Chemistry Slides

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Chemistry Slides

  1. 1. Acids, Bases and Salts 1
  2. 2. 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
  3. 3. 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
  4. 4. Complete Ionisation in SA Cl- H+ Cl H Cl Cl - H H H+ Cl- Cl H Cl - Cl + H H+ – HCl  H + Cl + 4
  5. 5. 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
  6. 6. Strong Acids  Hydrochloric acid, HCl  Sulphuric acid (UK); Sulfuric acid (US), H2SO4  Nitric acid, HNO3 6
  7. 7. Weak Acids  Natural acids/Food acids  Ethanoic/Acetic acid (Found in vinegar)  Citric acid (Found in lime/lemon)  Malic acid (Found in apple) 7
  8. 8. 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
  9. 9. Reactions of Acids with Metal Carbonates  Acid + Metal Carbonate  Salt + Carbon Dioxide + Water  Eg. Hydrochloric Acid + Sodium carbonate  Sodium chloride + carbon dioxide + water 9
  10. 10. 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
  11. 11. 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
  12. 12. Reaction of Alkali with Ammonium Salts  Alkali + Ammonium Salt  Salt + Ammonia + Water  Eg. Sodium hydroxide + Ammonium chloride  Sodium chloride + Ammonia + Water 12
  13. 13. 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
  14. 14. Salts Definition: A salt is the substance formed when the hydrogen of an acid is partially or totally replaced by a metal 14
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. Indicators  Definition: Indicators are dyes, or mixtures of dyes, which changes colour when acids or alkalis are added to them 18
  19. 19. Indicators 19
  20. 20. 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
  21. 21. Types of Oxides  Basic oxides  Amphoteric oxides  Acidic oxides  Neutral oxides 21
  22. 22. 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
  23. 23. 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
  24. 24. 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
  25. 25. Neutral Oxides  Oxides of non-metals  Insoluble in water  Will not react with acids nor bases  Eg. Water, carbon monoxide, nitrogen monoxide 25
  26. 26. Water of crystallization 26
  27. 27. 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

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