CAIE IGCSE化学笔记分享：Acids, bases and salts

IGCSE Chemistry

今天为大家分享CAIE IGCSE化学酸碱盐（Acids, bases and salts)部分笔记总结。 

Properties of Acids 

• An acid is a compound which when dissolved in water produces hydrogen ions (H + ) and are described as proton donors (H + ) 
• Acids turn blue litmus indicator paper (or solution) red. 
• Have pH 1 to 6 
• Acid + metal → salt + hydrogen gas 
• Acid + base → salt + water 
• Acid + metal carbonate → salt + carbon dioxide + water 
• Strong acids completely ionize in water producing lots of H⁺ions 
• Weak acids partially ionize in water producing few H⁺ions

Properties of Bases 

• Bases are insoluble substances which neutralize acids to form a salt and water only and are proton acceptors 
• Alkalis turn red litmus indicator paper (or solution) to blue. 
• Have pH 8 to 14. 
• Base + acid → salt + water (+ CO₂ when base is a metal carbonate) 
• Base + ammonium salt → salt + ammonia gas + water 
• Strong alkalis completely ionize in water producing lots of OH^-ions 
• Weak alkalis partially ionize in water producing OH^-ions 

Neutral 

• Neutral substances are pH 7. 
• Acidity in soil: 

Plants grow at a pH near 7. 

• If it is too acidic or alkaline they will not grow. Acidic soil is fixed by adding lime.

• pH is the concentration of H⁺ions per dm³ of solution 

Indicators

Types of Oxides 

• Metal oxides are basic e.g. iron oxide and magnesium oxide 
• Non-metal oxides are acidic e.g. sulphur oxide and carbon dioxide 
• Aluminum, zinc and lead form amphoteric oxides e.g. zinc oxide 
• Oxides which are neither acidic or basic are neutral e.g. water and carbon monoxide

Preparation of Salts 

• A salt is a substance formed when all the replaceable hydrogen ions of an acid are replaced by metal ions or the ammonium ion 

• Salts can either be soluble or insoluble

Type of Salts

Starting with a Metal 

• Add excess metal to an acid 
• When bubbling (hydrogen) stops the reaction is done 
• Filter off excess metal 

Starting with an Insoluble Base 

• Add insoluble base to acid and heat gently, it will dissolve 
• Keep adding until no more dissolves (reaction is done) 
• Filter out the insoluble (excess) base

Starting with an Alkali (Titration) 

• Put a certain amount alkali in a flask 
• Add phenolphthalein 
• Add acid from a burette, stirring, until it goes colorless 
• Find out how much acid you used 
• Repeat, to be more accurate 
• Evaporate water from neutral solution 

Test for Aqueous Cations 

Test for Anions

Test for Gases