1)According to the Dalton’s Law the total pressure is the sum of the partial pressures thus
p=pC3H8+pCH4=0.395[atm]+0.485[atm]=0.88[atm] 2)The partial pressure of the i-th component can be found as (it follows from the ideal gas law) as product of the mole fraction and total pressure
pi=ωip
thus the mole fraction of C3H8 is
ωC3H8=ppC3H8=0.88[atm]0.395[atm]≈0.449 3)We can find the number of moles of C3H8 using the ideal gas law for it
pC3H8V=νC3H8RTthus
νC3H8=RTpC3H8V and we can do calculations
νC3H8=8.314[K⋅molJ]⋅(30+273.15)[K]0.395⋅101325[Pa]⋅2.95⋅10−3[m3]≈0.0468[mol] 4)We can calculate the number of moles of CH4 using the same way
νCH4=8.314[K⋅molJ]⋅(30+273.15)[K]0.395⋅101325[Pa]⋅2.95⋅10−3[m3]≈0.0575[mol] and then calculate the mass of the sample
m=νC3H8MC3H8+νCH4MCH4
m=0.0468[mol]⋅44.097[molg]+0.0575[mol]⋅16.043[molg]=2.986[g]
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