Chemistry: How Much?

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  • Chemistry:  how much?
    • the mole
      • 6.023 x 10 to the 23
      • mole of atom or molecule weighs exact same in grams as relative atomic mass
      • number of moles = mass in g / relative formula mass
      • relative masses are compared to carbon 12
    • reacting masses and empirical formulas
      • 42.9g of K in 61.6g KOH
      • 42.9 / 61.6 x 100 = 60.6%
      • simplest ratio of atoms in a compound
      • chemical formula - C6H12O6
      • empirical formula - CH2O
    • concentration
      • moles per dm3
      • concentration = number of moles / volume
      • mass = number of moles / relative formula mass
      • GDA's per 100g or 100ml
      • use sodium content to estimate mass of salt
    • titrations
      • add alkali to conical flask
      • add three drops of indicator
      • fill a burette with the acid
      • add acid to alkali slowly
      • indicator changes colour when neutralised
      • record volume of acid needed
      • should try to get several consistent readings
      • use single indicators to find exact point
      • start with 25cm3
      • concentration is 0.100 moles per dm3
      • takes 49cm3 to neutralise
    • gas volumes
      • gas syringe
      • upturned measuring cylinder or burette
      • measure on scales
      • one mole of gas occupies 24dm3
    • following reactions
      • reactions stop when one reactant is used up
      • reactant used up is limiting reactant
      • product is directly proportional to limiting reactant
      • more reactant particles from more reactant
      • steeper curves mean faster reactions
      • more limiting reactant creates a faster reaction time
    • equilibrium
      • the products of the reaction can themselves react to produce the original reactants
      • when both reactions are at the same rate, there is an equilibrium
      • this can only happen if the products cannot escape
      • effects: temperature, pressure, concentration
      • on left - more reactants
      • on the right - more products
    • changing equilibrium
      • if you decrease temperature, equilibrium increases it
      • if you increase pressure, equilibrium tries to decrease it
      • if you increase concentration, equilibrium makes more products
    • the contact process
      • used to make sulfuric acid
      • make sulfur dioxide
      • sulfur dioxide oxidised
      • sulfur trioxide makes sulfuric acid
      • uses 450 degrees temperature
      • one atmosphere used
      • catalyst is used which doesn't affect the equilibrium
    • strong and weak acids
      • acids produce protons in water
      • strong acids ionise completely in water
      • weak acids do not fully ionise
      • ionisation of the weak acid is a reversible reaction
      • strong acids have a pH of one or two
      • weak acids have pH of five or six
      • strong acids are better electrical conductors as they have more ions
      • strong acids react faster
    • precipitation reactions
      • ionic substances must be liquid
      • a solid precipitate is formed
      • chloride - white
      • bromide - cream
      • iodide - yellow
    • preparing insoluble salts
      • mix all ions
      • precipitate, filter, and dry
      • put onto paper and leave to dry

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