2.1.3 Amount of substances Flashcards
the mole is…
the amount of substance in grams that has the same number of particles as there are atoms in 12g of carbon 12
relative atomic mass is…
the average mass of an atom compared to the mass of one atom of carbon 12
relative molecular mass is …
the average mass of a molecule compared to one twelfth of the mass of one atom of carbon 12
molar mass is…
the mass in grams of one mole of substance (gmol-1)
avogadro’s constant
the number of particles in one mole
mass =
n x Mr
no of particles =
n x 6.02 x 10^23
volume in (dm^3)
n/C
moldm^-3 can be made into gdm^-3 by…
multiplying by the Mr
avogadro’s number shows …
that there are 6.02 x 10^23 atoms in 12g of carbon 12
xH2O means …
water of crystallisation
salts that have water removed are …
anhydrous
empirical formula is…
the simplest whole number ratio of atoms in a compound
molecular formula is …
the actual number of atoms in a compound
how to work out the factor of an empirical formula
factor = mr of molecular formula / mr of empirical formula
to work out the molecular formula you …
empirical formula x factor
ideal gas equation
P(Pa)V = nRT
T=
273 +/- ?°C
R =
8.31
V (m^3) =
cm^3 / 10^6
or
dm^3 / 1000
1 mole of any gas at room temp and room pressure =
25°C and 24dm^3
gas volume (dm^3) =
n x 24 (or 24,000 if answer is wanted in cm^3)
% yield =
actual yield / theoretical yield x 100
name two ways % yield can be lowered
- incomplete reactions
- side reactions
- losses during purification
- transfer of substances
% atom economy =
mr or mass of useful products / mr or mass of all reactants x 100
name two potential errors when using a gas syringe
- gas escapes before bung is inserted
- syringe sticks
- some gases are soluble so the true amount of gas may not be measured
method for titration
1) rinse equipment with distilled water
2) using a pipette put 25cm^3 of alkali into a conical flask and add a few drops of indicator
3) fill burette with acid up to 0 and place flask on top of a white tile underneath the burette
4) add acid whilst swirling flask until colour change is seen and record in a table
5) repeat until two concordance results occur
why is a conical flask used instead of a beaker ?
so contents is less likely to be spilled
only small amounts of indicator are added because…
they are weak acids so too much would affect the result
when working out the average titre you use…
the two concordant results
% error =
+/- sensitivity error/ measurement made on apparatus x100
name two ways to decrease apparatus errors
- decrease the sensitivity error by using apparatus with a greater resolution
- increase the size of the measurement made
