amounts of substance

• Why is the term relative formula mass used for ionic compounds?

  because ionic compounds don't exist as molecules
• Relative atomic mass (Ar)

  The weighted average mass of an atom of an element (taking into account isotopes) compared with 1/12 of the mass of an atom of carbon-12.
• How is the Ar calculated?


  average mass of 1 atom of an element/ 1/12 mass of a carbon-12 atom
• what is the equation to find the number of moles in a given solution?


  number of moles in solution = [concentration (mol dm^-3) x volume (cm^3)] /1000
• Boyle's Law


  when temperature is constant, pressure is inversely proportional to volume (P x V = constant)
• Charles' Law


  volume is directly proportional to temperature as long as pressure remains constant (V/T= constant)
• Gay-Lussac's Law (constant volume law)


  The pressure is proportional to the temperature as long as the volume remains constant (P/T = constant)
• Which equation relates pressure (P), volume (V) and temperature (T) ?


  (Pressure x Volume) / temperature= constant for a fixed mass of gas
• Ideal Gas Equation


  PV=nRT

  where P = pressure, V= volume, n = number of moles, R = the molar gas constant and T = temperature.
• How do you convert Celsius to Kelvin?


  add 273.15
• What is the empirical formula?


  An empirical formula is the simplest ratio of whole number atoms of each element in a compound.
• what are the steps to find empirical formula?


  1) find the masses of each of the elements present in a compound

  
  

  2) work out the number of moles of atoms of each element

  
  

  3) convert the numbers of moles if each element into a whole number ratio
• how is percentage yield calculated?


  Actual yield divided by theoretical yield, multiplied by 100
• relative molecular mass (Mr) in terms of 12C

  the mass of that molecule compared to 1/12 the relative atomic mass of carbon-12
• how is Mr calculate?

  Average mass of one molecule/ 12th the mass of a 12C atom
• Define the Avogadro constant

  the number of atoms in 12g of carbon-12
• Formula to find the number of moles in a particular mass

  n= m/M
• the mass of 1 mole of a substance is the same as

  the Mr