combustion analysis of a 285.7 mg sample of a hydrocarbon produces 880.8 mg of CO2 ans 405.7 mg of H2O.

What is the empirical formula of the compound?
a rough measurement of the molecular weight indicates it is a little over 100mg/mol. what is the molecular formula of the compound?

I don't know how to get the answer.

To find the empirical formula of the compound, we need to calculate the mole ratio of carbon and hydrogen in the hydrocarbon. Here are the steps to solve the problem:

Step 1: Convert the given masses of CO2 and H2O to moles.
The molar mass of CO2 is 44 g/mol, so the moles of CO2 can be calculated as: moles(CO2) = mass(CO2) / molar mass(CO2)
moles(CO2) = 880.8 mg / 44 g/mol = 0.0200 mol

The molar mass of H2O is 18 g/mol, so the moles of H2O can be calculated as: moles(H2O) = mass(H2O) / molar mass(H2O)
moles(H2O) = 405.7 mg / 18 g/mol = 0.0225 mol

Step 2: From the stoichiometry of the combustion reaction, determine the ratio of moles of carbon to moles of hydrogen.
From the balanced combustion equation, we know that for every 1 mole of carbon reacted, 1 mole of CO2 is produced, and for every 2 moles of hydrogen reacted, 1 mole of H2O is produced.

Since the mole ratio of carbon to CO2 is 1:1 and the mole ratio of hydrogen to H2O is 2:1, we can conclude that the mole ratio of carbon to hydrogen in the hydrocarbon is also 1:2.

Step 3: Divide the moles of carbon and hydrogen by the smallest mole value to get the simplest whole number ratio.
Since the ratio of carbon to hydrogen is 1:2, divide moles(C) and moles(H) by 0.0200, which is the smallest mole value:
moles(C) = 0.0200 mol / 0.0200 mol = 1
moles(H) = 0.0225 mol / 0.0200 mol = 1.125 ≈ 1.13

The simplest whole number ratio is C1H1.13. Since we cannot have a fraction in the empirical formula, we need to multiply the subscripts by a common factor to make them whole numbers. The closest whole number multipliers are 2.

So, the empirical formula of the compound is C2H2.

To determine the molecular formula of the compound based on the given information that the molecular weight is a little over 100 mg/mol, you need to divide the molar mass of the compound by the empirical formula mass (sum of the atomic masses of the empirical formula).

The molar mass of the empirical formula C2H2 is:
(2 * molar mass of C) + (2 * molar mass of H) = (2 * 12 g/mol) = (2 * 1 g/mol) = 26 g/mol

Divide the given molecular weight (a little over 100 mg/mol) by the empirical formula mass (26 g/mol):
100 mg/mol / 26 g/mol = 3.85

Since the result is approximately 3.85, it means that the molecular formula of the compound is approximately 3.85 times the empirical formula.

So, the molecular formula is approximately 3.85 * C2H2 = C7.7H7.7.

However, we cannot have fractional subscripts in the molecular formula, so we need to round these numbers to the nearest whole numbers. Thus, the most likely molecular formula for the compound is C8H8.