topic 5 - quantitative analysis Flashcards
titration
method of analysing the concentrations
allows you to find exactly how much acid is required to neutralise a given quantity of alkali or vice versa
pipette
measures one volume of solution
fill to above the line and then carefully drop the level down
burette
measures different volumes of solution
add solution drop to drop
scale down side of burette shows volume used
how to carry out a titration (8)
1) use pipette to measure out a set volume of alkali into flask
2) add a few drops of indicator (not universal, should be specific)
3) fill burette with standard solution of acid
4) use burette to add acid to alkali little by little at a time, swirling the flask regularly (when close to neutralisation, only add one drop at a time)
5) indicator changes colour once alkali is neutralised
6) record volume of acid used to neutralise - known as the titre
7) repeat process making sure to get similar results every time
8) calculate the mean
standard solution
solution of known concentration
molar concentration
concentration = number of moles/volume of solution
units concentration and conversion to mass concentration
mol/dm^-3
mol/dm^-3 to g/dm^-3 : multiply concentration by the RFM
how to calculate the concentration of another substance
work out moles of known substance using moles = concentration x volume
use balance equation to work out moles of other substance you should hve
work out concentration using concentration = moles / volume
molar volume
the volume occupied by one mole of gas
molar volume units and formula
dm^3mol^-1
molar volume = gas volume / number of moles
avogadro’s law
under the same conditions, the same number of moles of different gases all occupy the same volume
one mole of any gas always occupies 24dm^3 at room temperature and pressure (20°C and 1atm)
atom economy definition
the percentage of reactants changed to useful products
atom economy formula
(total Mr of desired products / total Mr of all products) x 100
100% atom economy meaning
all atoms in the reactants have been turned into useful products
reactions with low atom economies
they use up resources very quickly
make lots of waste products that need to be disposed of, tending to make reactions unsustainable
usually aren’t profitable as raw materials are expensive and disposing of waste materials is also expensive if done properly
way of dealing with the problem of waste products
use the waste products
choose a reaction that makes the desired product and also useful byproducts
percentage yield
the amount of product made compared to what should have been made
if there is a low percentage yield, lots of reactants will be wasted
percentage yield formula
(actual yield/ theoretical yield) x 100
hypothetical yield
mass of product you would make if all the reactants converted to products
what 3 factors can affect yield
incomplete reactions
practical losses
unwanted reactions
explain incomplete reactions as a factor that can affect yield
if not all of the reactants are converted to product, the reaction is incomplete and yield will be less than expected
explain practical losses as a factor than can affect yield
you lose a little bit when transferring chemicals between containers
explain unwanted reactions as a factor than can affect yield
if unwanted side reactions happen, yield decreases
unwanted reactions can be cause by impurities in reactants or changes to reaction conditions
4 factors to consider in industry
- atom economy
- percentage yield
- rate of reaction (must be fast enough to produce the amount needed in a sensible amount of time)
- if the reaction is reversible ( to keep yield high, you may need to alter the equilibrium position by changing conditions)
