[Mr.2007]

The question is

What is the mass, in grams, of 125mL of CO₂ at STP

[Borek]

pV=nRT

Google ideal gas volume at STP

[Mr.2007]

^^^ can you be more specific like what steps i need to go through because im completely lost

[Borek]

volume -> number of moles -> mass

1 mole of ideal gas at STP has always the same volume - you will find this value with Google in no time.

[Mr.2007]

i found that 1 mole of an ideal gas at stp is 22.4L what do i do next

[enahs]

i found that 1 mole of an ideal gas at stp is 22.4L what do i do next

Nothing. Borek was drunk.

In the Ideal Gas Law (http://en.wikipedia.org/wiki/Ideal_gas_law)
PV=nRT

You know P (pressure), V (volume), R (gas constant) and T (temperature)
The Pressure and Temperature come from the fact that it is given at STP (Standard Temperature and Pressure).

Solve for n (number of moles) and then convert from moles to grams.

You just have to get your units correct, and make sure to use the appropriate gas constant for those units, when solving for n.

[Borek]

i found that 1 mole of an ideal gas at stp is 22.4L what do i do next

You have 125 mL (or 0.125 L) of gas, and you know 1 mole occupies 22.4 L. Can you calculate number of moles of gas from these data?

[Mr.2007]

i found that 1 mole of an ideal gas at stp is 22.4L what do i do next

Nothing. Borek was drunk.

In the Ideal Gas Law (http://en.wikipedia.org/wiki/Ideal_gas_law)
PV=nRT

You know P (pressure), V (volume), R (gas constant) and T (temperature)
The Pressure and Temperature come from the fact that it is given at STP (Standard Temperature and Pressure).

Solve for n (number of moles) and then convert from moles to grams.

You just have to get your units correct, and make sure to use the appropriate gas constant for those units, when solving for n.

ok how do i solve for n

[Mr.2007]

do i use

P * V / R* T = n

[enahs]

ok how do i solve for n

Basic algebra.

PV = nRT

If you divide both sides by RT, you get

PV = n
RT


You actually could work it borkes way with ratios, as well. But since you clearly need algebra practice, I would work it this way!

http://www.intmath.com/Basic-algebra/Basic-algebra-intro.php
http://library.thinkquest.org/20991/prealg/eq.html
http://www.mathleague.com/help/algebra/algebra.htm

*edit*

do i use

P * V / R* T = n

Yes. You submitted that post while I was typing mine!

[Mr.2007]

were do i get R from is it 0.0821

[Mr.2007]

and for volume do i use

125mL or 0.125L

[Yggdrasil]

In general, for ideal gas law problems you will use R = 0.0821 L*atm/mol*K.  If you use this form, then your volume must be in L, your pressure must be in atm, and your temperature must be in K for the units to cancel correctly.

[Mr.2007]

ok so i did

1 atm * 0.125 L
_____________        = 415.9
0.0821 * 273.15 K

so now do i convert 415.9 mol to grams

[Borek]

If 1 mole occupies 22.4 L, is it possible that 0.125 L of gas is over 400 moles? Or should it be just a fraction of mole?