Quick Recap — Composition & Formula Calculations

  • % C =1244×mass CO2mass sample×100=\dfrac{12}{44}\times\dfrac{\text{mass }CO_2}{\text{mass sample}}\times100; % H =218×mass H2Omass sample×100=\dfrac{2}{18}\times\dfrac{\text{mass }H_2O}{\text{mass sample}}\times100.
  • % halogen =at.mass Xmolar mass AgX×mass AgXmass sample×100=\dfrac{\text{at.mass }X}{\text{molar mass AgX}}\times\dfrac{\text{mass AgX}}{\text{mass sample}}\times100; % S via BaSO4BaSO_4 (×32233\times\tfrac{32}{233}).
  • Empirical formula: divide each % by atomic mass, take the simplest ratio; molecular =(empirical)n=(\text{empirical})_n.
  • Kjeldahl % N =1.4×Nacid×Vacidmass sample=\dfrac{1.4\times N_{acid}\times V_{acid}}{\text{mass sample}} (per mL of standard acid neutralised).