Answer:
The molecular formula for the organic compound is C₈H₈O₂
Explanation:
70.58 % C , 5.9 % H , and 23.50 % O
This is a percent by mass, so:
in 100 g of compound I have 70.58 g of C, 5.9 g of H and 23.5 g of O.
We need to apply the formula for freezing point depression, the colligative property.
ΔT = Kf . m
Where ΔT means T°F (pure solvent) − T°F (solution)
Kf, the cryoscopic constant and m is molality (mol of solute in 1kg of solvent); Kf for cyclohexane is 20.8 °C/m
6.59°C - 3.29°C = 20.8 °C/m . m
3.3°C = 20.8 °C/m . m
3.3°C /20.8 m/°C = molal
0.158 m/kg
In 1kg of solvent I have 0.158 moles, but I have 718.1 g of cyclohexane
1000 g _____ 0.158 moles of solute
718.1 g _____ 0.114 moles of solute
To find out the molar mass of my compound I have to divide
mass/mol → 15.5 g /0.114 m = 136.04 g/m
Now I have to work with the percent and think this rules of three:
100 g of compound has ____ 70.58 g of C __5.9 g of H __23.5 g of O
136.04 g of compound has ___ 96.02 g of C __8.02 g of H __ 32 g of O
Molar mass of C = 12 g/m
Molar mass of H = 1 g/m
Molar mass of O = 16 g/m
g / molar mass = moles
C: 96 g / 12 g/m = 8
H: 8 g / 1 g/m =8
O: 32 g/ 16 g/m = 2
The molecular formula for the organic compound is C₈H₈O₂
