# 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
• 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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