A 0.10g sample of C2H5OH (grey alcohol), known to contain only Carbon, Hydrogen, & Oxygen was burned to form the product CO2. A product was trapped separately and weighed 0.190g CO2 & 0.1172g H2O was found. What is the molecular formula of the compound if the molecular mass is 128g?
To determine the molecular formula of the compound, we need to find the empirical formula first and then use the molar mass to find the molecular formula.
1. Calculate the moles of CO2 and H2O produced:
- We know that the molar mass of CO2 is 44 g/mol. So, the number of moles of CO2 can be calculated as:
Moles of CO2 = Mass of CO2 / Molar mass of CO2
= 0.190 g / 44 g/mol
- Similarly, the number of moles of water (H2O) can be calculated as:
Moles of H2O = Mass of H2O / Molar mass of H2O
= 0.1172 g / 18 g/mol
2. Calculate the moles of carbon, hydrogen, and oxygen in the sample:
- From the balanced chemical equation, we know that for every mole of CO2 produced, there is 1 mole of carbon.
- Therefore, the number of moles of carbon in the sample = Moles of CO2
- From the balanced chemical equation, we know that for every mole of water (H2O) produced, there are 2 moles of hydrogen.
- Therefore, the number of moles of hydrogen in the sample = 2 * Moles of H2O
- Now, to find the number of moles of oxygen, we need to subtract the total number of moles of carbon and hydrogen from the total number of moles of CO2 and H2O:
Moles of oxygen = Moles of CO2 + Moles of H2O - (Moles of carbon + Moles of hydrogen)
3. Determine the empirical formula:
- Divide the moles of each element by the smallest number of moles among them to get the simplest ratio.
- Round the values to the nearest whole numbers to obtain the empirical formula.
4. Calculate the empirical formula mass:
- To calculate the empirical formula mass, sum up the atomic masses of the elements present in the empirical formula.
5. Find the molecular formula:
- Divide the given molecular mass by the empirical formula mass to determine the ratio between the molecular and empirical formulae.
- Multiply the subscripts in the empirical formula by this ratio to obtain the molecular formula. Round the values to the nearest whole numbers.
By following these steps, you can calculate the molecular formula of the compound.