Post on 01-Jan-2016
description
Making Changes
Topic overview
The topic can be conveniently split into six interrelated sections
Oxidation/Reduction
Salts
Preparation of gases
Metal extraction
Reactions of carbonates
Hydration
Oxidation & Reduction
A substance is oxidised when
It gains oxygen
Or loses hydrogen
2Cu + O2 2CuO Copper (Cu) is oxidised
A substance is reduced when
It gains hydrogen
Or loses oxygen
CuO + H2 Cu + H2O Copper oxide (CuO) is reduced
Salts
Salts
•Are formed when a metal atom replaces the hydrogen atom(s) in an acid
•Are usually soluble
The acids that are needed to be known about are
•Sulphuric acid - H2SO4 - makes sulphates
•Hydrochloric acid - HCl - makes chlorides
•Nitric Acid - HNO3 - makes nitrates
Metal oxide + acid metal salt + water
Magnesium Oxide + sulphuric Acid magnesium sulphate + water
MgO + H2SO4 MgSO4 + H2O
Metal Hydroxide + acid metal salt + water
Sodium Hydroxide + Hydrochloric acid sodium chloride + water
NaOH + HCl NaCl + H2O
Metal carbonate + acid metal salt + water + carbon dioxide
Calcium carbonate + nitric acid calcium nitrate + water + carbon dioxide
CaCO3 + HNO3 Ca(NO3)2 + H2O + CO2
Neutralisation
When an acid is added to an alkali
Equal amounts of the acid and alkali react together
Technique for measuring amounts is called titration
Titration can be used to measure concentrations of alkaline solutions and acids
Preparation of oxygen
Decomposition of hydrogen peroxide in the presence of manganese dioxide catalyst
Hydrogen peroxide oxygen + water
H2O2 O2 + H2O
Preparation of hydrogen
React a metal with acid
Magnesium + Hydrochloric acid magnesium chloride + hydrogen
Mg + 2HCl MgCl2 + H2
Collection of gases
Upward displacement of water – suitable for a low density, insoluble gas e.g. oxygen or hydrogen
Downward displacement of air – suitable for a dense, soluble gas e.g. chlorine
Gas syringe – suitable for soluble gases, e.g. ammonia or carbon dioxide
Tests for common gases
Oxygen - relights a glowing spill
Hydrogen - “pop” test with a lit spill
Carbon dioxide - turns limewater cloudy (or milky)
Ammonia - forms a white smoke with hydrochloric acid vapour
Chlorine - bleaches moist indicator paper
Metal extraction
An ore is any rock containing commercially useful amounts of a metal
Metals often found as oxides or sulphides
The method used to extract a metal depends upon the reactivity of that metal
Unreactive metals (below hydrogen in the reactivity series) e.g. gold, platinum
Often found un-combined (or “native”) in the ore
Ore simply broken up and the pure metal extracted
Sometimes simple heating of the ore is required to extract the metal
Metals in the middle of the reactivity series (above hydrogen, below carbon)
Metal compound converted to oxide if not already
Heated with carbon, the metal is displaced by the carbon
Carried out in a blast furnace
Reactive metals (above carbon in the reactivity series)
Extraction is more difficult
Either displacement using a more reactive metal (Titanium Chloride + sodium titanium + sodium chloride)
Or use electrolysis (e.g. aluminium or sodium)
Carbonates
Decompose on heating (thermal decomposition) to give the oxide and carbon dioxide
Calcium carbonate Calcium Oxide + carbon dioxide
CaCO3 CaO + CO2
Hydrogen carbonates
Decompose readily on heating to give the oxide, carbon dioxide and water
Sodium hydrogen carbonate sodium oxide + carbon
dioxide + water
Hydration
When a substance has water present it is said to be hydrated, If the water is removed it is dehydrated or anhydrous
E.g. anhydrous copper sulphate is a pale blue/grey colour, addition of a small amount of water to the anhydrous salt turns it into the dark blue hydrated salt.
Anhydrous copper sulphate + water hydrated copper sulphate
CuSO4 + 5H2O CuSO4.5H2O Dehydration is the reverse, for example heating the hydrated copper sulphate will give the anhydrous form and water