5. formulae, equations and amounr of subtance (as) Flashcards
what is a mole
a unit for amount of a substance
6.02 x 10^23 what does that represent
what are the number of particles in one molecule (avogadros constant )
molar mass def
(MR) mass per mole of something
number of moles =
mass of substance/ molar mass
concentration of a solution def + unit
how many moles are dissolves per 1 dm^3
mol/dm3
number of moles = from con
concentration (mol/dm3) x volume (dm3)
mass of substance = from con
concentration (g/dm3) x volume (dm3)
concentration of solution second measurement
how many grams of a substance are dissolves per 1dm3 of the solution g/dm3
empirical formula def
smallest whole no ration of atoms of each element in a compound
molecular formula def
the actual number of atoms of each type of element in a molecule
empirical formula calculated
ex
4.4g of co2 1.8g of water made empirical formula of hydrocarbon
no of moles of co2- mass/ mr = 0.10
no moles of hydrogen- mass/ mr 0.20
ratio
c:h 1:2 ,, ch2
balanced equation def
same number of each atom on both sides
state symbols show
state of matter of things are in
state symbols
solid s
liquid l
gas g
aqueous ( solution in water) aq
displacement reaction
a more reactive element reacts to take the place of a less reactive element in a compound
base reacts with acids
salt and water produced sometimes co2
under the same condition
gases take up the same volume
molar gas volume def + unit
the space that one mole of gas occupies at a certain temp or pressure dm3/mol
24dm3/mol at what temp and pressure
room temp + pressure
rtp- 293k
20 celsius
101.3 kpa
standard temp and pressure stp the molar gas volume 22.4 dm3/mol
stp 273 k
0 celsius
101.3kpa
number of moles from molar gas
volume (dm3)/ molar gas volume
how to measure molar volume of a gas
- find vol of gas by collecting gas that’s produced in gas syringe or by displacing water from a measuring cylinder
ideal gas equation
pv = nrt
p= pressure (pa)
v=volume (m3)
n=number of moles
r= 8.31j/k/mol
t= temp (k)
kelvins calculate
celsius + 273
molar mass of an unknown volatile liquid how to calculate
put a known mass of liquid into a flask
attach to sealed gas syringe
warm gently in water bath
until liquid evaporates
record volume of gas in syringe and temp of water bath
use ideal gas equation to work out how many moles of liquid were in sample
molar mass = from moles
mass/moles
titrations used
to find a conc of acid or alkali solutions
hazard def + risk associated w it
anything that has the potential to cause harm or damage
probability of someone being harmed if they’re exposed to hazard
risk assessment
identifying all hazard + risk of it and how likely it is that something could go wrong and how serious it is if it did and ways to reduce risk
standard solution
has known concentration
how to make a standard solution
Woke out how many moles of solute you need mol=con x vol/1000
how many grams of solute needed mass = moles x molar mass
weigh out mass of solute using a balance weigh first weighing vessel
add solid acid to beaker add 100cm3 of distilled water and stir until solute dissolved
reweigh weighing vessel to see how much had been added
tip solution into volumetric flask
rinse beaker and stirring rod w distilled water and add that to the flask too
add more distilled water to line
stopper the bottle and turn upside down a few times to make sure it’s all mixed
methyl orange
turns yellow red
when adding acid to alkali
phenolphthalein
red to colourless when adding acid to alkali
titration show
how much acid needed to neutralise a quantity of alkali
acid base titration steps
measure alkali of unknown conc
add indicator
rinse burette w standard solution of acid then fill it w standard solution
do a rough titration
then an accurate one
swirl
work out amount of acid used to neutralise the alkali (final reading - initial reading) volume = titre
repeat until concordat results
pipette
measures only one volume of solution
burette
measures different volumes and lets you add the solution drop by drop
uncertainty
amount of error your measurements might have
any measurements you make have uncertainty in them due to
the limits to then sensitivity of the equipment used
what does the +- sign tell you in uncertainty
the range in which the true value could lie called the margin of error
uncertainty calculate
calculate range /2
percentage uncertainty
uncertainty/ reading x 100
ways to minimise percentage uncertainty
use the most precise equipment you can
plan to improve your results
errors can be
systematic or random
systematic errors
can be the same very time you repeat the experiment
could be by the way you set up the equipment
random error
be different each time you repeat the experiment
repeating experiment and finding mean of results
helps deal with random errors but won’t help systematic errors be more accurate
kpa to pa
x 10^3
cm^3 to m^3
x10^-6 or divide by 10^6
dm^3 to m^3
divide by 10^3 or x10^-3
celcius to k
add 273
percentage yield
actual yield / theoretical yield x 100
atom economy
molar mass of desired products/ sum of molar masses of all products x 100
