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Acids & Bases


PROPERTIES OF ACIDS

  • Corrosive ('burns' your skin)
  • Sour taste (e.g. lemons, vinegar)
  • Contains hydrogen ions (H+) when dissolved in water
  • Has a pH less than 7
  • Turns blue litmus paper to a red colour
  • Reacts with bases to form salt and water
  • Reacts with metals to form hydrogen gas
  • Reacts with carbonates to form carbon dioxide, water and a salt

EXAMPLES OF ACIDS

  • Hydrochloric acid (HCl) in gastric juice
  • Sulphuric acid (H2SO4)
  • Nitric acid (HNO3)
  • Carbonic acid in softdrink (H2CO3)
  • Uric acid in urine
  • Ascorbic acid (Vitamin C) in fruit
  • Citric acid in oranges and lemons
  • Acetic acid in vinegar
  • Tannic acid (in tea and wine)
  • Tartaric acid (in grapes)

PROPERTIES OF BASES AND ALKALIS

  • Corrosive ('burns' your skin)
  • Soapy feel
  • Has a pH more than 7
  • Turns red litmus paper to a blue colour
  • Many alkalis (soluble bases) contain hydroxyl ions (OH-)
  • Reacts with acids to form salt and water

EXAMPLES OF BASES AND ALKALIS

  • Sodium hydroxide (NaOH) or caustic soda
  • Calcium hydroxide ( Ca(OH)2 ) or limewater
  • Ammonium hydroxide (NH4OH) or ammonia water
  • Magnesium hydroxide ( Mg(OH)2 ) or milk of magnesia
  • Many bleaches, soaps, toothpastes and cleaning agents

THE pH SCALE

Acids & Bases

Common Acids

pH

Common Bases

pH

Hydrochloric acid
Sulphuric acid
Stomach juice
Lemons
Vinegar
Apples
Oranges
Grapes
Sour milk
White bread
Fresh milk
0.1
0.3
1-3
2.3
2.9
3.1
3.5
4
4.4
5.5
6.5
Human saliva
Distilled water
Blood plasma
Eggs
Seawater
Borax
Milk of magnesia
Ammonia water
Limewater
Caustic soda
6-8
7
7.4
7.8
7.9
9.2
10.5
11.6
12.4
14

INDICATORS

An indicator, when added to an acid, a neutral substance or a base, will change different colours.

INDICATOR COLOUR IN ACID COLOUR IN NEUTRAL SOLUTION COLOUR IN BASE
Litmus red purple blue
Bromothymol Blue yellow blue blue
Phenolphthalein clear clear purple
Universal Indicator red Yellow-green purple

REACTIONS WITH ACIDS

ACID + BASE Acids & Bases SALT + WATER
Hydrochloric Acid + Sodium Hydroxide Acids & Bases Sodium Chloride + Water
HCl + NaOH Acids & Bases NaCl + H2O

ACID + METAL Acids & Bases SALT + HYDROGEN GAS
Hydrochloric Acid + Magnesium Acids & Bases Magnesium Chloride + Hydrogen
HCl + Mg Acids & Bases MgCl2 + H2

ACID + CARBONATE Acids & Bases SALT + WATER + CARBON DIOXIDE GAS
Hydrochloric Acid + Calcium Carbonate Acids & Bases Calcium Chloride + Water + Carbon Dioxide
HCl + CaCO3 Acids & Bases CaCl2 + H2O + CO2