C4 chemical changes Flashcards
Oxidation
Metal gains oxygen
Loses electrons to make positive ions
Electrons transferred to oxygen atom to make negative ions
Basic oxide formed
Reduction
Loses oxygen
Gains electrons
Most abundant element in earths crust
Oxygen
Silicon
Aluminium oxide
Iron 3 oxide
Reactivity with water and dilute acids
Potassium Sodium Lithium Calcium Magnesium Zinc Iron Copper
Positive ions
First 8 in reactivity series form positive ions
The harder it is to from a positive ion the more reactive it is
Reactivity series
Potassium Sodium Calcium Magnesium Aluminium Carbon Zinc Iron Tin Lead Hydrogen Copper Silver Gold Platinum
Displacement reaction
When 2 metals react the more reactive metal displaces/ pushes out the less reactive metal
Reduction uses
Used to extract metals from their ores
Ores
A naturally occurring solid material from which a metal or valuable mineral can be extracted profitably by electrolysis
Making salts
Acids react with metals to produce salts and hydrogen
To make a crystallised salt
Add excess of substance to acid
Solution needs to be filtered into a crystallising dish
Solution needs to be concentrated by evaporation
Solution then left to evaporate, to crystallise
Redox reaction
Both oxidation and reduction occur at the same time
Bases
Metal oxides and metal hydroxides
If solvable in water alkalis
Lower concentration of H+ ions
Neutralisation
Acid+base}salt+water
Required practical- preparing a pure,dry sample of a soluble salt from an insoluble oxide or carbonate
Warm up some acid
Put in powdered metal/base in excess
Filter solution into evaporating dish
Heat till it starts to spit then leave to evaporate and crystallise
Acids
Substances that produce hydrogen ions in aqueous solution
Higher concentration of H+ ions lower concentration
Required practical- finding the reacting volumes of solutions of acid and alkali by titration
Acid in burette
Alkali in pipette to conical flask
Indicator in flask with alkali
Slowly add acid to alkali till indicator changes colour.
Record and try to match result within 0.1
Can find concentration
Strong acid
In water all of the acid molecules,HA, become ions (H+ and A-)
Ionise completely in water
Weak acid
In water on,y a few of the acid molecules become ions, most stay as molecules
Do not ionise fully
Equilibrium lies to the left
High concentration of H+
pH is low
Low concentration of H+
pH is high
Titration curve
Rapid fall of pH to the start with, but then slows down
All the alkali is neutralised
Excess acid, pH is below 7
Electrolysis
The process of passing direct current through a solution or melted ionic compound to move the ions apart and so break the compound down and discharge some of the elements at the electrodes
Electrolyte
The solution or molten compound
Ions need to be free to move around
Cathode
Negative electrode
Electrons are gained
Anode
Positive electrode
Electrons are given up
Cations
Positive ions attracted to the cathode
Anions
Negative ions are attracted to the anode
Ions discharging
All ions migrate towards 2 electrodes
Positive to cathode
Negative to anode
Simple binary electrolyte
Made up of 2 ions
Eg. Lead bromine or copper chloride
Can conduct electricity if melted
Preferential discharge
Based on reactivity series
The relatively least reactive ions are preferentially discharged as elements
Required practical- investigating what happens when aqueous solutions are electrolysed using inert electrodes
Circuit- battery, 2 electrodes
Anode- Cl2, OH-
Cathode- Mg, H+,
Discharged- oxygen and hydrogen
