Acids and Bases

An Introduction

Acids

• A group of chemical compounds (more than one element) with similar properties

• Solutions of acids have a sour taste• Can be classified as strong or weak

– Sulfuric acid (H2SO4) is a strong acid used in car batteries– Hydrochloric acid (HCl) is a strong acid used to clean

mortar from bricks– HCl also used for digestion in stomach in weaker

solution

Common Acids and some everyday uses

Problems with acids

• Can cause contamination in waterways and threaten fish

• Acid rain causes soils to become ‘sour’ and stunts plant growth

• Steel and marble buildings are corroding faster than ever, due to increased levels of acidity of atmosphere

Bases

• Chemical compounds that are the opposite of acids• Bases that are soluble in water are called alkalis• Have a bitter taste and a soapy feel• Commonly used in the home as cleaning agents– Sodium hydroxide (NaOH- caustic soda) is a strong base

used to make soaps, drain cleaner and oven cleaner• A concentrated solution is corrosive (will burn the skin) and

poisonous

Common household bases and some everyday uses

Reactions of acids and bases

• When acids are added to bases, they cancel each other out– Called a neutralisation reaction

Example: – Indigestion, it is due to too much acid in the stomach;

Magnesium hydroxide, Mg(OH)2 is used to counteract the stomach acids

– Bee stings contain acid and can be treated with a base, such as ammonia

– Wasp stings contain a base, so they are better treated with an acid such as vinegar

Reactions of acids and bases

• In any neutralisation reaction, the acid and base combine to produce a salt and water

acid + base → salt + water

Eg. When hydrochloric acid reacts with sodium hydroxide, sodium chloride and water are formed.

Hydrochloric acid + sodium hydroxide → sodium chloride + water(acid) (base) (salt) (water)