Module 2 - Amount of Substance Flashcards
define relative atomic mass
weighted mean mass of an atom relative to 1/12th of the mass of one atom of carbon 12
define relative formula mass
term used when working out the calculation for compounds with giant structures
examples of giant structures for relative formula mass
giant ionic, giant covalent, giant metallic
define relative molecular mass
term used when working out the calculation for compounds that are simple molecules
equation for percentage of an element
number of atoms of element x relative atomic mass of element / relative formula mass of compound x100
define molar mass
the mass per mol of a substance in g mol^-1
what does the mass of one mole equal
the ar of that substance
define amount of substance
chemists use amount of substance as a means of counting the number of particles in a substance. its unit is the mole (mol)
define avogadros constant
6.02 x 10^23. the number of atoms per mole of carbon 12
equation for number of atoms/ions/molecules
moles x 6.02x10^23
equation for number of mols
mass (g) / molar mass
units for molar mass
g mol -1
define molecular formula
the number and type of atoms in each element of a molecule
define empirical formula
shows the simplest whole number ratio of atoms of each element in a compound
steps to calculate empirical formula
- calculate number of moles
- divide number of moles by smallest value for a ratio
- adjust to make ratios whole numbers
define water of crystallisation
water molecules that are bonded into a crystalline structure of a compound
what does heated hydrated copper sulfate form
anhydrous copper sulfate + water
symbol equation for heating copper sulfate
CuSO4 . 5H2O -> CuSO4 + 5H2O
define hydrated
a crystallised compound containing water molecules
define anhydrous
contains no waters of crystallisation
method for calculating amount of water
-weigh the crucible
-add a known amount of hydrated salt
-weigh the crucible and hydrated salt together
-heat the hydrated salt strongly for a few minutes
-weigh and heat the sample until the mass stays constant
assumptions in calculating amount of water
-assuming all water has been lost by heating to constant mass
-when heating the salt its not breaking down further to other compounds
define molar gas volume
the volume per mole of gas molecules at the stated temperature and pressure (RTP)
room temperature
25 degrees
room pressure
101 kPa
what is the volume of a gas at RTP
1 mole of gas is 24.0dm^3
equation for volume of a gas in dm^3
moles = volume (dm3) / 24
equation for volume of a gas in cm^3
moles = volume (cm3) / 24,000
ideal gas equation
pV = nRT
degrees to kelvin conversion
add 273
kPa to Pa
add x10^3 on the end
cm^3 to m^3
add x10^-6 on the end
dm^3 to m^3
add x10^-3 on the end
ideal gas equation in words
volume x pressure = amount of gas x ideal gas constant x temperature
volume units in ideal gas equation
m^3
pressure units in ideal gas equation
Pa
amount of gas units in ideal gas equation
mol
temperature units in ideal gas equation
K
define stoichiometry
-the ratio, of the amount in moles, of each substance in a chemical reaction
steps for stoichiometry calculation
-write mr of substance known and unknown
-calculate moles of known
-ratio for moles of unknown
-work out question
steps for limiting reactant calculation
-calculate moles for both reactants
-do a ratio of how much you need for each one
-use the limiting reactant moles to work out the rest of the question
units for concentration
mol dm^-3
equation for number of moles (concentration)
volume x concentration / 1000
units of volume in concentration equation
cm^3
why do you divide by 1000 in the concentration equation
to convert volume to dm^3
what is percentage yield
the amount of product made from the starting materials
why does no reaction ever have 100% yield
-the reaction may have not gone to completion
-side reactions may have occurred
-purification of the product may have resulted in loss of product
percentage yield equation
actual moles/ theoretical moles x 100
percentage yield calculation steps
-workout mr or the reactant and product you have a mass for
-work out the actual moles (mass of the product)
-workout the theoretical moles (mass of the reactant-> ratio)
-put in equation
what happens in an ideal reaction
-all reactant atoms end up within the useful product molecule -no waste is produced
which reactions have low atom economy
-inefficient, wasteful reactions
which reactions have high atom economy
-efficient processes have high atom economy
why are high atom economy reactions important
-sustainable development
-conserve natural resources
-create less waste
atom economy equation
sum of molar masses of all desired products / sum of molar masses of all products x100
what is atom economy a measure of
-the proportion of reactant included in the final useful product
how are atom economy and percentage yield linked in a reaction
a reaction can have a
-high percentage yield
-low atom economy
what is the percentage atom economy if a reaction has 1 product
100%
define mole
the amount of any substance containing as many particles as there are carbon atoms in 12g of carbon 12 (6.02x10^23 particles)
which reactant do you use for theoretical moles in percentage yield if there are multiple
the limiting reactant
