1 mole =
atomic mass of any element
eg. 12g of carbon = 1 mole of carbon atoms
6
C
12
what is 1 mole (number)
6.02 x 10*23
number of moles =
mass / Mr (relative formula mass)
relative formula mass, Mr
relative atomic masses of all the atoms in the molecular formula added together
eg. MgCl2
% mass of an element in a compound
(Ar x number of atoms of element) / Mr of the compound
x 100
how could mass increase in a reaction?
one of reactants is a gas
all products are solids, liquids or aqueous
how could mass decrease in a reaction?
one of products is a gas
all reactants are solids, liquids or aqueous
how to work out balanced symbol equation of a reaction
- divide mass of each substance by it’s Mr = moles
- divide number of moles of each substance by smallest number of moles in reaction
- if any numbers are not whole numbers, multiply all numbers by same amount so they become whole numbers
- write balanced equation by putting these numbers in front of chemical formulas
how to work out mass of product formed in reaction
- work out Mr of reactant and product
- work out moles of other substance using it’s given mass
- use balanced equation to work out how many moles are of other substance
- use number of moles to calculate mass
limiting reactant
reactant that gets completely used up in the reaction
concentration (simple)
how crowded things are
concentration =
mass of solute (g) / volume of solvent (dm cubed)
indicator
dye that changes colour depending on it’s pH
how to electronically measure pH
- pH probe
- pH meter
strong acids…
ionise completely in water
all praticles dissociate and release H+ ions
pH is a measure of…
concentration of H+ ions in the solution
weak acids
do not fully ionise in solution
only a small proportion of acid particles dissociate to release H+ ions
redox reaction
electrons transferred
oxidation and reduction take place at the same time
oxidation
addition of oxygen
loss of electrons
reduction
removal of oxygen
gain of electrons
displacement
more reactive element replaces a less reactive element in a compound
spectator ions
elements that do not change in a reaction
eg. symbol equation
Mg + 2Cl- -> Mg2+ + 2Cl-
chloride ions are spectator ions
electrolysis meaning
splitting up with electricity
what happens during electrolysis?
electric current is passed through an electrolyte (molten or dissolved ionic compound)
ions move towards electrodes where they react and compound decomposes
