Question

Use of the Data Booklet is relevant to this question.

The approximate percentage composition of the atmosphere on four different planets is given in
the table below.

The density of a gas may be defined as the mass of 1 dm3
of the gas measured at s.t.p.

Which mixture of gases has the greatest density?

planet major gases /
% by number of molecules
A Jupiter H2 89.8, He 10.2
B Neptune H2
80.0, He 19.0, CH4 1.0
C Saturn H2 96.3, He 3.25, CH4 0.45
D Uranus H2 82.5, He 15.2, CH4 2.3

Answer 1

Calculate the density for all the gases, assume that you have 1 L and use the molar masses of the gases, for example:

For Uranus, the composition is 82.5% is \(H_2\) and 15.2% is He, 2.3% \(CH_4\)

so the mass in 1 L \(= 82.5\%M_{H_2}+ 15.2\% M_{He}+2.3\%M_{CH_4}\)

\(= 0.825(2g/mol)+ 0.152(2g/mol)+0.023(16g/mol)\)

=2.322 g


The density is the same because were using 1 L, if you need to show the work, then:

\(\rho_{Uranus}=\dfrac{2.322g}{1L}=2.322~g/L\)



(i'm assuming the percent composition by volume by way).

Answer 2

how is helium 2g/mol if helium must have 4g/mol

Answer 3

oh damn, sorry, i made a mistake.

Answer 4

its okay but how did you reach to the number 2.322 did you divide the percentage by its mass

Answer 5

multiplied the percentage of each gas by it's molar mass

Answer 6

so it should be \(\rho_{Uranus}=2.626 ~g/L\)

Answer 7

thank you so much ::) :D

Answer 8

no problem! (thats not the final answer though)

Answer 9

i know the idea know

Answer 10

and i can solve the rest

Answer 11

good stuff, i was just making sure.