s1.4 counting atoms by mass: the mole

• avogadro's constant

  6.02 x 10^23
• relationship between number of particles, moles and avogadro's constant

  number of particles = moles (mol) x avogadro's constant (mol^-1)

  N = n x Na
• relationship between mass, moles and molar mass

  mass (g) = moles (mol) x molar mass (gmol^-1)

  m = n x Mr
• empirical formula

  the empirical formula of a compound is the simplest ratio of atoms of each element present in that compound
• molecular formula

  the molecular formula gives the actual number of atoms of each element present in a molecule
• how to determine the molecular formula of a compound from its empirical formula and molar mass

  calculate molar mass of empirical formula

  divide actual mass by empirical formula mass

  multiply whole number by empirical formula to get molecular formula
• relationship between moles, concentration and volume

  moles (mol) = concentration (moldm^-3) x volume (dm^3)

  n = c x V
• convert between cm^3 and dm^3

  1 dm^3 = 1000 cm^3

  1000 cm^3 = 1 dm^3
• relative atomic mass definition

  the ratio of the mass of a certain atom to 1/12 of the mass of a C-12 atom (Ar)
• relative molecular mass definition

  the ratio of the mass of a molecule to 1/12 of the mass of a C-12 atom (Mr)