Answer:
C₄H₈O₄ is the molecular formula of the solid.
Explanation:
Let's apply the freezing point depression to solve this:
ΔT = Kf . m
where Δt = Freezing T° pure solvent - Freezing T° of solution
Kf, the cryoscopic constant
m = molalilty, moles of solute in 1kg of solvent.
We must determine the molecular weight to know the molecular formula of the solid
Let's replace the data.
1.6°C = 8 °C/m . m
We can determine molality, by this:
1.6 °C / 8°C/m = 0.2 m
mol of solute / 1kg of solvent = 0.2
Let's convert the mass of solvent from g to kg, to determine the moles of solute.
mol of solute / 0.0281 kg = 0.2 mol/kg
28.1 g . 1kg / 1000 g = 0.0281 kg
mol of solute = 0.0281 kg . 0.2 mol/kg → 0.00562 moles
Molar mass (g/mol) → 0.673 g / 0.00562 mol = 120 g/mol
Now, we can apply the percent composition.
100 g of compound have ___ 40 g C ___6.7 g H ___ 53.3 g O
120 g of compound must have:
(120 . 40) / 100 = 48 g of C
(120 . 6.7) / 100 = 8 g of H
(120 . 53.3) / 100 = 64 g of O
Let's convert the mass of each elements to moles
48 g . 1 mol/12 g = 4 C
8 g . 1 mol /1g = 8 H
64 g . 1 mol / 16g = 4 O
