Chemistry, 8: Acids, bases, and salts

• An aqueous solution is formed when a substance dissolves in water

  It can be acidic, alkaline, or neutral
• A neutral solution is neither acidic or alkaline
• Red litmus papers show acidic solutions
• Blue litmus paper shows alkaline solution
• Phenolphthalein indicator is colourless in acid, but pink in alkaline solutions
• Methyl orange is pink in acid, but yellow in alkaline solution.
• Acids are substances that contains replaceable hydrogen atoms

  They can be replaced by metal atoms to form salts
• Acids have a pH of 0-6
• What are some common acids?

  Hydrochloric acid, HCl

  Nitric acid, HNO3

  Sulfuric acid, H2SO4

  Phosphorous acid, H3PO4
• Acidic properties are only seen when water is present

  In water, acids form hydrogen ions

  H+ ions create this acidic properties
• Acids are proton donors

  E.g.

  HCl -> H+ + Cl-
• What happens when an acid and metal reacts?

  Makes salt and hydrogen gas
• What happens when an acid and carbonate reacts?

  Makes salt, carbon dioxide, and water
• What happens when an acid and base reacts?


  Makes salt and water
• Bases are oxides and hydroxides of metals
• Alkalis form when oxides or hydroxides of a metal dissolves in water

  E.g. sodium + oxygen -> sodium oxide

  sodium oxide + water -> sodium hydroxide
• Sodium oxide is a base because it is the oxide of sodium

  It reacts with water to make alkali sodium hydroxide
• What happens when a base and acid reacts?

  Forms salt and water
• What happens when a base and ammonium compound reacts?

  Forms ammonia gas
• Alkalis only show alkaline properties in presence of water

  In water, alkalis form OH- ions

  These OH- ions reacts with H+ ions from acid to make water
• Alkalis are proton acceptors
• If soil is too acidic, it can be neutralised with quicklime
• Quicklime is made from limestone

  It is heated in lime kilns at 1200°C to make calcium oxide

  When it is added to water, it makes calcium hydroxide, an alkali that neutralizes the soil
• Oxides of elements are made by heating it in air or oxygen
• Basic oxides that dissolves in water are alkalis
• Oxides that do not dissolve in water can be identified using pH

  Or tested to react with:

  HCl, a basic oxide

  NaOH, acidic oxide

  If they do not react with either they are neutral oxides
• Most metals are basic oxides

  Basic oxides react with acids

  Acid + base -> salt + water
• Most non-metal oxides are acidic

  Acidic oxides react with bases (neutralisee) and dissolves in water to form acid
• Metal oxides react with acids to make salt + water
• Non-metal oxides react with base to make salt + water
• Amphoteric oxides are oxides of less reactive metals

  They behave as both acid and basic oxides
• Neutral oxides do not react with acids or bases
• Acids contain replaceable hydrogen atoms which is replaced by metal to form a salt
• What are common acids and salts?

  HCl, Cl-

  HNO3, NO3-

  H2SO4, SO4^2-

  H3PO4, PO4^3-
• Salts are ionic compounds which are found in the form of crystals
• Salts that don’t contain water are anhydrous
• All common sodium, potassium, and ammonium salts are soluble
• All nitrates are soluble
• Common chlorides, bromides, and iodides are soluble

  Excluding silver chloride, silver bromide, and silver iodide
• Common sulfates are soluble

  Except barium, lead, and calcium