Topic 4 - Chemical Change Flashcards
What is
oxidation/reduction?
Oxidation - When a substance gains oxygen
Reduction - When a substance loses oxygen
What is the reactivity series of
metals? What are the trends in
reactivities of metals in reactions
with acids/water?
The series shows the metals in order of their reactivity.
Metals above H2 in reactivity series react with acid to produce H2. The more reactive the metal is, the quicker and more violent reaction with acid occurs
Metals below H2 don’t react with acids.
Not all metals above H2 react with water - mostly Group I and II metals. Aluminium is the borderline case.
What is a displacement
reaction?
A reaction where a more reactive metal displaces a less reactive metal from a compound
How are unreactive metals
found in Earth?
In their natural state (well, they are unreactive…)
How can metals less
reactive than carbon be
extracted?
Reduction with carbon. Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure metal.
How are metals more reactive
than carbon extracted?
By electrolysis
What is the general equation for a reaction between metals and acids? What type of reaction is this?
Metal + acid → salt + hydrogen
Redox reaction, also a displacement reaction
Which metals in the reactivity
series will react with acid?
Those above hydrogen
What is the general equation for a
neutralisation reaction?
Base + acid → salt + water
What is the general equation for
the reaction between metal
carbonate and acid?
Metal carbonate + acid → salt + water + carbon dioxide
What is the general equation for the reaction between metal oxides and acids?
Metal oxide + acid → a salt + water
How is a soluble salt
formed?
a) React the excess acid with some insoluble chemical (e.g. metal oxide)
b) Filter off the leftovers
c) Crystallise the product
What do acids and alkalis
produce in aqueous solutions?
Acids produce hydrogen ions, alkalis produce hydroxide ions
What are bases, acids and
alkalis?
Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions
What is the pH scale and what
does a pH of 7 show?
The measure of acidity/alkalinity of a solution; neutral solution
State the general equation for a neutralisation reaction in a short, ionic form
H+ + OH− → H2O
Name the following salts:
LiNO3, K2CO3, MgBr2, BaSO4
Lithium nitrate
Potassium carbonate
Magnesium bromide
Barium sulfate
What is electrolysis?
The passing of an electric current through ionic substances that are molten or in solution to break them down into elements; ions are discharged (they lose/gain electrons) at electrodes to produce these
What is an electrolyte?
The liquid/solution which conducts electricity
What is a cathode and what is
an anode?
Cathode is the negative electrode, anode is the positive electrode
What occurs at the cathode and what occurs at the anode
during electrolysis?
Reduction occurs at the cathode
Oxidation occurs at the anode
In aqueous electrolysis, which element is discharged at the
cathode? Oxygen is produced at the anode unless what?
The less reactive element discharges at the cathode. Hydrogen is produced unless there is a less reactive metal, in which case the said metal is produced. Oxygen is produced at the anode unless the solution contains halide ions, in which case halogen molecules are produced.
How is aluminium manufactured?
Why is it expensive?
Aluminium is made through the electrolysis of aluminium oxide and cryolite.
Lots of energy is needed to produce the current in electrolysis which makes this process expensive.
What are the half equations in
the extraction of aluminium?
Al3+ + 3 e− → Al (cathode)
2 O2− → O2 + 4 e− (anode)
Oxygen reacts with C of the anode producing CO2
Why is cryolite used in this
process?
It lowers the melting point of aluminium oxide, reducing energy costs
