there are many calculations using the mole ;
- number of particles = moles x Avogadro's constant (6.02x10^23)
- number of moles = mass / Mr
- number of moles = concentration (moldm^-3) x volume (dm^3)
the ideal gas equation
pV = nRT
p - pressure (pa)
V - volume (m^3)
n - moles
R - gas constant (8.31 jk^-1mol^-1)
T - temperature (k - +273 degrees)
masses from equations
- 1 - write out balanced equation
- 2- find the Mr of given compound
- 3- from the given mass, find moles by mass/Mr
- 4- use the ratios in the equation and the calculated moles to find the moles of the required compound
- 5- find the Mr of the require compound
- 6- use the Mr and moles to find the mass by mol / Mr
empirical formula by % mass
- 1 - match each element to it's % and find its Mr
- 2- find the moles of each element by % / Mr
- 3 - divide each of the moles by the smallest number of moles you have calculated
- 4- this is the ratio of elements, use this to write the formula
empirical formula by experimental data
- 1- find the moles of each element by mass / Mr
- 2- find the ratio of moles by dividing all the mol values by the smallest mol value you have calculated.
- 3- use this to write your emprical formula.
concentrations from titrations
- 1- write a balanced equation for the compounds you need
- 2 - work out the moles of the compound given using conc. x vol.
- 3- use the mole ratios from the equation to work out the moles of the required compound
- 4- use conc. = mol / vol to find concentration.
- 1 - find the theoretical yield by:
- a - use mass / Mr to find moles of the given product
- b - use mole ratios from the balanced equation to find moles of required compound
- c - find the mass by moles x Mr
- 2 - substitute this into this equation:
- % yield = actual yield / theoretical yield
- you will be given the actual yield
% atom economy = Mr of desired product / sum of Mrs of all reactants x 100
- 1 - find the bonds broken, use the balanced equation. add their mean bond enthalpy values.
- 2- do the same for bonds made
- 3- minus the value for bonds made from the value of bonds broken to give total change.
- enthalpy change = total energy absorbed - total energy released.