Determine the empirical formula for a compound containing only c,h given that combustion of 1.50g sample of the compound produces 4.71g CO2 and 1.93g H2O
To determine the empirical formula of a compound, we need to know the mass or moles of each element present in the compound. In this case, we have the mass of carbon dioxide (CO2) and water (H2O) produced during combustion.
1. Start by determining the moles of carbon dioxide (CO2) and water (H2O) produced:
Moles of CO2 = mass of CO2 / molar mass of CO2
Moles of H2O = mass of H2O / molar mass of H2O
The molar masses of CO2 and H2O are:
Molar mass of CO2 = 12.01 g/mol (C) + 2 *16.00 g/mol (O) = 44.01 g/mol
Molar mass of H2O = 2 * 1.01 g/mol (H) + 16.00 g/mol (O) = 18.02 g/mol
Substituting the given masses:
Moles of CO2 = 4.71 g / 44.01 g/mol
Moles of H2O = 1.93 g / 18.02 g/mol
2. Convert moles of CO2 and H2O to moles of carbon (C) and hydrogen (H):
Since we know that the combustion of hydrocarbons only produces CO2 and H2O, we can determine the moles of C and H from these amounts.
Moles of C = 1 mole of CO2 contains 1 mole of C
Moles of H = 1 mole of H2O contains 2 moles of H
Moles of C = Moles of CO2
Moles of H = 2 * Moles of H2O
Substituting the moles calculated in step 1:
Moles of C = (4.71 g / 44.01 g/mol)
Moles of H = 2 * (1.93 g / 18.02 g/mol)
3. Find the ratio of moles of C to H:
Divide the moles of C and H by the smallest mole value to simplify the ratio.
Ratio of C to H = Moles of C / Moles of H
Divide both moles by the smallest mole value:
Ratio of C to H = (Moles of C / Mole ratio) / (Moles of H / Mole ratio), where Mole ratio is the smallest mole value calculated in step 2.
Simplify the ratio of C to H to the nearest whole number to obtain the empirical formula.
For example, if the ratio is 1.5, it can be rounded to 2. If the ratio is already close to a whole number, you may not need to round.
That's how you determine the empirical formula of a compound using combustion data.