How do I do this empirical formula problem?
A 1.547g sample of a component of the light petroleum distillate called naphtha is found to yield 4.742 g CO2 and 2.264g H2O on complete combustion.
This particular compound is also found to be an alkane with one methyl group attached to a longer carbon chain and to have a molecular formula twice its empirical formula.
The compound also has the following properties:
melting point of -154 degree C ,
boiling point of 60.3 degree C ,
density of 0.6532 g/mL at 20 C ,
specific heat of 2.25 J/(gC}) , and
Delta Hf= -204.6 kJ/mol .
Comments
Conservation of mass tells us that all the C and H from the sample must be present in the products.
So use the mass of CO2 and H2O to determine the moles of C and H that were in the original sample
moles = mass / molar mass
moles CO2 = 4.742 g / 44.01 g/mol = 0.1077 moles CO2
each CO2 has 1 C atom, therefore moles C = 0.1077 moles
moles H2O = 2.264 g / 18.016 g/mol = 0.1257 moles H2O
each H2O has 2 moles H
Therefore moles H = 2 x moles H2O = 0.2513 moles H
Now you know moles of C and H in the hydrocarbon place them in ratio format
moles C : moles H
= 0.1077 mol : 0.2513 mol
divided each number in the ration by the smallest number
C : H
(0.1077 / 0.1077) : (0.2513 / 0.1077)
= 1 : 2.33
Thisi is not a whole number ratio yet... multiply the whole ratio by the smallest number required to end up with all whole numbers (in this case 3)
3 x (1 : 2.33)
= 3 : 7
empirical formula is
C3H7
If the copper is heated strongly, you could assume that each and all the copper reacts. you already know the formula n = m/M or type of moles = mass/molar mass? you could artwork out what number moles of copper you began with, and for that reason what number moles of copper you end with. 10.04/sixty 3.fifty 5 = 0.158 moles. you already know the mass of oxygen you finally end up with, so which you would be able to artwork out what number moles of oxygen you have. 2.fifty 3/sixteen = 0.158 moles. you already know which you're in basic terms going to make an oxide (ie no different species would be present day in this compound) so which you have a a million:a million ratio of moles. hence you have CuO.