chemical changes 4 Flashcards
what is the PH scale
a measure of how acidic or alkaline a solution is
the lower the PH the more acidic
the higher the more alkaline
what is indicator
a dye that changes colour depending on weather it’s above or below a certain PH
some indicators contain a mixture of dys that means they gradually change colour over a broad range of PH
ways to measure PH
PH probe
measure electronically
what is an acid
a susbstance that forms aqueous solutions with PH of less than 7
Acids form H plus ions
what is a base
a substance with a PH level greater than 7
Base(alkali)
base that dissolves in water to form a solution with PH greater than 7
form OH minus ions
acid + base =
salt + water
H plus + OH minus =
H2O
what do reactions of strong acids and alkali help calculate
reactions of a strong acids and alkalis to calculate the concentration by titration
what PH does a neutral substance have
PH 7
what do strong acids do in water
ionise completely in water
all acid particles dissociate to release H plus ions
what do weak acids do in water
do not fully ionise
only a small proportion of particles dissociate to reales H plus ions
what kind of reaction is a weak acid
reversible reaction which sets up an equillibrium between the undissociated and dissociated ions.
lies on the left because only few H plus ions are released
what happens when the concentration of H plus ions increase
rate of reaction will be faster if strong acid
what is the PH of acid or alkali and what happens when the scale decreases
a measure of the concentration of H plus ions
for every decrease of 1 on the PH scale the concentration increases by a factor of 10
general rule when ion concentration changes
factor h plus ion concentration changes by 10-x (x is difference in PH)
what does acid strength tell you
what proportion of the acid molecules ionise in water
what is acid concentration
how much acid there is in a certain volume
metal oxides or metal hydroxide + acid =
salt + water
how you make a salt
metal + acid
acid + metal carbonate =
salt + water + carbon dioxide
what is the reactivity series
lists metals in order of their reactivity
how is metal reactivity measured
how easily they lose there electrons and form positive ions
acid + metal =
salt + hydrogen
how do you measure reactivity
react it with an acid
the speed of the reaction is indicated by the amount of hydrogen gas given off
metal + water =
metal hydroxide + hydrogen
what is a redox reaction
a reaction that separates a metal from it’s oxide
Formation of metal ore =
Oxidation = gain of oxygen
extraction of metal ore =
Reduction = loss of oxygen
how is metal extracted with carbon
by reduction
ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised
how are metals higher than carbon extracted
electrolysis
how are metals below carbon extracted
reduction using carbon
what is oxidation
a loss of electrons
what is reduction
a gain of electrons
OIL RIG
oxidation is loss reduction is gain
what are displacement reactions
involve one metal kicking another one out of it’s compound
rule of displacement reaction
A more reactive metal will displace a less reactive metal
what gains the electrons and what loses the electrons during a displacement reaction
metal ion (reduced) metal atom (oxidised)
what is an ionic equation
only show particles that react and the products produced not the spectator ions
what and how does electrolysis do/work
an electric current is passed through an electrolyte
positive ion in the electrolyte will move towards the cathode and gain electrons
negative ions in the electrolyte will move towards the anode and loses electrons
this creates a flow of charge through the electrolyte as the ions travel to the electrode
why electrolysis only works on molten ionic solids
ionic solid can’t be electrolysised because ions are in a fixed position and don’t move
molten ionic compounds can be electrolysed because the ions can move freely
positive ions are reduced to the element at the cathode
negative ions are oxidised to the element at the anode
how is aluminium extracted using electrolysis
aluminium is extracted from the ore bauxite by electrolysis
aluminium oxide has a very high melting temperature so it’s mixed with cryolite to lower the melting point
The molten mixture contains free ions
the positive 3 plus AL ions are attracted to the negative electrode where they pick up three electrons and turn into neutral aluminium atoms
the negative 2 minus O ions are attracted to the positive electrode where they each lose two electrons
overall equation of extracted aluminium
aluminium oxide = aluminium + oxygen
what do half equations show
show the reactions at the electrodes.
electrolysis of aqueous solutions what else is produced
as well as the ions produced from the compound there will be hydrogen ions and hydroxide ions from the water.
at the cathode if the hydrogen ion is less reactive than the metal hydrogen gas is formed otherwise the metal ion coats the cathode
at the anode if hydroxide ions are present, molecules of chlorine, bromine or iodine will be formed
if no halide ions are present then the hydroxide ions are discharged and oxygen will be formed
reactivity series
potassium k sodium Na lithium Li calcium Ca magnesium Mg carbon C zinc Zn iron Fe hydrogen H copper Cu
