contain 85.7% carbon and an atomic mass of 84.0g/mol Determine the molecular 3. An unknown hydrocarbon composed of carbon and hydrogen atoms is found to formula.

To determine the molecular formula of the unknown hydrocarbon, we need to find the empirical formula first. Then, we can use the given molar mass to find the molecular formula.<br /><br />Step 1: Find the empirical formula<br />Given that the hydrocarbon contains 85.7% carbon, we can assume that there is 100g of the hydrocarbon. This means there is 85.7g of carbon in the hydrocarbon.<br /><br />To find the number of moles of carbon, we divide the mass of carbon by its atomic mass:<br />Number of moles of carbon = 85.7g / 12.01g/mol = 7.14 mol<br /><br />Since the hydrocarbon is composed of only carbon and hydrogen, the number of moles of hydrogen will be equal to the number of moles of carbon minus the number of moles of carbon:<br />Number of moles of hydrogen = 7.14 mol - 7.14 mol = 0 mol<br /><br />Therefore, the empirical formula of the hydrocarbon is CH.<br /><br />Step 2: Find the molecular formula<br />Given that the molar mass of the hydrocarbon is 84.0g/mol, we can use this information to find the molecular formula.<br /><br />The molar mass of the empirical formula CH is 13.02g/mol. To find the number of empirical formula units in the molecular formula, we divide the molar mass of the hydrocarbon by the molar mass of the empirical formula:<br />Number of empirical formula units = 84.0g/mol / 13.02g/mol = 6.47<br /><br />Since the number of empirical formula units must be a whole number, we round it to the nearest whole number, which is 6.<br /><br />Therefore, the molecular formula of the hydrocarbon is C6H6.