C4 - calculations Flashcards
what is a mole
mass of a substance that contains 6.02x10^23
give the value for Avogadro’s constant
6.02x10^23
which formula is used to calculate the number of moles from mass and Mr
mass = moles x Mr
what is a limiting reactant
the reactant that is completely used up in a chemical reaction
what is a unit for concentration
g/dm3 or mol/dm3
which formula is used to calculate concentration from mass and volume
volume(g/dm3) = mass(g)/ volume(dm3)
how can you convert a volume reading in cm3 to dm3
divide by 1000
if the amount of solute in a solution is increased, what happens to it’s concentration
increases
if the volume of water in a solution is increased what happens to the concentration
decreases
what is the yield of a reaction
mass of product obtained from the reaction
what is the theoretical yield of a reaction
maximum mass of the product that could have been produced
why is the actual yield always less than the theoretical yield
- reaction may be reversible
- some of the product can be lost on separation
- unexpected side reactions between reactants
what is the percentage yield
actual yield as a proportion of theoretical yield
how is percentage yield calculated
actual yield
—————— x 100
theoretical yield
what is atom economy
measure of how many atoms of the reactants end up as useful products
why is a high atom economy desirable
results in less waste/is more sustainalble
how is percentage atom economy calculated
Mr of useful product
—————————— x 100
Mr of all reactants
how can the concentration in mol/dm3 be calculated
moles of solute/
volume
what is titration
method used to calculate the concentration of an unknown solution
what is the end-point
the point at which the reaction is complete (when the indicator changes colour) and no substance is in excess
how should solution be added from the burette close to the end point
drop by drop, swirling in between
why is a white tile used in titration
to see the colour change better
what is a titre
volume of solution added from the burette
what does one mole of any gas occupy at room tempereature and pressure
24dm3 or 24000cm2
how to work out the Mr
the sum of the relative atomic masses of the atoms in the numbers shown in the formula. Relative formula mass (Mr) of CaCO3 = 40+12+(3x16)=100.
how to work out the Ar
relative atomic mass = (abundance of isotope 1 × mass of isotope 1 ) +
(abundance of isotope 2 × mass of isotope 2)
/100
