Homework Help: Chem (Help!)

Posted by Lisa on Monday, April 28, 2008 at 5:25pm.

I really need help answering these questions.

A sample of CO2 gas with a mass of 0.30 g is placed in a 250 mL container at 400 K. What is the pressure in atmospheres exerted by this gas?

Before you can put the numbers into an equation and solve for the volume, change the mass to moles by using the following equation:

1)mass*molar mass

2)mass/molar mass

3)mass*(6.02 x 10²³)mass/

4)mass(6.02 x 10²³).

If you calculate the molar mass of CO2, what do your get? g/mol (round the atomic masses to hundredths place and your answer should also be rounded to the hundredths place)

Now, use the equation you chose above to calculate the moles of CO2. mol(round to the ten thousandths place)

Almost ready to calculate our answer, but first we need to convert the mL to L.
250 mL x 1)1000L/mL 2)1L/1000mL 3)100L/ mL 4)1L/100mL = our answer in L.

After plugging your data into the correct ideal gas law equation, you get LatmpsimL (round to the hundredths place).

Chem (Help!) - DrBob222, Monday, April 28, 2008 at 5:48pm
You want to use PV = nRT
It appears that someone has set up the problem to work it step by step. Can you not follow those steps? Has someone tried to help and now you're stuck. Are these instructions from your teacher? I can help you through it but I need to know the answers to the above questions before I start. Thanks for using Jiskha.
Chem (Help!) - Lisa, Monday, April 28, 2008 at 5:53pm
Yes the instructions were from my teacher.
Chem (Help!) - DrBob222, Monday, April 28, 2008 at 6:09pm
Are you sure you copied the instructions correctly? Some of them don't make sense to me.
I have copied the question to this space.
A sample of CO2 gas with a mass of 0.30 g is placed in a 250 mL container at 400 K. What is the pressure in atmospheres exerted by this gas?

Here is how you do the problem.
Use PV = nRT, the general gas equation.
P is pressure in atmospheres. Solve for this. That is the only unknown in the equation. The answer will be in the unit atmospheres.

V = volume in liters. The problem gives 250 mL so change that to 0.250 L.

n = number of mols of gas. The problem gives 0.30 grams. mols = grams/molar mass = 0.30/44 = ?? (I have estimated the molar mass of CO2. You should confirm that number.)

R is the universal gas constant, which for this problem is 0.08206 L*atm/mol*K.

T is the temperature in Kelvin which the problem lists as 400 K.
Now, just plug those numbers in and solve for P. I'll be happy to check your answer.

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