C3 - Amount of substance and the mole Flashcards
What is the Avogadro constant?
N(A)
Number of atoms per mole of the carbon-12 isotope
6.02 x 10^23
What is a mole?
Amount of substance containing as many elementary particles as there are carbon atoms in exactly 12g of the carbon 12 isotope
What is the mass of one mole of any element
Their atomic masses
What is molar mass ?
M
Mass per mole of a substance (g/mol)
Amount of substance formula
Amount (mol) = mass (g) / molar mass (g/mol)
n = m/M
What is molecular formula?
Formula that shows the number and type of each element present in a molecule
What is empirical formula?
Formula that shows the simplest whole number ratio of atoms of each element present in a compound
What does hydrated mean?
Crystalline compound containing water molecules
What is water of crystallisation?
Water molecules that are bonded into a crystalline structure of a compound
What is anhydrous?
Containing no water molecules
How do you calculate formula of a hydrated salt?
Weigh empty crucible
Add hydrated salt into crucible and weigh (hydrated salt)
Using pipe-clay triangle support crucible on tripod
Heat crucible gently for one minute
Then heat strong for three minutes
Leave to cool
Then weigh crucible again (anhydrous salt)
Calculate mole of anhydrous salt
Calculate mole of water
For hydrated salt it’s simplest whole number ratio
What assumptions are made during hydrated salt experiment
1) all water has been lost
-colour change helps but you can only see surface
-better to heat till constant mass
2) no further decomposition
-many salts decompose when heated
1Cm^3 in ml
1 ml
1dm^3 in cm^3
1000
1dm^3 in ml
1000ml
1L
What is concentration?
Amount of solute (moles) dissolved in 1dm^3 of solution
concentration formula
amount (mol) = conc (mol/dm^3) x volume (dm^3)
n = cV
What us a standard solution?
Solution of known concentration
How else can you calculate concentration ?
Using mass
What is molar gas volume?
Vm
Volume per mole of gas molecules at a stated temperature and pressure
What does molar gas volume depend on?
Pressure and temperature
What’s molar gas volume at RTP
24 dm^3
24000cm^3
Molar gas volume rtp formula
Amount (mol) = volume (dm^3) / molar gas volume (dm^3/mol)
n = V / Vm
What are the assumptions made for the molecules making up an ideal gas?
-Random motion
-Elastic collisions
-Negligible size
-No intermolecular forces
What is the ideal gas equation?
pV = nRT
Pressure (Pa) x Volume (m^3) = amount (mol) x Molar gas constant (8.314) x Temperature (K)
What’s ideal gas constant value
8.314 J/mol/K
Units for ideal gas constant equation
Pa
m^3
Mol
K
Cm^3 to m^3
x 10^-6
dm^3 to m^3
x 10^-3
C to K
+273
KPa to Pa
x 10^3
What’s RTP
20C
101kPa
What is stoichiometry
Ratio of the amount of each substance in a chemical equation in moles
What is percentage yield?
( Actual yield / theoretical yield ) x 100%
What’s actual yield
Amount of products obtained form a reaction
What is theoretical yield
Yield from complete conversion of reactants into products
What is the limiting reagent?
Reactant that is not in excess and will be used up first and stop the reaction
What is atom economy
( Sum of molar mass of desired products / sum of molar masses of all products ) x 100
What does atom economy not take into account
Percentage yield
Pollutants
What are the benefits for sustainability of developing chemical processes with high atom economy?
-More efficient so preserve raw resources
-Reduces waste
experimental techniques for molar/ideal gas calculations
add in accordance of exam qs
