Question

How many molecules of co2 gas are present in the sample

Answer 1

if its simply co2 then there 3 molecules

Answer 2

Use ideal gas law to determine how many moles of air: 
Note, convert T (31*C) into K; and use value of R which has units L atm/ mol * K 


PV = nRT 
(1.00)(1L) = n(0.08205746)(304) 
n = 0.0401 moles 
To convert moles to number of molecules, multiply by 6.02 x 10^23 

So number of moles of each converted to molecules: 
N2: (0.7808)(0.0401)(6.02 x 10^23) = 1.88 x 10^22 molecules 
O2 = (0.2094)(0.0401)(6.02 x 10^23) = 5.05 x 10^21 molecules 
CO2 = (0.0005)(0.0401)(6.02 x 10^23) =1.21 x 10^19 molecules 
Ar = (0.00930)(0.0401)(6.02 x 10^23) = 2.25 x 10^20 molecules