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c5 (titration (use a pipette, measure set volume of alkali into flask, add…
c5
titration
allows you to find out how much acid is needed to neutralise a given quantity of alkali or vice versa
use a pipette, measure set volume of alkali into flask, add drops of indicator, phenolphthalein or methyl orange
not universal, changes colour gradually, want single colour change
fill burette w standard solution or known concentration of acid, use burette to add acid a bit at a time, swirl flask regularly, go drop at a time when almost neutralised
indicator changes colour when all alkali neturalised, phenolph is pink in alkalis and colourless in acids, methyl is yellow in alkalis, red in acids
record volume of acid used to neutralise the alkali, the titre, repeat a few times, then calculate mean
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gas calculations
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under same conditions, same number of moles of different gases all occupy same volume
one mole of any gas always occupies 24dm cubed at room temp and pressure (RTP = 20 degrees and 1 atmosphere)
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atom economy
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100% means all atoms in the reactants are turned into desired products, higher the greener
low use up resources quickly, make lots of waste that have to be disposed of, reactions are unsustainable, raw materials will run out and waste has to go somewhere
low reactions aren't usually profitable, raw materials are expensive, waste products expensive to dispose of
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must consider percentage yield, rate of reaction and if it's reversible
rate experiments
show how surface area affects reaction rate, put marble chips in dilute HCl in a flask, CO2 gas will be released into gas syringe, time it
measure vol of gas produced, read at regular time intervals, plot graph, repeat with same volume and conc of acid and same mass of chips but more crunched, then powdered chalk, all made of calcium carbonate, CaCO3
finer particles means larger surface area, faster reaction
magnesium metal in dilute HCl, shows effect of changing concentration, gives off hydrogen gas, can measure loss of mass as gass is formed
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dynamic equilibrium
reversible reactions go forwards and backwards, products can react to produce original reactants, go both ways
reactants react, concs fall, forward reaction slows, as more of products are made, concs rise, backward reaction speeds up
after a while, forward reaction will go at same rate as the backward one, equilibrium
at equilibrium both reactions are happening, no overall effect, dynamic equilibrium, concs of reactant and products have reached a balance and won't change
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collision theory
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increasing temp increases rate, more particles collide with more energy to react, move faster
increasing pressure and conc means more particles of reactant in the same volume, or particles more crowded, collsions more likely and frequency of collsions increases
smaller solid particles/more surface area increases rate, smaller pieces increase surface area to volume ratio, more area to work on, collision frequency will increase
le chatelier
change in conc, pressure or temp in a reversible reaction will cause equilibrium position to move to help counteract that change
temp : all reactions are exothermic in one direction and endothermic in the other
decrease temp, equi moves in exothermic direction to produce more heat
increase temp, equi moves in endothermic direction to absorb extra heat
pressure : increase pressure, equi moves to side w fewer moles of gas to reduce pressure
decrease pressure, equi moves to side w more moles of gas to increase pressure
conc : increase conc of reactants, equi moves to right to use up reactants to make more product
increase conc of products, equi moves to left to use up products to make more reactant
decreasing causes opposite effect
concentration
more solute dissolved in a given volume, more crowded the molecules and more concentrated the solution
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often in moles per dm cubed, to convert from g/dm cubed to mol/dm cubed, divide concentration in g/cm by relative formula mass of solute
percentage yield
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always between 0 and 100, if low then lots of reactants are wasted, important to use reactions with highest possible yield to reduce waste and keep costs low as possible
precipitation
works for any reaction where mixing two see through solution produces a precipitate which clouds the solution
mix the two reactant solutions, put flask on paper with a mark
measure how long it takes for mark to be obscured, faster disappears, faster reaction
catalysts
increases rate of reation, isn't used up, only need a small amount to catalyse large amounts of reactants
work by decreasing activation energy needed for a reaction to occur, provide an alternative reaction pathway with a lower activation energy
enzymes are biological catalysts, catalyse chemical reactions in living cells, reactions catalysed by enzymes inc respiration, photosynthesis and protein synthesis
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change in mass
as gas is released, lost mass is measured on balance, quicker reading drops, faster reaction
do in fume cupboard, gas might be harmful, cotton wool lets gases through but stops other reactants
right or left
a reaction at equilibrium doesn't mean the amounts of products and reactants are equal, sometimes tilts to right meaning more product conc, sometimes tilts to left meaning more reactant conc
temp, pressure and concentration can change the position
volume of gas
gas syringe to measure volume of gas given off, more gas in a time interval, faster the reaction, syringe must be right size, if reaction too vigorous, can blow plunger out the end