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Chemistry Slides Chemistry Slides Presentation Transcript

  • Acids, Bases and Salts 1
  • Acids Definition: Acids are chemical substances that produces hydrogen ions as the only positively charged ion when dissolved in water  Acids taste sour  pH < 7  Corrosive  Conducts electricity when aqueous  Turns blue litmus paper red 2
  • Acids: Strong or weak? Strong acid Weak acid   Ionizes completely in water Ionizes partially in water   Produces a lot of H+ ions Produces little H+ ions   All acid molecules form ions Not all acid molecules form ions   Very corrosive Not so corrosive   Mineral acids Organic acids   Strong electrolyte Weak electrolyte   3 View slide
  • Complete Ionisation in SA Cl- H+ Cl H Cl Cl - H H H+ Cl- Cl H Cl - Cl + H H+ – HCl  H + Cl + 4 View slide
  • Partial Ionisation of WA CH3COO H CH3COO H H CH3COO H CH3COO CH CH C OO 3 CO + H 3 O- H H H OO OO C C CH 3 CH 3 CH3COOH  H+ + CH3COO– 5
  • Strong Acids  Hydrochloric acid, HCl  Sulphuric acid (UK); Sulfuric acid (US), H2SO4  Nitric acid, HNO3 6
  • Weak Acids  Natural acids/Food acids  Ethanoic/Acetic acid (Found in vinegar)  Citric acid (Found in lime/lemon)  Malic acid (Found in apple) 7
  • Reactions of Acids with Reactive Metals  Acid + Metal  Salt + Hydrogen  Eg. Hydrochloric acid + Zinc   Zinc chloride + Hydrogen Not applicable to non-reactive metals like copper, silver and gold… 8
  • Reactions of Acids with Metal Carbonates  Acid + Metal Carbonate  Salt + Carbon Dioxide + Water  Eg. Hydrochloric Acid + Sodium carbonate  Sodium chloride + carbon dioxide + water 9
  • Bases Definition: A class of chemical substances which include all metal oxide, hydroxides, ammonium oxide and hydroxides  Calcium oxide – quicklime  Calcium hydroxide – limewater  Sodium hydroxide  Magnesium oxide etc… 10
  • Alkali Definition: An alkali is a soluble base that produces hydroxide ions as the only negatively charged ions when dissolved in water  Feel soapy to touch  Taste bitter  pH > 7  Corrosive  Conduct electricity when aqueous  Turn red litmus paper blue 11
  • Reaction of Alkali with Ammonium Salts  Alkali + Ammonium Salt  Salt + Ammonia + Water  Eg. Sodium hydroxide + Ammonium chloride  Sodium chloride + Ammonia + Water 12
  • Neutralization  Acid + Base  Salt + Water  Eg. Hydrochloric acid + Sodium hydroxide  Sodium chloride + Water Ionic equation for acid-alkali neutralization: H+ (aq) + OH– (aq)  H2O (l) 13
  • Salts Definition: A salt is the substance formed when the hydrogen of an acid is partially or totally replaced by a metal 14
  • Basicity  The number of hydrogen atoms in an acid that can be replaced by a metal is called Basicity  Eg. Hydrochloric acid with 1 hydrogen atom is monobasic  Sulphuric acid with 2 hydrogen atoms is dibasic  Phosphoric acid with 3 hydrogen atoms is tribasic 15
  • Acid Salts  Definition: Only part of the hydrogen present in the acid is replaced by a metal  Eg. Sodium hydrogensulphate  Sodium hydrogencarbonate, Baking soda 16
  • Uses  Salts are used in chemicals, soaps & detergents, photography, food & flavourings, medical uses, paints and fertilizers, etc…  Eg. Ammonium nitrate used as a fertilizer, Zinc sulphide in luminous paints, sodium fluoride in toothpaste, barium carbonate as a rat poison, calcium sulphate used as plaster 17
  • Indicators  Definition: Indicators are dyes, or mixtures of dyes, which changes colour when acids or alkalis are added to them 18
  • Indicators 19
  • Power of Hydrogen When pH decreases, the concentration of  hydrogen ions increases. When pH increases, the concentration of  hydrogen ions decreases. pH values lesser than 7, shows that it is acidic.  More hydrogen ions than hydroxide ions. pH values greater than 7 shows that it is  alkaline. More hydroxide ions than hydrogen ions. At pH 7, it is neutral. Hydrogen and hydroxide  ions are in equal concentration. 20
  • Types of Oxides  Basic oxides  Amphoteric oxides  Acidic oxides  Neutral oxides 21
  • Basic Oxides Oxides of metals  Mostly insoluble in water – refer to solubility  table Soluble basic oxides will dissolve in water to  form alkalis Sodium oxide dissolves readily in water to for sodium  hydroxide Reacts with acids and undergoes neutralization  reactions Eg. Copper(II) oxide, calcium oxide, magnesium  oxide Does not react with bases  22
  • Amphoteric Oxides Oxides of metals that react with both acids and  bases Eg. ZnO + 2HCl  ZnCl2 + H2  In the presence of acid, the amphoteric oxide  behaves like a base ZnO + 2NaOH  Na2ZnO2 + H2O  In the presence of alkali, the amphoteric oxide  behaves like an acid Others include aluminium oxide and lead(II)  oxide and lead(IV) oxide 23
  • Acidic Oxides  Oxides of non-metals  Soluble in water to produce acids  Eg. CO2 + H2O  H2CO3  Acidic oxides reacts with alkalis and undergoes neutralization reactions  Eg. Sulfur dioxide, sulfur trioxide, nitrogen dioxide, phosphorus(V) oxide  Does not react with acids 24
  • Neutral Oxides  Oxides of non-metals  Insoluble in water  Will not react with acids nor bases  Eg. Water, carbon monoxide, nitrogen monoxide 25
  • Water of crystallization 26
  • Hydrated salts  Salts that contain water of crystallization  Eg. Hydrated copper(II) sulphate  Chemical formula: CuSO4.5H2O  Crystalline solid held together by water molecules to form crystals  Salts without water of crystallization are called anhydrous salts  Water of crystallization can be removed by heating, water is driven off 27