Combustion analysis, Empirical and Molecular formulas, help!?

When 2.686 grams of a hydrocarbon, CxHy, were burned in a combustion analysis apparatus, 9.224 grams of CO2 and 1.511 grams of H2O were produced.

In a separate experiment, the molar mass of the compound was found to be 128.2 g/mol. Determine the empirical formula and the molecular formula of the hydrocarbon.

Enter the elements in the order presented in the qustion.

Start from a balanced equation

CxHy + (x+y/4)O2 -> xCO2 + y/2 H2O

so 1 mole of CxHy (molar mass 12x+y)produces
x mole of CO2 and
y/2 mole of H2O

so
2.686 g/(12x+y) moles

produces
9.224/44 =x moles of CO2
so x=0.2096

and produces

1.511/18=y/2 moles of H2O
so y=0.1679

so the ratio is
x:y
0.2096:0.1679
or 5:4

Thus the empirical formula or the simplest formula is
C5H4
for which molar mass is 64 g

we are told in the question that the molar mass is 128.2 g so the molecular formula (ie. the formula for one mole) must be C10H8, that is twice the empirical formula in this case.

you would divide the grams of each molecule produced by the smallest ratio to find the subscripts.

To determine the empirical and molecular formulas of the hydrocarbon, we need to follow a series of steps:

Step 1: Convert the masses of CO2 and H2O produced to moles.
To do this, we divide the given masses by their respective molar masses. The molar mass of CO2 is 44.01 g/mol and the molar mass of H2O is 18.02 g/mol.

Moles of CO2 = 9.224 g / 44.01 g/mol
Moles of CO2 ≈ 0.21 mol

Moles of H2O = 1.511 g / 18.02 g/mol
Moles of H2O ≈ 0.08 mol

Step 2: Use the mole ratios to determine the empirical formula.
The mole ratio is the relationship between the number of moles of the different elements in the compound. In the hydrocarbon, we have carbon (C) and hydrogen (H).

The mole ratio between carbon and carbon dioxide is 1:1 since the balanced equation for the combustion of hydrocarbons produces one mole of CO2 for every mole of carbon in the hydrocarbon.

The mole ratio between hydrogen and water is also 1:1 because every mole of water produced corresponds to one mole of hydrogen in the hydrocarbon.

Therefore, the empirical formula of the hydrocarbon is CH.

Step 3: Determine the molecular formula.
To find the molecular formula of the hydrocarbon, we need to know its molar mass. Given that the molar mass of the compound is 128.2 g/mol, we can compare the molar mass of the empirical formula to the actual molar mass.

The molar mass of CH is approximately 13.02 g/mol (carbon: 12.01 g/mol + hydrogen: 1.01 g/mol).

To calculate the ratio between the empirical formula mass and the actual molar mass, we divide the molar mass of the compound by the molar mass of the empirical formula.

Ratio = 128.2 g/mol / 13.02 g/mol
Ratio ≈ 9.84

The ratio tells us that the molecular formula is approximately 9.84 times the empirical formula.

As the empirical formula is CH, we multiply it by the ratio to find the molecular formula.

Molecular formula = CH * 9.84 ≈ C9H9

Therefore, the empirical formula of the hydrocarbon is CH, and the molecular formula is C9H9.

empirical formula is the smallest whole number ratio

molecular formula is the empirical doubled i believe.