Moles 1 - Solids Flashcards
what is the mole (mol)
mole (mol) is the unit of measurement for substances. It always contains the same number of particles
Avogadro constant
The Avogadro constant is the number of entities in one mole of a substance
L, (6.02 × 10^23 mol-1)
Molar mass
Molar mass of a substance is the mass per mole of the substance (basically atomic mass)
in g mol-1
Multiply the atomic weight of each element with its number of atoms present in the compound
e.g H2O = 2x1 + 1x16 = 18
Empirical formula
The simplest whole number ratio of the atoms of each element in the substance
Molecular formula
shows the number of atoms of each element in one mole of the substance
Relative atomic mass (Ar) definition
The mean mass of an atom of an element, compared to 1/12th of the mean mass of an atom of the carbon-12 isotope
Relative molecular mass (Mr) definition
The mean mass of a molecule of a compound, compared to 1/12th of the mean mass of an atom of the carbon-12 isotope
What is term used instead of relative atomic mass (Ar) for iconic compounds?
Relative formula mass (Mr)
How to find the number of particles present in a sample with know mass
Number of particles = amount of substance (mol) * avogradro constant
Number of particles = nL
n = moles
L = avogadro constant (6.022/23 x 10^23)
How to find the number of ions present in a sample with know mass
Number of ions = amount of substance (mol) * avogradro constant * number of ions
Number of particles = nL x number of ions
ex - MgCl2 = Mg^2+ & Cl^- = 3 ions
n = moles
L = avogadro constant (6.022/23 x 10^23)
How to find the number of atoms present in a sample with know mass
Number of particles = amount of substance (mol) * avogradro constant * atoms
Number of particles = nL x atoms
ex - atoms in N2O4 = 6 (2+4)
n = moles
L = avogadro constant (6.022/23 x 10^23)
How to find the number of electrons present in a sample with know mass
Number of particles = amount of substance (mol) * avogradro constant * electrons
Number of particles = nL x electrons
n = moles
L = avogadro constant (6.022/23 x 10^23)
How to find amount of substance (moles) in solids
In solids
Number of moles = mass(g)/ Mr or Ar (g/mol)
working out concentration in moldm^-3
In solutions
Concentration (moldm^-3) = amount of substance (mol) / volume (dm^3)
working out concentration in gdm^-3
In solutions
Concentration (gdm^-3) = mass of substance (g) / volume (dm^3)
cm^3 —> dm^3
and
dm^3 —> cm^3
cm^3 / 1000 = dm^3
dm^3 x 1000 = cm^3
How to find the empirical formula of a substance
1) write out the elements involved
2) write out the percentages as masses
3) divide these by relative atomic mass to get number of moles
4) divide all numbers by the smallest number of moles to get whole number ratio
5) to find molecular formula, work out Mr of empirical and divide it by Mr of molecular, multiply this by all the atoms in the empirical
How to find the empirical formula of hydrocarbon combustion components
1) write out the products (eg H2O and CO2) as headings
2) write the masses of each molecule
3) divide these by the relative molecular mass to get number of moles
4) multiply by the amount of atoms in a molecule (ex for H20 H = 2, so multiply by 2)
5) divide number of atoms (eg C+H) by the smallest number of moles to get the smallest whole number ratio.
Ionic equations
Ionic equations show the ions that are formed in solutions and show which particles are reacting
1) split all aqueous components (acids, alkalis, salts)
2) cancel ions that appear on both sides of the equation (spectator ions - they don’t get involved in the recation) to form the simplest ionic equation
3) in the final equation the charges must balance on the left & right of the equation
Using chemical equations to work out masses/volumes/concentrations of reactants/products involved in a reaction
1) using info given, find moles
2) find ratio of moles you have to moles of desired thing
3) work out needed thing from moles
