C3-Quantitative Chemistry

• Percentage of an element in a compound

  Ar x number of atoms of that element

  ---------------------------------- x 100

  Mr of the compound
• Mole

  -Amount of a substance

  -1 mole= 6.02 x 10^23
• Mole formula

  mass in g

  ---------

  Mr
• Mass conserved in chemical reaction

  -No atoms destroyed or created

  -Same number of atoms in each side of reaction

  -No mass gained or lost
• Why mass changes

  1)If mass increases, one of reactants is a gas found in air and alll products are solids, liquids and aq

  -Before reaction, gas floating in air-not contained in reaction vessel, cant account its mass.

  -Gas reacts to form part product, contained inside the section vessel- total mass of stuff inside reaction vessel increase

  2)If mass decreases, one of products gas, all reactants solid, liquid,aq

  -Before reaction, reactants contained in reaction vessel

  -If vessel isn't enclosed, gas can escape from reaction vessel as its formed.No longer contained in reaction vessel, no mass
• Reaction stops when one reactant used up

  -Reaction stops when all of one of reactants is used up.Any other reactants are in excess.Usually added in excess to make sure other reactant all used up

  -Reactant used up in a reaction called limiting reactant

  -Amount of product formed directly proportional to amount of limiting reactant

  -If you add more reactant, will be more reactant particles to take part in the reaction, which means products particles
• Concentration

  amount of substance in a certain volume of a solution

  -More solute(the substance that is dissolved) there is in a given volume, more concentrated the solution
• Concentration formula

  concentration = mass of solute

  ------------------

  volume of solvent

  Units:

  Concentration= g/dm^3

  Mass= g

  Volume = dm^3