A compound has the empirical formula CH2O. When 0.0866 g is dissolved in 1.0 g of ether, the solution’s boiling pint is 36.5oC. Determine the molecular formula of this substance
Look up the normal boiling point of ether. Then delta T is difference between normal boiling point and 36.5.
delta T = Kf*m
Substitute and solve for m = molality.
Molality = mols/kg solvent. 1g ether = 0.001 kg. Solve for mols.
Then mols = grams/molar mass. You know mols and grams, solve for molar mass.
Finally, molar mass/empirical mass = some number. Round to the nearest whole number which I'll call n and apply to this.
(CH2O)n
To determine the molecular formula of the substance, we need to find the molecular weight of the compound.
Step 1: Find the molar mass of the empirical formula.
CH2O has the following molar masses:
C = 12.01 g/mol
H = 1.01 g/mol x 2 = 2.02 g/mol
O = 16.00 g/mol
Total molar mass of CH2O = 12.01 + 2.02 + 16.00 = 30.03 g/mol
Step 2: Find the number of empirical formula units in 0.0866 g of the compound.
Number of empirical formula units = 0.0866 g / 30.03 g/mol = 0.002885 mol
Step 3: Find the molar mass of the compound.
To do this, we need the molecular weight of the compound in grams.
Molecular weight = (mass of the compound in grams) / (number of moles of the compound)
We know that 0.0866 g of the compound is dissolved in 1.0 g of ether, so the total mass of the compound is 0.0866 + 1.0 = 1.0866 g
Molecular weight = 1.0866 g / 0.002885 mol = 376.72 g/mol
Step 4: Determine the molecular formula.
To determine the molecular formula, we need to find the ratio between the molar mass of the empirical formula and the molar mass of the compound.
Molecular formula = (molar mass of the compound) / (molar mass of the empirical formula)
Molecular formula = 376.72 g/mol / 30.03 g/mol
Molecular formula = 12.53
Since the molecular formula needs to be a whole number, we need to multiply the empirical formula by this number to obtain the molecular formula.
Multiplying CH2O by 12.53, we get:
Molecular formula = (C12H2O12)
Therefore, the molecular formula of the substance is C12H2O12.
To determine the molecular formula of a substance given the empirical formula, we need to know the molar mass of the compound. We can calculate the molar mass of the substance using the empirical formula.
1) Determine the molar mass of each element:
- Carbon (C): atomic mass = 12.01 g/mol
- Hydrogen (H): atomic mass = 1.01 g/mol
- Oxygen (O): atomic mass = 16.00 g/mol
2) Calculate the molar mass of the empirical formula:
- Molar mass of CH2O:
= (12.01 g/mol * 1) + (1.01 g/mol * 2) + (16.00 g/mol * 1)
= 30.03 g/mol
3) Next, find the number of empirical formula units in one molecule of the compound:
- Divide the molar mass of the compound (determined experimentally) by the molar mass of the empirical formula.
- In this case, we have 0.0866 g dissolved in 1.0 g of ether. The boiling point elevation is due to the total mass of the compound in the solution.
- Mass of compound in solution = 0.0866 g + 1.0 g = 1.0866 g
4) Determine the number of empirical formula units:
- Number of empirical formula units = mass of the compound in solution / molar mass of the empirical formula
- Number of empirical formula units = 1.0866 g / 30.03 g/mol
- Number of empirical formula units ≈ 0.03618 mol
5) Finally, determine the molecular formula:
- Divide the molar mass of the compound by the molar mass of the empirical formula units to find the ratio of empirical formula units to actual molecules.
- Molecular formula = empirical formula * n
- empirical formula: CH2O
- n: Number of empirical formula units
- n ≈ 0.03618 mol
- The molecular formula is CH2O.
Therefore, the molecular formula of this substance is also CH2O, which is the same as the empirical formula.