Chemical Changes Flashcards
Reactivity Series
Potassium
Sodium
Calcium
Maganeiusm
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold
Extracting with carbon
Metals less reactive than carbon can be extracted by it
Oxidation
- loss of electrons
- eg. Na -> Na+ + e-
Reduction
- gain of electrons
- eg. Na+ + e- -> Na
Reaction of acids with metals
- metal + acid -> salt + hydrogen
-> these are redox reactions
Alkali
a substance that dissolves in water to produce hydroxide ions, OH-(aq)
Acid
a substance that dissolves in water to produce hydrogen ions, H+(aq)
Neutralisation of acids
Acids are neutralised by bases and alkalis
- acid + base/alkali -> salt + water
- acid + metal carbonate -> salt + water + carbon dioxide
Ionic equation for neutralisation of acids
H+(aq) + OH–(aq) → H2O(aq)
Letter symbols for different acids
HCl -> forms chlorides
HNO3
H2SO4
H3PO4
pH colours
Acidic -> red (1-6)
Alkaline -> blue (8-14)
Neutral -> green (7)
Strong and weak acids
Strong acid -> completely ionises in solution to form H+ ions
Weak acid -> partially ionises in solution to form H+ ions
The strong an acid the lower the pH
-> dilute acid is a stronger acid than concentrated acid
Electrolysis
A process in which electrical energy, from a direct current supply, breaks down electrolytes
The free moving ions in electrolytes are attracted to the oppositely charged electrodes
Electrolysis of molten ionic compounds
When a simple ionic compound (eg lead bromide) is electrolysed, the metal (lead) is produced at the cathode and the non-metal (bromine) at the anode
Electrolysis of Aluminium Oxide
- has a high melting point and so would be expensive to melt so it is mixed with cryolite to lower the melting point
- the anodes need to be replaced frequently as oxygen is formed which reacts with the carbon of the electrode to form carbon dioxide which burns the electrode
Electrolysis of Aqueous Solutions
At the cathode:
- hydrogen is produced unless the metal is less reactive than hydrogen
At the anode:
- oxygen will be formed unless halide ions are present in which case they will be produced
What colour is phenolphthalein in acids and alkalis
Colourless in acids
Pink in alkalis
What colour is methyl orange in acids and alkalis
Red in acids
Yellow in alkalis
Orange is the endpoint
What colour are acids and alkalis on litmus
Red in acids
Blue in alkali
Bases
Substances that neutralise acids
(Metal oxides, metal carbonates, alkalis, ammonias)
