complete combustion of a 0.0100mol sample of hydrocarbon, CxHy, gives 1.344 L of CO2 at STP and 0.720 g of H2O.
a. what is the molecular formula of hydrocarbon?
b. what is the empirical formula of hydrocarbon?..
1.344 L CO2 for 0.0100 mol sample would have evolved 134.4 L CO2 for a 1.00 mole sample. 134.4/44 = 3.05 moles C/mole unknown. So the formula is C3 H something.
0.720 g H2O for 0.01 mole would have evolved 72.0 g for a 1.00 mole sample and 72.0/18 = 3.99 moles H2O or that x 2 = 7.99 moles H atoms. So the molecular formula is C3H8 (3.05 rounds to 3.00 and 7.99 rounds to 8.00).
To find the molecular formula and empirical formula of the hydrocarbon, we need to analyze the data provided and use some chemical calculations.
a. To find the molecular formula:
1. Determine the molar mass of CO2: The molar mass of CO2 is 44.01 g/mol (12.01 g/mol for carbon + 2 * 16.00 g/mol for oxygen).
2. Convert the volume of CO2 to moles: We have 1.344 L of CO2 at STP. Using the ideal gas law (PV = nRT) and assuming the gas is ideal, we can calculate moles of CO2. At STP, 1 mole of any ideal gas occupies 22.4 L. So, we have 1.344 L * (1 mol/22.4 L) = 0.060 mol CO2.
3. Calculate the number of moles of carbon: Since the molar ratio between CO2 and C is 1:1, the number of moles of carbon is also 0.060 mol.
4. Calculate the number of moles of hydrogen: The number of moles of hydrogen can be determined using the mass of water produced. The molar mass of H2O is 18.02 g/mol (2 * 1.01 g/mol for hydrogen + 16.00 g/mol for oxygen). We have 0.720 g of H2O, so moles of H2O = 0.720 g * (1 mol/18.02 g) = 0.040 mol.
5. Determine the ratio of carbon to hydrogen: Divide the number of moles of carbon by the number of moles of hydrogen. In this case, the ratio is 0.060 mol C / 0.040 mol H = 1.5.
Now, we need to find the ratio of carbon to hydrogen in terms of whole numbers to determine the molecular formula.
Divide the ratio obtained in step 5 by its smallest value. In this case, the smallest value is 1.5, so we have 1.5 / 1.5 = 1 for carbon and 1.5 / 1.5 = 1 for hydrogen.
Therefore, the molecular formula of the hydrocarbon is CH.
b. To find the empirical formula:
The empirical formula represents the simplest, whole number ratio of atoms in a compound. In this case, the empirical formula is the same as the molecular formula since the ratio is already in its simplest form. Therefore, the empirical formula is also CH.