2.1.3 Amount Of Substances Flashcards
How many particles/atoms/molecules are in a mole?
6.02 x 10 23
What is the mass of one mole of carbon?
12g
How many atoms in 12g of carbon?
6.02 x 10 23 atoms
What is molar mass Mr measured in
gmol-1 or g/mol
Moles (mol) =
Mass (g)
————
RFM/Mr (g mol-1)
How to work out empirical formula with a given mass or percentage composition by mass
Find the moles by mass / RFM and divide the other moles by the smallest moles to find ratio
How many centimetres/millilitres/litres in 1 dm3?
1000cm3 or 1000ml or 1L
Concentration (mol dm-3) =
Moles(mol)
——————
Volume(dm3)
How to calculate volume (cm3) from moles and concentration
Vol = mol/mol dm-3 = dm3 x 1000 = cm3
How to calculate mass from concentration and volume
Find the moles and fill into moles = mass/rfm
What is the volume of one mole of a gas molecule at room temperature and pressure
24dm3 / 24000cm3
Percentage yield =
Actual yield/ theoretical yield
Atom economy =
Sum of Mr of desired products/ sum of Mr of all products
pV =
pa x m3
nRT
Mol x r x k
How to use ideal gas equation when given density instead of volume and mass
Density = x g dm -3 x grams per 1 dm so our vol is 1 / 1000 for m3 = 0.001
So there are X grams Which can be used to find Mr
How to find rfm using ideal gas equation and a mass
Find moles using ideal gas equation and divide from Mass
What mass of potassium chlorate (V) must be heated to give 1.00 dm3 of oxygen at 20.0ºC and 0.100 MPa.
2 KClO3(s) → 2 KCl(s) + 3 O2(g)
Use gas equation to find moles = 0.0411 of O2
so 2/3 X moles of O2 = moles of KClO3 = 0.0274 X Rfm = 3.36g
K =
C + 273
How to convert from cm3 to m3 and dm3 to m3
Divide by 1 million
Divide by 1000
how to convert from MPa to Pa and KPa to Pa and atm pressure
MPa X 1,000,000 = pa
kPa X 1,000 pa
atm p = 101,000 pa
Gas volume =
Moles x 24dm3 or 24000cm3
Concentration of in mass gdm-3 =
Concentration in mol dm-3 (mols/vol) x RFM
Why isn’t percentage yield 100%?
- Lost due to mechanical transfer
- Loss whilst separating e.g. filtration funnel
- Side reactions(reactants or products react with something unexpected)
- incomplete/reversible reactions
Why are products with higher atom economies better?
They produce a larger proportion of desired products and less unwanted waste products and are important for sustainability as they make the best use of natural resources
How many grams in a ton?
1000000
What is weighted mean mass
Average mass of an atom or molecule taking into account the abundance of isotopes
What does (.xH2O) represent
Water of crystallisation
How do you work out moles of water in a hydrated compound given hydrous and anhydrous masses
Anhydrous mass divided by rfm of anhydrous compound equals = moles
Hydrated mass divided by Moles = RFM
Total RFM - Anhydrous compound RFM = RFM of water
Total Rfm of water divided by 18 = moles
why is C12 used to compare atomic masses
It is the agreed standard
Explain clearly the difference between atom economy and percentage yield
% yield compares the amount produced compared to the amount you should get, atom economy is the proportion
of the mass of all the products that is the desired product
How to find the number of atoms in a molecule
Find the number of moles and X by 6.02× 10 23
What is the apparatus used to measure gas volume produced?
A gas syringe or a conical flask and measuring cylinder
What is the equation for complete combustion?
Fuel + O2 = CO2 + H2O
What assumptions are we making when working out the formula of a hydrated salt?
All of the water has been lost and no further decomposition has occurred
What is made in the ionic equation of acid and hydroxide H+ + OH-
H2O
What is made in the Ionic equation For acid and hydrogen carbonate or carbonate 2H+ + CO3 2- or H+ + HCO3-
Water and Carbon dioxide
What is made in the ionic equation of acid and ammonia H+ + NH3 =
NH4+
density =
mass/volume
Why do we measure multiple times in a water of crystallisation experiment?
To make sure all the water has been removed
How can we reduce percentage uncertainty in a water of crystallisation reaction?
Use a balance that weighs to more decimal places
Use a larger mass of starting reaction
How to get a solid from a sample
Filter to obtain the solid precipitate and then dry or evaporate it
