Chemical changes

Created by

Lorelie

Cards (43)

What is the pH scale  
A measure of how acidic or alkaline a solution is
what has a lower pH
more acidic solutions
what has a higher pH
a more alkaline solution
what pH does a neutral substance have
7
how can you measure pH 
universal indicator
pH probe attached to a pH meter
what is an acid
a substance that forms aqueous solutions with a pH less than 7
acids form h+ ions in water
what is a base
a substance with a pH greater than 7
what is an alkali
a base that dissolves in water to form a solution with a pH greater than 7
alkalis form OH- ions in water
what is the reaction between acids and bases
neutralisation
what is neutralisation
acid + base ———> salt + water
What are titrations used for
To find exactly how much acid is needed to neutralise an alkali
what indicator do you need to use in titrations
a single indicator (litmus, methyl orange, phenolphthalein)
what do acids produce in water
protons
what do strong acids do
ionise completely in water, all acid particles disassociate to release H+ ions
what do weak acids do
do not ionise completely in water, only a small proportion of acid particles disassociate to release H+ ions
how is the ionisation of a weak acid a reversible reaction
it sets up an equilibrium between the disassociated and undissociated acids
why are strong acids more reactive than weak acids  
reactions of acids involve H+ ions reacting with other substances, so if the concerntration of H+ ions is higher the rate of reaction will be faster
what is pH a measure of  
the concentration of H+ ions in the solution
what is acid strength
what proportion of acid molecules ionise in water
what is acid concentration
how much acid there is in a certain volume of water
What are metal oxides and metal hydroxides
Bases
acid + metal oxide 
salt + water
acid + metal hydroxide  
salt + water
Hydrochloric acid 
HCl
Sulfuric acid  
H2SO4
nitric acid 
HNO3
acid + metal carbonate  
salt + water + carbon dioxide
acid + metal  
salt + hydrogen
metal + water  
metal hydroxide + hydrogen
What is an electrolyte
A molten or dissolved ionic compound
what is the cathode 
negative electrode
what is the anode
Positive electrode
Where do the positive ions go  
To the negative electrode where they gain electrons and become the uncharged element
where do the negative ions go
to the positive electrode where they loose electrons and become the uncharged element
why can’t an ionic solid be electrolysed
the ions are in fixed positions and can’t moved
when is electrolysis used to extract metals 
when it’s more reactive than carbon so it can’t be reduced with carbon
why is extracting metals with electrolysis expensive
a lot of energy is required to melt the ore and produce the current
what’s used to lower irons melting point
cryolite
what is present at the cathode in electrolysis of aqueous solutions
H+ and metal ions
what happens if the metal is more reactive than hydrogen
hydrogen gas will be produced