amount of substance- chapter 3 Flashcards
what is the amount of substance
a quantity to count the number of particles in a substance, measured in a unit called mole
what is the Avogadro’s constant
6.02x10^23mol-1
what is molar mass
gives a convenient way of linking moles with mass for any chemical substance
how to calculate the amount of substance
mass/molar mass n=m/M
what is the molecular formula
the number of atoms of each element in a molecule
what is the empirical formula
the simplest whole number ratio of atoms of each element in a compound
what is the relative molecular mass Mr
compares the mass of a molecule with the mass of a f an atom of carbon-12
add the relative atomic masses together to find
what is the relative formula mass
compares the mass of a formula unit with the mass of an atom of carbon-12
calculated by added together the relative atomic masses of the elements in the empirical formula
what does hydrated mean
water molecules are part of their crystalline structure
what is water of crystallisation
when blue crystals of hydrated copper(II) sulfate are heated, bonds holding the water within the crystals are broken and the water id driven off, leaving behind white anhydrous copper (II) sulfate
CuSO4.5h2O=CuSO4 + 5H2O
what are the 2 assumptions from how accurate water of crystallisation is
- all of the water has been lost
if the hydrated and anhydrous forms have different colours, you can be fairly sure when all the water has been removed. however you only see the surface of the crystals and some water could be left inside. if the anhydrous and hydrated forms are similar colours, it is not as easy
solution= heat until a constant mass so its certain all water has been removed - no further decomposition
many salts decompose further when heated. this can be difficult to judge if there is no colour change
what is needed to work out the moles
volume and the concentration of the the solute
mol=c x v
what is a standard solution
a solution of known concentration
how are standard solutions prepared
by dissolving an exact mass of the solute in a solvent and making up the solution to an exact volume
what is the molar gas volume
the volume per mole of gas molecules at a stated temperature and pressure (many at RTP= 24dm3mol-1
what is the equation of moles with gas
mol= volume/molar gas volume
what are the 4 assumptions on the ideal gas equation
- random motion
- elastic collision
- negligible size
- no intermolecular forces
what is the ideal gas equation
pV=nRT
R=8.314
what is stoichiometry
in a balanced equation, the balancing number give the ratio of the amount of moles of each substance
what is the theoretical yield
the maximum possible amount of product
why is the theoretical yield hard to obtain (3)
- reaction may have not gone to completion
- other reaction (side reactions) have taken place alongside the main
- purification of the product may result in loss of some product
what is the percentage yield equation
actual yield/theoretical yield x100
what is the limiting reagent
the reactant that is not in excess and that’s completely used up
what is atom economy
a measure of how well atoms have been utilised
what is the atom economy equation
sum of molar masses of desired products/sum of molar masses of all products x 100
what are 2 good reasons for atom economy
- produce a larger proportion of desired products and a few unwanted
- more important for sustainability as they make use of natural resources
