Calculating the Number of Gas Molecules in an Excellent Laboratory Vacuum

[noname1]

An excellent laboratory vacuum has a pressure of 4.00x10^-18 atm, or 4.04x10^-13 Pa. How many gas molecules are there per cubic centimeter in such a vacuum at 297 K?

n/v = p/rt


n/v = 4.04x10^-13 / (8.31x297) = 1.66x10^-16 mol/m³

1.66x10^-16 mol/m³ * (1/100cm)³ = 1.66x10^-22 mol/cm³

but something is wrong, please verify and she what i am doing wrong

 

[rock.freak667]

1 mole contains how many molecules?

 

[noname1]

1 mole contains how many molecules?

6.022x10^23

 

[rock.freak667]

6.22x10^23

And you have 1.66x10^-22 moles, so how many molecules do you have?


Actually now that I see it, you are finding per cm³.

R has the units J/mol.K

J = 1 Pa m³, so you'll need to change your units for R for it to work out properly.

 

[noname1]

ok i see it now i forgot to multiply by (6.022x10^23/mol)

i only got 1 more try at answering this question :(

(1.66x10^-16 mol/m³) * (m/100cm)³ * (6.022x10^23/mol) = 99.97 molecules/cm³

am i correct now?