Answer:
molecular formula of liquid = C₈H₁₈
Explanation:
First we determine the empirical formula of the liquid:
Number of moles of each element present in the liquid = % mass / molar mass
For Carbon, (molar mass = 12.01 g/mol) : 84.2/12.01 =7.011 moles
For Hydrogen (molar mass = 1.01 g/mol) : 15.8/1.01 = 15.643
Simplest mole ratio of the elements, C : H is given by:
C = 7.011/7.011 = 1.0
H = 15.643/7.011 = 2.23
Multiplying through with 5, C:H = 5:11
Therefore, empirical formula is C₅H₁₁
The molecular mass of the liquid is next determined:
Using PV = nRT to find the number of moles of the liquid present
P = 5.0 atm; V = 568.0 mL = 0.568 L; R = 0.082 L*atmmol⁻¹ K⁻¹; T = 273 + 120 = 393 K
n = PV/RT = (5*0.568)/0.082*393
n = 0.088 moles
Molar mass of liquid = mass/no of moles = 10.0 g/ 0.088 moles = 113.63 gmol⁻¹
Molecular formula = n(empirical formula)
Molar mass of empirical formula, C₅H₁₁ = 71 gmol⁻¹
n = molecular mass/empirical mass = 113.63/71 = 1.6
Therefore, molecular formula = 1.6*(C₅H₁₁) = C₈H₁₈
