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Topic: Gas Laws problems help.  (Read 5741 times)

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Offline dmbocci

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Gas Laws problems help.
« on: November 24, 2008, 08:07:28 PM »
Some questions out of a larger group I had that I am having trouble getting started with. Some I have worked some answers, but they dont seem right. If anyone wants to work them, go for it, if not, try to point me in the right directions, equations to start with or steps.
Thank you ahead of time.

1. Calculate the density of water vapor at 110 deg C and 99 kpa.

2. A compound with the empirical formula BH3 was found to have a vapor density of 1.24 g/L at STP. Determine the molecular weight AND the molecular formula of this gas.

3. Consider the reaction of solid copper(I) sulfide with oxygen gas to produce solid copper(I) oxide and gaseous sulfur dioxide.
A.write the balanced chemical equation for this process.
B. What volume of oxygen gas, measured at 27.5 deg C and 0.998 atm, is required to react with 25g of copper(I) sulfide?

4. A sample of solid potassium chlorate is decomposed, forming solid potassium chloride and gaseous oxygen. The oxygen produced was collected by the displacement of water at 22deg C at a total pressure of 754torr. The volume of the gas collected was 0.65L, and the vapor pressure of water at 22deg C is 21torr.
A. Write the balanced chemical equation.
B. Determine teh mass of potassium chlorate in the sample that was decomposed.

5. Calculate the root-mean square speed for:
A. a xenon atom at 298k.
B. an oxygen molecule at 298k.

6. Both hydrogen and helium have been used as buoyant gases in blimps. If a small leak were to occur in a blimp filled with both gases, which gas would effuse more rapidly and by what factor?

7. A gas of unknown molecular mass was allowed to effuse through a small opening under constant pressure conditions. It required 72 s for the gas to effuse. Under identical experimental conditions, it required 28s for the 02 gas to effuse. Determine the molar mass of the unknown gas.

8. Calculate the pressure exerted by 50.0g CO(g) in a 1.00L container at 25deg C by:
A. Using the ideal gas law, and
B. Using the van der walls equation.
C. Compare the results from part A and B. Does CO(g) behave ideally under these conditions?
(useful info: For CO, a=1.49atm Lsquared/molsquared and b=0.0399L/mol.)

Offline Tyler Durden

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Re: Gas Laws problems help.
« Reply #1 on: November 24, 2008, 09:40:45 PM »
1) Use the formula d=PM/RT for number 1. Where d=desnsity, P=pressure, M=molar mass, R=gas constant, T=temperature. Make sure you use the correct gas constant. 8.3145 for when using kPa i believe.

2) Use the same formula, d=PM/RT, to find the molar mass. Once you have the molar mass you can calculate the molecular formula with ease.

3) Balance the equation. Once the equation is balanced find the amount of oxygen gas in moles that was needed to react with the 25g of Cu. Once you get the moles of oxygen, simply find the volume using the Ideal Gas Equation. PV=nRT

4) Its similiar as question 3, its just the other way around. Find the amount of oxygen that was released (remember to find the correct pressure for oxygen gas by taking into account that vapor was present), then use stoichimoetry to find how much potassium chlorate there was from the amount of oxygen gas you calculated.

Offline Borek

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Re: Gas Laws problems help.
« Reply #2 on: November 25, 2008, 03:42:38 AM »
1) Use the formula d=PM/RT for number 1.

Note where does the formula come from. It is not yet another fomula to remember - it is just a clever use of what you should already know. Density is mass/volume, right? Mass and number of moles are linked through the molar mass, number of moles and volume are linked by the ideal gas equation - just combine these two equations.
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