I don't understand how first of all the compound went from having a total mass of 10.68 mg? to gaining a mass of 20.38 mg?
The compound (10.68 mg) was burned - it combined with oxygen (9.70 mg) to produce products with a total mass of 20.38 mg.
Also, how do you get the mole number for carbon in "16.01 mg CO2 = 0.364 mmol CO2 --> contains 0.364 mmol C: mass = 4.369 mg", are you not taking the amu of oxygen into account in order to get .364?
The molar mass of CO2
is 44 g/mol. Therefore mmol CO2
= 16.01/44 = 0.364 mmol
For every 1 CO2
molecule, there is 1 C atom
For every 1 mol of CO2
molecules, there is 1 mol of C atoms
For every 0.364 mmol of CO2
molecules, there is 0.364 mmol of C atoms
Calculate the mass of 0.364 mmol of C atoms.
An important thing to understand is that all of the C in the products originated in the starting material, and the same is true for the H. Some of the O came from the starting material, and some came from oxygen gas: