you get the wrong answer, we will start from there.
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Show how you get the wrong answer, we will start from there.
This is how I had set it up the first time
22.4 L H2 * (1 mol H2/ 352.88 L H2) * (1 mol Zn/ 1 mol H2) * (65.39g Zn/ 1 mol Zn) = 4.614 g Zn
I know the (1 mol H2/ 352.88 L H2) is incorrect. That's where I'm having the most difficulty is how to set up equations that don't involve STP.
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Show how you get the wrong answer, we will start from there.
This is how I had set it up the first time
22.4 L H2 * (1 mol H2/ 352.88 L H2) * (1 mol Zn/ 1 mol H2) * (65.39g Zn/ 1 mol Zn) = 4.614 g Zn
I know the (1 mol H2/ 352.88 L H2) is incorrect. That's where I'm having the most difficulty is how to set up equations that don't involve STP.
Where has the 352.88 figure come from?
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Show how you get the wrong answer, we will start from there.
This is how I had set it up the first time
22.4 L H2 * (1 mol H2/ 352.88 L H2) * (1 mol Zn/ 1 mol H2) * (65.39g Zn/ 1 mol Zn) = 4.614 g Zn
I know the (1 mol H2/ 352.88 L H2) is incorrect. That's where I'm having the most difficulty is how to set up equations that don't involve STP.
Where has the 352.88 figure come from?
I got that from v=t/p (which I know is incorrect) I just did v=508.15 / 1.44atm = 352.88 My teacher just crossed it out on my worksheet and hasn't shown me the correct way yet..
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The equation you need is the ideal gas law PV = nRT http://en.wikipedia.org/wiki/Ideal_gas_law
You have tried to use a bit of the equation (v=t/p) but it only works if you use the full equation.
You need to pick the right value of R (http://en.wikipedia.org/wiki/Ideal_gas_constant) for the units you have been given for P, V and T and solve for n.
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The equation you need is the ideal gas law PV = nRT http://en.wikipedia.org/wiki/Ideal_gas_law
You have tried to use a bit of the equation (v=t/p) but it only works if you use the full equation.
You need to pick the right value of R (http://en.wikipedia.org/wiki/Ideal_gas_constant) for the units you have been given for P, V and T and solve for n.
Okay so I applied the idea gas law using n=PV/RT so I got .859 mol H2
Then I did this:
.859 mol H2 * (1 mol Zn / 1 mol H2) * (65.39 g Zn / 1 mol Zn) = 56.17g Zn
Is that the correct way to set up the equation? And am I using the mol ratios correctly?
Thank you for your *delete me*
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The equation you need is the ideal gas law PV = nRT http://en.wikipedia.org/wiki/Ideal_gas_law
You have tried to use a bit of the equation (v=t/p) but it only works if you use the full equation.
You need to pick the right value of R (http://en.wikipedia.org/wiki/Ideal_gas_constant) for the units you have been given for P, V and T and solve for n.
Okay so I applied the idea gas law using n=PV/RT so I got .859 mol H2
Then I did this:
.859 mol H2 * (1 mol Zn / 1 mol H2) * (65.39 g Zn / 1 mol Zn) = 56.17g Zn
Is that the correct way to set up the equation? And am I using the mol ratios correctly?
Thank you for your *delete me*
I'm getting the same answer. So either we are both right or both wrong. :)
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Watch out for rounding up part way through I get 0.8599... moles of hydrogen coming from 56.23g of Zinc.