when a hydrocarbon was completely burned in air ,5.28 g carbon 4 oxide and 2.16g of steam was produced given that the hydrocarbon has a relative formula mass of 84 determine its molecular formula(c=12,h=1,o=16)
To determine the molecular formula of the hydrocarbon, we need to use the information provided about the amounts of carbon dioxide and steam produced when it is burned in air.
From the balanced chemical equation for the combustion of a hydrocarbon in air:
hydrocarbon + O2 → CO2 + H2O
we can see that each mole of hydrocarbon that is burned will produce one mole of carbon dioxide and one mole of water.
To calculate the number of moles of carbon dioxide and water produced in the combustion reaction, we first need to convert the given masses of each product to moles:
moles of CO2 produced = 5.28 g / 44 g/mol = 0.12 mol
moles of H2O produced = 2.16 g / 18 g/mol = 0.12 mol
Since each mole of hydrocarbon will produce one mole of carbon dioxide and one mole of water, we know that the number of moles of hydrocarbon burned must also be 0.12 mol.
The relative formula mass of the hydrocarbon is given as 84 g/mol, so its empirical formula mass can be calculated by dividing by the smallest whole number ratio of atoms in the compound. To do this, we need to find the ratio of carbon to hydrogen atoms in the empirical formula:
mass of C in empirical formula = (0.12 mol of CO2) x (1 mol of C / 1 mol of CO2) x (12 g/mol) = 1.44 g
mass of H in empirical formula = (0.12 mol of H2O) x (2 mol of H / 1 mol of H2O) x (1 g/mol) = 0.24 g
ratio of C to H = 1.44 g / 0.24 g = 6:1
This means that the empirical formula of the hydrocarbon is C6H, which has a formula mass of 6(12) + 1(1) = 73 g/mol.
To find the molecular formula of the hydrocarbon, we need to determine the number of empirical formula units present in one molecule of the compound. This can be done by dividing the given molecular mass by the empirical formula mass:
molecular formula units = 84 g/mol / 73 g/mol = 1.15
Since we need a whole number of empirical formula units, we can round this value to the nearest integer, which is 1.
Therefore, the molecular formula of the hydrocarbon is C6H6.