CAIE IGCSE Chemstry笔记分享：Acids, bases and salts

IGCSEChemistry

今天为大家分享CAIE IGCSE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 (+ CO₂when 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 dm³of 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

Type of Salt Required	Acid used
Sulphate	Sulphuric acid
Nitrate	Nitric acid
Chloride	Hydrochloric acid
Ethanoate	Ethanoic acid

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