1.2 amount of substance Flashcards
how many particles are in a mole?
6.022 x 10^23
no of particles=
no of moles x avogadros constant
moles=
mass/Mr
What is the ideal gas equation?
lets you find no of moles in volume at any temp and pressure
pV=nRT
Pa, m^3, mol,8.31JK-1mol-1, k (add 273)
what is an ionic equation?
only includes reacting particles and products
1) balance equation
2) rewrite as ions
3)remove anything on both sides
4) check charges are balanced
how do you work out calculating masses?
1) write balanced equation
2)work out how many moles of reactant you have
3) use molar ratio to find how many moles of product will be formed
4) calculate mass of product
dont use big nos in Ar as these are taken into account with ratio
How do you calculate gas volumes?
1) balance equation
2) find moles of reactant
3)use molar ratio to find moles of product
4) put moles of product into ideal gas equation
what is a titration?
neutralisation reaction to find conc of acid/ alkali solution
2 indicators used in titrations?
methyl orange is red in acid and yellow in alkali
phenolphthalein is colourless in acid and pink in alkali
How do you do a titration calculation?
draw table of acid, alkali and conc, vol, mol
fill in what know (vol in dm3
work out moles you can
use molar ratio to find other moles
find conc
what is the empirical formula?
smallest whole number ratio of atoms of eahc element in a compound
what is the molecular formula?
actual number of atoms in a molecule
how do you work out molecular formula from empirical
1) find empirical mass by adding up Ar of each atom eg 83
2) divide molecular mass by empirical eg 166/83=2
3) do empirical formula x answer to 2 eg C4H302 X 2 = C8H604
how do you calculate empirical formula from the percentage composition of elements in a compound?
1) calculate moles of each element by doing % or mass (assume you’ve got 100g of compound) / Ar
2) divide each no of moles by smallest no of moles you found to get the ratio
3) may have to multiply to get whole numbers
What is maximum theoretical yield?
the yield you would get assuming no chemicals are lost.
how do you work out chemical yield?
% yield = (actual/ theoretical) x100
theoretical- reacting masses
what is atom economy?
measure of proportion of reactant atoms that become part of the desired product. reactions have have 100% yield but still low atom economy
What can you do with the by-products if dont have 100% atom economy?
sell them
Advantages of high atom economy
- economic- waste of money if lots of reactant ends up as useless byproduct, lots of money to separate product you want from others, waste products need to be safely disposed of- expensive
- environmental and ethical- use raw materials efficiently so they last longer. produce less waste which can be harmful to environ, companies can find easier, cheaper ways to produce medicine etc so sold cheaper
How do you work out % atom economy?
(mass of desired products / mass of all reactants) x100
USE big nos when calculating molecular mass
What is the limiting reagent?
reactant that is used up first so controls the amount of reaction you get. other reactant is in excess
How do you work out the limiting reagent?
determine the number of moles of each reactant
compare molar ratio of reactants with ratio in balanced chem equation to determine which is limiting
What is water of crystalisation?
water that is chemically bonded into a crystal structure
do anhydrous and hydrated mean?
anhydrous- contains no water of crystallisation-powder
hydrated- contains water of crystallisation- crystal
how do you workout water of crystallisation by heating it?
findmass of each component (compound and water) using conservation of mass
find the moles of each
divide by the lowest moles to find the ratio
How do you do a TOF calculation?
rearrange Ek=1/2mv^2 to find the velocity of an ion
use t=v/d to find time for ion to travel
combined equation is
t= d x square root of (m/2KE)
may need to use moles=no of particles/ avogadros constant
practicals in this topic
titrations
why might the experimental value and correct value for X in water of crystallisation be different?
sample wasnt heated until a constant mass