5.3 quantitative chemistry

• law of conservation of mass

  no atoms are created or destroyed in a chemical reaction, so mass of products = mass of reactants
• relative formula mass (Mr) of a compound = sum of relative atomic masses of all the atoms in the compound
• change in mass during reaction = either reactant or product is a gas, has been lost to the surroundings
• whenever a measurement is made there is always some uncertainty about the result obtained
• the mass of one mole of a substance in grams is numerically equal to its relative formula mass
• mass = moles x Mr
• avogadro‘s constant 


  6.02 x 10^23
• total moles of one element must be the same on both sides of the equation
• limiting reactant 


  the reactant that is used up / not in excess
• in a chemical reaction with 2 reactants you will often use one in excess to ensure that all of the other reactant is used
• concentration is measured in g/dm^3
• mass = concentration x volume
• a smaller volume or larger mass of solute gives a higher concentration
• a larger volume or smaller mass of solute gives a lower concentration
• concentration of a solution can be measured in mol/dm^3
• moles = concentration x volume
• equal amounts of gases (in mol) occupy the same volume under the same conditions of temperature and pressure
• uncertainty = range of results / 2
• number of particles = number of moles x avogadro’s constant