Moles Flashcards
Mole
The amount of substance that contains the same number of particles that 12g of carbon 12 has of atoms
Avogadros constant
Number of atoms in exactly 12g of carbon 12
Which is 6.022x10²³
What is the molar mass of a substance?
The mass of one mole of that substance
Which is the same value as the Ar or Mr
Expressed in gmol⁻¹
Why do we use moles?
As a form of counting the amount of atoms in a substance
Which to do would be impossible and use very big numbers
So use this idea of moles to scale up and therefore use numbers easier to deal with
How to find number of moles from mass?
Mass
———
Mr/ Ar
What can moles be made up of?
Anything, such as atoms, ions, molecules, electrons
How do you find the number of atoms in a substance when given the mass of it?
Find number of moles of it by doing mass/Mr or Ar
Multiply the number of moles by avogadros constant
What represents avogadros constant?
L
Formula for number of atoms/molecules/ions etc
Avogadros constant x number of moles
How to find the mass of a specific number of atoms/molecules/ions etc?
Divide the number of particles by avogadros constant to find the number of moles
Multiply that by the Mr/Ar to find the mass
What to remember when writing equations?
Make sure they are balanced (can use fractions as big numbers)
Use state symbols if necessary
Determine whether reaction is reversible or not
Ionic equations
An equation which shows any atom/ molecules involved
But only the ions that react together
And no spectator ions
Spectator ions
Ions that are there before and after the reaction but are not involved in the reaction
How to write ionic equations?
1) Replace all the compounds/elements as ions
leave molecules eg co2 as is
2) cross out identical ions (spectator ions) on both side
3) rewrite to be only remaining ions left and as aqueous
Remaining ions in an ionic equation
Ions that reacted with each other to form a New Ionic compound
And existed as something else before reaction
When might there be no ionic equation?
If all the products and reactants are aqueos then there is no change in ions charge/bonding so no ionic equation
Ionic half equation
A type of reaction that involves only one reactant and shows the gain or loss of electrons from it
When are ionic half equations written?
Involving oxidation or reduction
Reacting masses according to ratio (no moles included)
If the molar ratio is given when can see the ratio of products to reactants
Then if given the mass of 1 mole can work out the masses of the other species given the ratio
How can we use reacting masses to determine the ratio the reactants react in thus the equation?
Calculate the number of moles using information given
Simply this to simplest whole number ratio
When might we need to use reacting masses to find the equation of a reaction
When a salt exists as hydrates where we aren’t sure of the number before which therefore may affect the equation.
Hydrate
A compound that contains water of crystallisation
Molar mass/Mr of a hydrate
Normally calculate the mr of the compound then multiply the mr of water by how many are present in the hydrate
