CHEM 3P40 Lecture Notes - Lecture 2: Chemical Formula, Elemental Analysis, Organic Compound

• School: Brock University
• Department: Chemistry
• Course: CHEM 3P40
• Professor: Costa Metallinos

Document Summary

Lecture 2: determination od the molecular formula of an unknown. Elemental analysis: complete combustion type cxhyoz co2 + h2o. Use the number of co2 and h2o to get the molecular formula. Example: 100mg of pure compound yields 275mg of co2 and 225mg of h2o. Take the masses of each co2 and h2) and divide them by their respective molecular weights: Calculate the number of moles of both c and h atoms, and divide by the smallest number of moles. In co2 there is only 1 carbon atom, therefore: 6. 25*1 = 6. 25. In h2o there are 2 atoms of h, therefore: 12. 5*2 = 25. Therefore we get the following empirical formula: ch4. Can you double ch4? (ch4)*2 c2h8 not possible! In this case, the empirical formula is also the molecular formula! Calculate the mass of c and h, then see if it accounts for the original mass. For c: 6. 25mmol * (12. 011mg*mmol-1) = 75mg. For h: 25mmol * (1. 0079mg*mmol-1) = 25mg.