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what is a mole
amount of substance is measured using a unit called the mole (mol for short) . one mole is roughly 6 x 〖10〗^23 particles (Avogradro's constant) . It doesn't matter what the particles are . They can be atoms , molecules , electrons or ions

molar mass
molar mass , M , is the mass of one mole of something . But the main thing to remember is that molar mass is just the same as relative molecular mass M>r (or relative formula mass) . The only difference is you stick a "g mol^1" for grams per mole on the end

there's a formula that connects the molar mass of a substance to the number of moles of the substance that you have . it looks like this
 number of moles = mass of substance
 
 molar mass
 you can also rearrange the formula and use it to work out either the mass of a substance or its relative molecular mass

the concentration of a solution is
how many moles are dissolved per 1 dm^3 of solution . the units are mole dm^3 or (M)

here's the formula to find number of moles
 number of moles = concentration x volume
 (in cm^3)
 
 1000
 or
 number of moles = concentration x volume
 (in dm^3)

1 dm^3 is the same as
1000 cm^3 or 1 litre

note in the exam you may be asked to combine a concentration calculation with a molar mass calculation
:)

if temperature and pressure stay the same , one mole of gas always has the same
volume . at room temperature and pressure (r.t.p) this happens to be 24dm^3 (r.t.p. is 298 k (25 degrees centigrade) and 100kPa)

here are the two formulas for working out the number of moles in a volume of gas  don't forget only use them for r.t.p.
 number of moles = volume in dm^3/24
 or
 number of moles = volume in cm^3/24 000

in a real world , it's not always room temperature and pressure . the ideal gas equation lets you find the number of moles in a certain volume at any temperature and pressure
 pV = nRT
 p = pressure measured in pascals (Pa)
 V = volume measured in (m^3)
 n = number of moles
 R = gas constant whose value is given in the exam
 T = temperature measured in kelvin (K)

you might be given pressure in in kPa (kilopascals) . to convert from kPa to Pa you
multiply by 1000

you might be given temperature in degrees centigrade . to convert from degrees centigrade to K you
add 273

you might be given volume in cm^3 . to convert from cm^3 to m^3 you
multiply by 10^6

you might be given volume in dm^3 to convert from dm^3 to m^3 you
multiply by 10^3

how to balance equations
balanced equations have the same number of each atom on both sides . You can only add more atoms by adding whole compounds . You do this by putting a number in front of a compound or changing one that's already there . You can't mess with formulas

balancing ionic equations
in ionic equations only the reacting particles are included . You don't have to worry about the rest of the stuff . First you make sure that both sides have the same number of atoms  just like a normal equation . then you balance the charges by adding extra electrons

calculating masses  you can use a balanced equation for a reaction to work out how much product you will get from a certain mass of reactant . here are the steps to follow
 1) write out the balanced equation for the reaction
 2) work out how many moles of the reactant you have
 3) use the molar ratio from the balanced equation to work out the number of moles of product that will be formed from this much of reactant
 4) calculate the mass of that many moles of product

calculating gas volumes . here are the steps to follow
 1) write out the balanced equation for the reaction
 2) work out how many moles of the reactant you have
 3) use the molar ratio from the balanced equation to work out the number of moles of product that will be formed from this much of reactant
 4) put that number of moles into one of the gas equations

state symbols
 state symbols are put after each compound in an equation . they tell you what state of matter things are in
 s = solid
 l = liquid
 g = gas
 aq = aqueous (solution in water)

neutralisation
when an acid reacts with an alkali you get a salt and water

titrations allow you to find out
exactly how much acid is needed to neutralise a quantity of alkali

how to carry out a titration
 measure out some alkali using a pipette and put it in a flask , along with some indicator such as phenolphthalein .
 add the acid to the alkali using a burette  open the tap to run acid into the alkali a little bit at a time .
 every time you add some more acid , give the flask a swirl to make sure that the acid and the alkali are properly mixed .
 first of all do a rough titration to get an idea where the end point is . The end point of the titration is the exact point at which the indicator changes colour  at this point the amount of acid added is just enough to neutralise the alkali .
 now do an accurate titration . run the acid in to within 2cm^3 of the end point , then add the acid dropwise . If you don't notice exactly when the solution changed colour you've overshot and your result won't be accurate .
 record the amount of acid used to neutralise the alkali .
 It's best to repeat this process a few times , making sure you get the same answer each time . this will make sure your results are reliable

the apparatus needed for a titration

note in exam you need to be able to use the results of a titration to calculate the concentration of acids and alkalis
:)

n the exam you also need to be able to calculate the volume of acid or alkali that you need to neutralise a solution . you'll need to use the formula
 number of moles =
 concentration x volume (in cm^3)  1000
 but this time rearrange it to find volume
 volume (cm^3) = number of moles x 1000
 
 concentration

the empirical formula gives
just the smallest whole number ratio of atoms in a compound

the molecular formula gives the
actual numbers of atoms in a molecule . the molecular formula is made up of a whole number of empirical units

if you know the empirical formula and the molecular mass of a compound , you can calculate its molecular formula just follow these steps
 1) find the empirical mass  that's just the mass of the empirical formula
 2) divide the molecular mass by the empirical mass . this tells you how many multiples of the empirical formula are in the molecular formula
 3) multiply the empirical formula by that number to find the molecular formula

calculating empirical formulas
follow these steps each time
 1) [assume you have got 100g of the compound  you can turn the percentages into straight masses] . then you can work out how many moles of each element are in the compound by using number of moles=mass/mr
 2) divide each number of moles by the smallest number of moles you found in step 1 . this gives you the ratio of the elements in the compound
 3) apply the numbers from the ratio to the formula

monoprotic acids
acids that only release one H+ from each molecule

theoretical yield
mass of product that should be formed in a chemical reaction . it assumes no chemicals are lost in the process .

to calculate theoretical yield you can use the masses of reactants and a balanced equation . it's a bit like calculating reacting masses  here are the steps you have to go through
 1) work out how many moles of reactant you have
 2) use the equation to work out how many moles of product you would expect that much reactant to make
 3) calculate the mass of that many moles of product  and that's the theoretical yield

for any reaction , the actual mass of the product (the actual yield) will always be ... than the theoretical yield . There are many reasons for this . For example
 less
 sometimes not all the starting chemicals react fully . And some chemicals are always lost , e.g. some solution gets left on the filter paper , or is lost between transfers between containers

once you've found the theoretical yield and the actual yield , you can use work out the percentage yield by using the formula
 percentage yield = actual yield
  x 100
 theoretical yield

atom economy is one way to work out
how efficient a reaction is .

efficient reactions are better for
the environment and save the chemical industry money

the efficiency of a reaction is often measured by
the percentage yield . This tells you how wasteful the process is  it's based on how much of the product is lost because of things like reactions not completing or looses during collection and purification

percentage yield doesn't however measure
how wasteful the reaction itself is . A reaction that has a 100% yield could still be very wasteful if a lot of the atoms from the reactants wind up the in byproducts rather than the desired product .

atom economy is a measure of
the proportion of reactant atoms that become part of the desired product (rather than byproducts) in the balanced chemical equation

atom economy in industry
chemical companies try to use reactions that have a high atom economy , so they're not producing lots of waste , or spending money making byproducts . But reactions with low atom economy may still be used if the waste products can be sold and used for something else (waste products like gases , salts and acids can often be useful reactants for other products)

atom economy is calculated using this formula
 % atom economy
 mass of desired products
 =  x 100
 total mass of reactants

to calculate the atom economy for a reaction , you just need to
add up the molecular masses of the reactants , find the molecular mass of the product your'e interested in and put them both into the formual

any reaction where there's only one product has a % atom economy of
100

when you calculate the masses , you should use
the number of moles of each compound that is in the balanced equation

you should always calculate % atom economy from a
balanced equation

