Question

Serotonin is a compound that conducts nerve impulses in the brain. it contains 68.2 mass percent c, 6.86 mass percent h, 15.9 mass percent n, and 9.08 mass percent o. its molar mass is 176 g/mol. part a determine its molecular formula.

Answer 1

C10H12N2O First, lookup the atomic weights of C, H, N, and O Atomic weight of Carbon = 12.0107 Atomic weight of Hydrogen = 1.00794 Atomic weight of Nitrogen = 14.0067 Atomic weight of Oxygen = 15.999 Now determine the ratio of atoms of each element by dividing their mass percentage by their atomic weights. Carbon = 68.2 / 12.0107 = 5.67827 Hydrogen = 6.86 / 1.00794 = 6.805961 Nitrogen = 15.9 / 14.0067 = 1.135171 Oxygen = 9.08 / 15.999 = 0.567535 Now determine a simple integer ratio of small integers that closely approximates the ratio of relative molar amounts. 5.67827 : 6.805961 : 1.135171 : 0.567535 Going to first divide all values by 0.567535 (picked because it's the smallest in the above ratios) getting 10.005 : 11.992 : 2.000 : 1 These numbers are all extremely close to integers so it looks like the empirical formula for Serotonin is C10H12N2O Let's compute the molar mass of the empirical formula 10 * 12.0107 + 12 * 1.00794 + 2 * 14.0067 + 15.999 = 176.2 g/mol Since that calculated molar mass matches the desired target, we're done. If the calculated mass was smaller, or the desired mass was larger (like 352 g/mol) we would have multiplied the number of atoms by the appropriate factor. But that's not needed, so the molecular formula for Serotonin is C10H12N2O