Formulae, equations and amounts of substance Flashcards
Mole
amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.
Relative atomic mass
average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
Molar Mass
mass in grams of 1 mole of a substance and is given the unit of g mol-1
Gas volume (dm3)
mole x 24
cm3 –> dm3
divided by 1000
cm3 –> m3
÷ 1000 000
dm3 –> m3
÷1000
Avogadro constant
number of particles equivalent to the relative atomic mass or molecular mass of a substance
What is difference between relative molecular mass and relative formula mass
The mean mass of a molecule of a compound instead of mean mass of an atom of an element
What is empirical formula
simplest whole number ratio of atoms of each element in a compound
what is molecular formula
the actual number of atoms in the molecule . Determined by dividing the actual mr by the empirical mr
Ideal gas equation
pV = nRT
p = pascals
V = m3
T = Kelvin
n = moles
R = 8.31 J K -1mol-1
What is a titration
when a standard solution with a known concentration is reacted with solution of unknown concentration
How to make a volumetric/ standard solution
weight sample bottle
transfer solid and reweigh
record difference in mass add distilled water and stir with glass rod till dissolved
transfer to volumetric flash with washings and mark up with 250cm3 of distilled water
shake flask
How to carry out titration
measure standard solution into flash using volumetric pipette
add indicator
tap open portion by portion until colour change
multiple times carried out until concordant results obtained within 0.1cm3
formula for concentration
number of moles of solute divided by volume of solution.
concentrated solution has high conc of solute
how to work out mass when you have concentration and volume
conc x volume = n
n x molar mass = mass
what is two types of errors
random and systematic
what is a systematic error
poor designed procedure
if you forget to zero mass balance
don’t read burette at eye level
formula for uncertainty
( instrument uncertainty / measurement ) x 100
how can you reduce uncertainties
increase titre volume either increase volume and concentration in flask or decrease concentration in burette
percentage yield
actual yield / theoretical yield x 100
maximum amount of product obtained
why can there be a low percentage yield
loss during purification or separation
reaction isn’t completed
other reactions occur simultaneously
Atom economy
efficiency, proportion of reactants converted into desired product
Mr of desired / Mr of total x 100
