Relative Mass and Amount of Substance Flashcards
What is Ar?
Relative atomic mass
What does Ar use?
Elements only
Define relative atomic mass
The average mass of an element relative to one twelth of the mass of an atom of carbon-12
What is carbon-12 used in Ar?
It is highly abundant and the twelve has very little rounding therefore it is highly accurate
What are isotopes?
Atoms with the same number of protons but a different number of neutrons
How is Ar calculated?
The sum of (the individual mass of each isotope multiplied by their percentage abundance) divided by the sum of the percentage abundances
What are the units for Ar?
grams per mol
Define relative molecular mass
The mass of a molecule relative to one twelfth the mass of an atom of carbon-12
What is Mr used for?
Simple covalent molecules and diatomic molecules
What are the Mr units?
Grams per mole
How is Mr calculated?
It is the sum of the Ar values of the elements in the molecule
What is the relative formula mass?
The mass of the formula, relative to one twelfth the mass of an atom of carbon-12
What is RFM used for?
Giant ionic compounds (salts)
What is the mole?
A measure of an amount of a substance and the number of atoms in 12g of carbon - 12
What is Avogadros constant
6.02 x 10^23 molecules or atoms in one moles
How do you calculate the number of moles?
Number of atoms/molecules divided by avogadros constant
How do you calculate the number of atoms or molecules?
The number of moles x avogadros constant
How do you calculate avogadros constant?
The number of atoms or molecules divided by the number of moles
What is molar mass?
Ar/Mr and RFM
What are the molar mass units?
Grams per mole
How do you calculate the number of moles?
Mass (g) divided by molar mass
What is the water of crystallisation?
The amount of water relative to one mole of salt
How is the water of crystallisation calculated?
Find the number of moles of salt and water and divide by the smallest to give the ratio
What are the units of concentration?
Mol.dm^-3
What are the units of volume?
dm^-3
How do you convert between cm and dm?
- Divide cm by 1000 to give dm- 1 dm = 1000 cm
What is the equation for the mole and solutions?
Number of moles = Concentration x Volume
How many dm^3 does 1 mole of gas occupy?
24
How many cm^3 does 1 mole of gas occupy?
24000
How can volume of gas be calculated?
Volume of gas (dm^3) = moles x 24 (dm^3)
What are the key assumptions the ideal gas equation makes?
- No IMF between gas molecules- Volume occupied by gas molecules is negligible
What is the ideal gas equation?
Pv=nRT
In the idea gas equation, what is p?
Pressure
In the idea gas equation, what is v?
Volume
In the idea gas equation, what is n?
Moles
In the idea gas equation, what is r?
Ideal gas constant
In the idea gas equation, what is t?
Temperature
In the idea gas equation, what are the units of p?
pa or nm^-2
In the idea gas equation, what are the units of v?
m^3
In the idea gas equation, what are the units of n?
There are none
In the idea gas equation, what are the units of r?
J.K^-1.Mol^-1
In the idea gas equation, what are the units of t?
Kelvin
How can you convert between pa and kpa?
pa = kpa x 1000
How can you convert between m^3 and cm^3
m^3 = cm^3 x 10^-6
How can you convert between m^3 and dm^3
m^3 = dm^3 x 10^-3
What is the ideal gas constant?
8.314
How can you convert between degrees celcius and kelvin?
+ 273 to degrees celcius to get kelvin
What is the % by mass equation?
(Ar of 1 mole of the element) / (Mr/RFM) all multiplied by 100
What is the empirical formula?
The simplest whole number ratio of elements in a compound
What can the empirical formula be calculated from?
%mass or mass
How is the empirical formula calculated?
- %mass or mass / Ar- All Ar’s / smallest Ar to give ratio
What is the molecular formula?
The actual number of atoms of each element in each molecule of a substance
What is the only way of calculating molecular formula from empirical formula?
Using Mr
How is the ratio of empirical to molecular formula calculated?
Mr/ Empirical Mr
What is the atom economy?
The efficiency of a reaction
How is % atom economy calculated?
Total molar mass of desired products divided by the total molar mass of reactants all multiplied by 100
Why is a higher atom economy desirable?
There are less waste products which could be harmful to the environment or expensive to dispose of therefore a higher atom economy will be industrially more economic and safer to the environment
How is percentage yield calculated?
Actual yield / theoretical yield
