Acids and Bases

Acids and bases neutralise each other:

• An acid is a substance that forms an aqueous solution with a pH of less than 7 and they form H+ ions in water.
• A base is a substance that will react with an acid to form a salt.
• An alkali is a base that disolves in water to form a solution with a pH greater than 7 and they form OH- ions in water.

The reaction between acids and bases is called neutralisation:

acid + base ----> salt + water

H+ (aq) + OH- (aq) ----> H20 (L)

> Hydrogen ions react with hydroxide ions to produce water

Metal oxides and metal hydroxides are bases:

• Some metal oxides and metal hydroxides dissolve in water. These soluble compounds are alkalis.
• Even bases that won't dissolve in water still take part in neutralisation reactions with acids.
• So all metal oxides and metal hydroxides react with acids to form a salt and water:

Acid + Metal Oxide/Metal Hydroxide ----> Salt + Water

The comination of metal and acid decides the salt:

• Hydrochloric acid + copper oxide = copper chloride + water
• Hydrochloric acid + sodium hydroxide = sodium chloride + water
• Sufuric acid + zinc oxide = zinc sulfate + water
• Sulfuric acid + calcium hydroxide = calcium sulfate + water
• Nitric acid + magnesium oxide = magnesium nitrate + water 
• Nitric acid + potassium hydroxide = potassium nitrate + water

Acids and metal carbonates produce carbon dioxide:

• Metal carbonates are also bases. They will react with acids to produce a salt, water and carbon dioxide:

Acid + Metal Carbonate ----> Salt + Water + Carbon Dioxide

The reactivity series (most reactive to least reactive):

• Potassium (K)
• Sodium (Na)
• Lithium (Li)
• Calcium (Ca)
• Magnesium (Mg)
• Carbon (C)
• Zinc (Zn)
• Iron (Fe)
• Hydrogen (H)
• Copper (Cu)

Some metals react with acids to produce a salt and hydrogen gas:

Acid + Metal ----> Salt + Hydrogen

How metals react with acids tells you about their reactivity:

• The speed of reaction is indicated by the rate at which the bubbles of hydrogen are given off.
• The more reactive the metal, the faster the reaction will go. Very reactive metals ike potassium, sodium, lithium and calcium react explosively, but less reactive metals such as magnesium, zinc and iron react less violently. In general, copper won't react with cold, dilute acids.
• You can use the burning splint test to confirm that hydrogen is formed in these reactions.

Formation of metal ore: Oxidation = Gain of Oxygen

Extraction of metal: Reduction = Loss of Oxygen

OILRIG= OXIDATION IS LOSS, REDUCTION IS GAIN

Metal displacement reactions are redox reactions:

A MORE REACTIVE metal will displace a LESS REACTIVE METAL

EXAMPLE:

If you put iron in a solution of copper sulfate, the more reactive iron will kick out the less reactive copper from the solution, so you end up with the iron sulfate solution and the copper metal:

iron + copper sulfate = iron sulfate + copper

In this reaction the iron loses 2 electrons to become a 2+ ion so it's oxidised. 

The copper ion gains these 2 electrons to become a copper atom so it's reduced.

• In metal displacement reactions, it's always the metal ION that gains electrons and is reduced.
• The metal ATOM always loses electrons and is oxidised.