CHEMISTRY QUESTION! i need help, what is this question asking?

Question

A student COLLECTS a 2.30 dm^3 sample of CO2 with a pressure of 92.7kPa and temperature of 17.0 degree Celcius. if he wants to determine the number of molecules of CO2 that his sample contains, what would he need to do.

Is it trying to say convert 2.30 dm^3 CO2 into molecules? the reason i came to this conclusion is because the question is asking "how many molecules of CO2 does his sample contain" and the information provided says that he COLLECTS 2.30 dm^3 sample of CO2

but my book does something completely different

it finds V2 (2 is a subscript) using the combined gas formula

and then finds the amount of molecules for CO2 for the second volume

Answer 1

if you can find out the number of moles of gas, you can find the # of atoms (using Avogadro's number = 6.0221415 × 10^23 atoms per mole).

Use Ideal Gas Law (PV=nRT) to find n, which is the number of moles. R is a constant (0.082054 liter*atm /degree*mole, I believe, but verify in your text book).

P is pressure

V is volume (2.3 dm, convert to liters)

T is temperature in Kelvin, so convert from C.

answer: (6.022 * 10^ 23) * n atoms

n = pv/rt = 92700 * 2.3 / (0.0821 *  290)  = 8955 moles

answer = 5.40 * 10^27

that seems a little heavy, however, so double check.

Answer 2

your book may be using a very old fashioned way; finding the volume at the so-called STP (which I have never seen used outside the high school classroom), and comparing that with 22.4 L = 1 mole at STP to get the number of moles.

Timothy's way of doing it is much better.  Remember, of course, to use degrees Kelvin, and 1 dm^3 = 1 L.