Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chemistry Topic 4 Chemical Changes, Reactivity Series ADDED, titration,…
Chemistry Topic 4 Chemical Changes
Reactivity of Metals
The Reactivity Series
Metals form positive ions when they react and reactivity is based on how likely a metal is to form positive ions. Therefore the reactivity series has the most reactive metal at the top.
Carbon and Hydrogen
aren't metals but are included in the reactivity series as they can be used to extract metals from their ores, depending on their reactivity.
Displacement
A more reactive metal can displace a less reactive metal from a compound.
Silver nitrate + sodium chloride ------- Silver Chloride + Sodium Nitrate
Group 1
metals react more vigorously with water and acid the further down the group.
Group 2
metals do not react with water but will fizz and get hotter when reacted with acid.
Zinc, iron and copper
do not react with water but zinc and iron will react slowly with acid but copper won't.
Metal Oxides
Metal and oxygen
- Metal reacts with oxygen to form metal oxides.
Reduction
This is when oxygen is removed from a compound in a reaction.
Oxidation
This is when oxygen is gained by a compound.
Oxidation and Reduction in terms of Electrons
Oxidation
is
Loss
of electrons.
Reduction
is
Gain
of electrons.
Ionic Half Equations
(displacement reactions) Ionic equations show what happened to each other reactants.
The half-equation for iron (II) is:
Fe → Fe2+ + 2e-
Reactivity of Acids
Neutralisation of Acids and Salt Production
Hydrochloric acid turns to chloride.
Sulfuric acid turns to sulfate.
Nitric acid turns to nitrate.
Neutralisation
: Acids can be neutralised by alkalis or bases. An
alkali
is a soluble base e.g. metal hydroxide. An
base
is a substance that neutralises an acid e.g. soluble metal hydroxide or a metal oxide.
Reactions of Acids and Metals
Acids react with some metals to make salts and hydrogen.
metal+ acid------ metal salt+ hydrogen
Reactions between metals and acids are redox reactions because the metal donates electrons to the hydrogen ions. This displaces hydrogen as a gas while the metal ions are left in the solution.
The pH scale and Neutralisation
Acids produce hydrogen ions (H+) in aqueous solutions.
Aqueous solutions of alkalis contain hydroxide ions (H-).
In
neutralisation
reactions, hydrogen ions react with hydroxide ions to produce water: H+ + OH- → H2O
You can use universal indicator to measure the acidity or alkalinity of a solution against a pH scale.
Soluble Salts
Can be made from mixing acids with solid insoluble substances like metals.
To make them add the solid to the acid until no more dissolves. Filter off excess solid and crystalize to produce solid salts.
Strong and Weak Acids
Strong acids
are completely ionised in aqueous solution e.g. hydrochloric acid.
Weak acids
only partially ionise in aqueous solutions e.g. ethanoic acid
Hydrogen ion concentration
As the pH decreases by one unit, the hydrogen ion concentration increases by a factor of 10.
Extraction of Metals
Extraction Using Carbon
Metals less reactive can be extracted from their oxides by reduction.
E.g.
zinc oxide + carbon ------- zinc + carbon dioxide
Unreactive metals like gold are found in the Earth by itself. These can be mined.
Titrations
Method
1.
Use the pipette to add 25cm3 of alkali to a conical flask and add a few drops of indicator.
2.
Fill the burette with acid and note the starting volume. Slowly add the acid from the burette to alkali in the conical flask, swirling to mix.
3.
Stop adding acid when the end-point is reached (appropriate colour change). Note the final volume reading. Repeat till there's consistent readings.
Titrations are used to find a very specific volumes of acid that react with alkali solutions.
Electrolysis
Electrolysis of Aqueous Solutions
At positive electrode
Oxygen is formed. If you have a halide ion (chlorine, iodine or bromine) then you will get chlorine bromine or iodine formed at hat electrode.
At negative electrode
Metal will be produced if its less reactive then hydrogen. Hydrogen will be produced if the metal is more reactive then hydrogen.
The process of electrolysis
is: When an ionic compound is melted or dissolved in water, then the ions are free to move. These are then able to conduct electricity and are called electrolytes. Passing electricity through electrolytes cause the ions to move to electrodes.
Electrodes
Anode
is a positive electrode.
Cathode
is a negative electrode.
Ions
Anion
is a negative ion and they move to an anode.
Cations
are positive ions that move to cathodes.
Extracting Metals using Electrolysis
Metals can be extracted from molten compounds using electrolysis.
This is used when the metal is too reactive to be extracted by reduction with carbon.
It's a very expensive method because it requires huge amounts of energy to supply the electric current. e.g. aluminium is extracted via electrolysis.
You can display what is happening with both electrodes using half equations:
At the cathode: Pb2+ + 2e- → Pb
At the anode: 2Br- → Br2 + 2e-
