C5

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  • Created by: Ellie
  • Created on: 27-05-13 14:23

MOLES

  • molar mass = relative formula mass in grams
  • thermal decomposition: metal carbonate --> metal oxide + carbon dioxide
  • no. of moles = mass of chemical / molar mass

Empirical formula:

  • 1) write down mass
  • 2) relative atomic mass
  • 3) stage 1 / stage 2
  • 4) choose smallest answer
  • 5) stage 3 / stage 4
  • % mass of element =( total mass of element in compound / relative formula mass of compound) X 100
  • if a solution is diluted 3 times, it will take up 3 times more volume
  • cm3 --> dm3 (divide by 1000)
  • dm3 --> cm3 (times by 1000)
  • n = c x v (n = number of moles, c = concentration, v = volume)
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GDA AND TITRATIONS

sodium:

  • good water balance
  • good nerve responses
  • high blood pressure
  • heart disease

Food labels must be read with care because some list the amount of sodium whereas some list salt.

Titrations:

  • acid + alkali --> salt + water
  • litmus - blue with alkali, red with acid
  • phenolphthalien - pink with alkali, colourless with acid
  • screened methyl orange - green with alkali, pink with acid

Measuring gas produced: upturned burette/measuring cylinder or a gas syringe

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GAS VOLUME AND EQUILIBRIUM

  • at rtp, 1 mole of gas takes up 24dm3
  • number of moles = volume of gas dm3 / 24
  • amount of product is proportional to limiting reactant 

Equilibrium achieved when...

  • rate of forward reaction = rate of backward reaction
  • concentrations of reactants & products don't change
  • if conc' of reactants > products - equilibrium position is to the left
  • if conc' of reactants < products - equilibrium position is to the right
  • temp increase = less product = equilibrium position to the left
  • pressure increase = more product = equilibrium position to the right

Le Chateliers Principle = if change is made in a closed system, the equilibrium will shift in a way to reduce the effect of change

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CONTACT PROCESS

sulfur dioxide + oxygen --> sulfur trioxide (equilibrium position to the right)

2SO2(g) + O2(g) --> 2SO3(g)

Conditions for contact process:

  • 450c - forward reaction is exothermic so high temp drives equilibrium to the left, high temp = faster reaction
  • atmospheric pressure - high pressure increases yield and drives equilibrium further to the right
  • vanadium catalyst - catalysts speed up reaction
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ACIDS

  • in water, acid molecules ionise
  • strong acid --> hydrogen ions + other ions, lots of H+ so seems very acidic, lots of collisions occur
  • weak acid --> hydrogen ions + other ions, forms equilibrium mixture (position = left), water contains lots of acid molecules and not many H+ ions so seems less acidic, fewer collisions
  • high concentration of H+ = low pH
  • low concentration of H+ = high pH
  • examples: HCl --> H+ + Cl- (strong), CH3COOH --> H+ + CH3COO- (weak)

Electrolysis: H+ ions move to cathode so ALL acids produce hydrogen at the cathode, stronger acids are more conductive.

  • acid concentration shows how many moles in 1dm3 of solution
  • acid strength shows degree of ionisation
  • concentrated solution of weak acid still has a low concentration of H+ ions
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PRECIPITATION REACTIONS AND SALT SAMPLES

ionic substances form lattices - they break apart in water and seperated ions can move

precipitation reaction:

  • involves mixing 2 ionic solutions
  • high collision frequency
  • fast reaction
  • looks like precipitate is formed instantly
  • AB + CD --> AD + CB
  • reaction between barium chloride + sulfate ions -  test for sulfate ions
  • lead nitrate + halide ions - test for iodide and chloride ions

Preparing insoluble salt:

  • 1) mix solutions to make barium sulfate and sodium chloride
  • 2) filter precipitate if barium sulfate
  • 3) wash with distilled water to remove traces of sodium chloride
  • 4) dry in warm place
  • lead nitrate + sodium iodide --> lead iodide + sodium nitrate (nitrate and sodium are spectators)
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