3.1.2 - amount of substance Flashcards
roughly how many particles is one mole
6.02 * 10^23 (Avogadro constant)
how is amount of substance measured?
using the mole (mol for short)
what symbol is usually given to moles
n
number of particles equation
number of particles =
number of moles * Avogadro’s constant
mass and Mr
1 mole of any substance has the mass of its relative molecular mass (Mr)
moles/mass/Mr equation
moles = mass / Mr
what number is Mr on the periodic table?
the larger number
define the concentration of a solution?
concentration of a solution is how many moles are dissolved per 1 dm^3 of solution
units of concentration
mol dm^-3
moles/concentration/volume
moles = concentration * volume
dm^3 to cm^3
multiply by 1000
dm to cm
multiply by 10
ideal gas equation
pV = nRT
ideal gas equation
p
pressure
measured in pascals (Pa)
ideal gas equation
V
volume
measured in m^3
ideal gas equation
n
number of moles
ideal gas equation
R
gas constant
8.31 J K^-1 mol^-1
ideal gas equation
T
temperature
measured in Kelvin (K)
kPa to Pa
multiply by 1000
degrees Celsius to Kelvin
add 273
cm^3 to m^
multiply by 10^-6
dm^3 to m^3
multiply by 10^-3
what is the Avogadro constant
number of particles in a mole
what is empirical formula
simplest whole number ratio of atoms of each element in a compound
what is molecular formula
actual number of atoms of each element in a compound
state symbols:
S
solid
state symbols:
L
liquid
state symbols:
G
gas
state symbols:
Aq
aqueous (solution in water)
neutralisation reaction
when acid reacts with an alkali you get a salt and water
what is a standard solution?
a solution you know the exact concentration of
what does making a standard solution involve?
dissolving a known amount of solid in a known amount of water to create a known concentration
making a standard solution
step 1
calculate number of moles and mass of substance you need
making a standard solution
step 2
place weighing bottle on digital balance and weigh out the required mass of the solid approximately and tip it into a beaker
making a standard solution
step 3
weigh the weighing bottle. subtract mass of the bottle from the mass of the bottle and solid together to find the mass of the solid you weighed out
making a standard solution
step 4
Add distilled water to the beaker and stir till all the solid has dissolved
making a standard solution
step 5
tip solution into a volumetric flask of the correct volume using a funnel
making a standard solution
step 6
rinse beaker/stirring rod/funnel with distilled water and add this to the beaker. makes there is no solute clinging to any of the equipment
making a standard solution
step 7
top up flask to correct volume with distilled water. make sure bottom of the meniscus reaches the line. when you get close to the line add water drop by drop
making a standard solution
step 8
stopper the flask and invert it a few times so it is mixed well
making a standard solution
step 9
calculate the exact concentration of your standard solution
what do titrations allow you to find
how much acid is needed to neutralise a measured quantity of alkali (or vice versa)
performing a titration
step 1
use a pipette to measure out set volume of solution that you want to know the concentration of. put it in a flask
performing a titration
step 2
add a few drops of an appropriate indicator to the flask
performing a titration
step 3
fill a burette with a standard solution of the acid (you know its exact concentration)
performing a titration
step 4
use a funnel to carefully pour the acid into the burette (below eye level to avoid acid getting on your face/eyes)
performing a titration
step 5
do a rough titration first to get an idea where the end point is (point where alkali is neutralised and indicator changes colour)
performing a titration
step 6
take an initial reading of how much acid is in the burette. gradually add acid to alkali, regularly swirling the flask. when colour changes take a final reading
performing a titration
step 7
next do an accurate titration
performing a titration
step 8
take an initial reading then run the acid in to within 2cm^3 of the end point. when you get to this stage, add it dropwise
performing a titration
step 9
find the amount of acid needed to neutralise the alkali by subtracting the final reading from the initial reading (titre)
performing a titration
step 10
repeat titration until you have at least 3 concordant results then calculate the mean titre
what colour is methyl orange in acids
red
what colour is methyl orange in alkalis
yellow
what colour is phenolphthalein in acids?
colourless
what colour is phenolphthalein in alkalis?
pink
how do you calculate volume
volume =
number of moles / concentration
what is theoretical yield?
mass of the product that should be formed in a chemical reaction
what is actual yield?
actual mass of product formed in a chemical reaction
why is actual yield less than theoretical yield?
- not all starting chemicals react fully
- side reactions
- incomplete reactions
percentage yield calculation
(actual yield / theoretical yield) *100
define atom economy
measure of the proportion of reactant atoms that become part of the desired product in the balanced chemical equation
what benefits do reactions with a high atom economy have?
environmental, economic and ethical
economic advantages of a high atom economy
- more efficient use of its raw materials
- less waste to deal with so spend less on separating desired products and waste products and waste products produced need to be disposed of safely
environmental/ethical advantages of a high atom economy
-use fewer raw materials/produce less waste
- waste chemicals often harm environment
- cheaper process means products sold for lower prices/available to more people
percentage atom economy equation
(molecular mass of desired product /
sum of molecular masses of all reactants)
* 100
