Chem Unit 1 (Amount of substance) Flashcards
Relative atomic mass
average mass of an atom of an element/ 1/12 of a mass of carbon-12
Number of protons and neutrons added together
Relative molecular mass
average mass of a molecule/ 1/12 of the mass of an atom of carbon-12
add together the number of atoms in each element in a molecule
Relative formula mass
mass of the formula unit (ratio of each type of atom in a lattice)
adding the number of atoms of each element in the lattice
Avogadro’s constant
number of atoms in 12g of carbon-12
6.023 x 10 23
a mole of particles contains 6.023 x 10 23 particles.
How do you use Avogadro’s constant?
To work out the number of moles of a substance you times the mass of a single atom x Avogadro’s constant.
How do you work out the mass of a single atom?
Example: 1 H - You would add together 1 proton and 1 electron
1 H + - You would add together 2 protons
3 H - You would add 2 neutrons and 1 proton
If it just asks yo to work out the MASS you don’t need to times by the Avogadro’s constant next.
If it gives you Mr moles = mass / Mr
Empirical formula
Simplest whole number ratio of atoms of each element in a compound.
Molecular formula
Actual number of atoms of each element in a compound.
How do you work empirical and molecular formula out?
Empirical: Divide % or given mass by atomic mass
Divide by smallest number to get simplest ratio
Molecular: Divide Mr of whole thing (given) by the Mr of empirical formula (Atomic masses of each of the elements in the compound.
What is percentage yield?
actual yield / theoretical yield x 100
How do you work out % yield?
Theoretical mass: Mr of reactants
moles = mass/Mr [DON’T RATIO HERE]
ratio out moles for products
Mass = moles x Mr of products
Actual yield (given) / Your theoretical yield x 100
Reasons why it was less: reversible reactants in impurities
What is atom economy?
mass of desired products / total mass of reactants x 100
How do you work out atom economy?
No given numbers
Divide the Mr of the desired product / Mr of ALL THE REACTANTS x 100
NO RATIO
If there is only one product…
The atom economy must be OVER 100%
Why is a higher atom economy better?
- less disposable cost
- less waste
- cheaper to manufacture
What are isotopes?
Atoms of the same element with the same number of protons but a different number of neutrons.
Chemical and physical properties of isotopes?
Chemical: same because the arrangement of electrons are the same.
Physical: Different because the mass will slightly vary.
% isotopic abundance?
The % of each isotope that naturally occurs o earth
Different in space- different %’s (isotopic signature)
Values in data book and mass spec data is going to be different because the % isotopic abundance is going to be different.
Ideal Gas properties and realistic?
Particles are constantly in motion
They’re constantly colliding
These collisions don’t produce reactions
Kinetic energy is conserved
No intermolecular forces that divert their path range.
Real gasses DO have intermolecular forces that divert the path of particles.
Some can act like ideal gasses under limited temperature and pressure ranges.
Idea; Gas Equation?
pv = nRT
Conversions for cm3, dm3> m3?
cm3 x 10-3 = dm3
dm3 x 10-3 = m3
cm3 x 10-6 = m3
Conversions for degrees>kelvin
kPa/Mpa>Pa
Degrees + 273 = K
kPa x 10-3 = Pa
mPa x 10-6 Pa
To work out Mr for ideal gas equation?
n = PV/RT
n (moles) = mass/Mr
Mr = moles / mass
How do you work out concentration?
conc = moles/ vol
