Acids Bases and Salts

==Acid and Base/Alkali Reactions==

  • Acid + Metal → salt + hydrogen
    • Sulphuric acid + iron→ iron sulphate + hydrogen
  • Base/alkali + acid → salt + water
    • Sodium hydroxide + hydrochloric acid  Sodium chloride + water
  • Acid + metal carbonate → salt + carbon dioxide + water
    • Nitric acid + magnesium oxide  magnesium nitrate + carbon dioxide + water
  • Alkali + ammonium salt → salt + ammonia + water
    • Sodium hydroxide + ammonium chloride  sodium chloride + ammonia + water

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  • ==Acid: Proton Donors/ Dissociate into H+ ions==

    • Have pH between 1 (strong) and 6 (weak)
    • Turns blue litmus red
    • Turns methyl orange indicator red

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  • ==Bases: Proton Acceptors/ Dissociate into OH- ions==

    • Are the oxides and hydroxides of metals
    • Neutralise acids to give a salt and water only
    • Are mainly insoluble in water
  • Alkalis: (are bases that dissolve in water)

    • Feel soapy to the skin
    • Turn litmus blue
    • Gives solutions with a ph greater than 7
    • · Give solutions that contain OH – ions

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==Neutrality, acidity, alkalinity==

  • pH scale runs from 1 – 14

Key facts:

  • Acids have a ph less than 7
  • The more acidic a solution, the lower the ph
    • Neutral substances, such as pure water have a ph of 7
    • Alkalis have ph greater than 7
    • Strong acid or base completely ionize in water
    • Weak acids partially ionize in water Ways to Measure pH:

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  • Substances that change colour when added to an acid/alkali are called indicators. They are often in solution form but can also be found as paper

==Metal and non-metal oxides==

  • Acidic oxides: Non-metal oxides that dissolve in water and form an acidic solution
  • Basic oxides: Metal oxides that dissolve in water and form basic solution
  • Neutral oxides: Oxides with a pH of 7. Do not react with Acids or Alkalis
    • However there some exceptions for this rule, for example carbon monoxide.
  • Amphoteric oxides: those that react with both an acid and an alkali to give a salt and water.

eg. zinc and aluminum oxides

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Preparing Salts

==Preparing Soluble Salts==

Method A: Neutralization

  • Excess insoluble compound (metal/base/carbonate) reacts with acid whilst being heated
  • Insoluble base is filtered out
  • Solution is heated in an evaporating dish to form soluble salt crystals

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Method B: Titration

  • Phenolphthalein is added to an alkali (soluble base)
  • Add acid to solution using burette; note volume of acid required for solution to change color
  • Repeat without indictor using noted acid volume
  • Heat in evaporating dish to form soluble salt crystals

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==Preparing Insoluble Salts==

Method C: Precipitation

  • 2 soluble salts added to water and mixed

    Note: one soluble salt should always be a potassium or sodium solution (eg. potassium sulfate)

  • Filter out and clean precipitate with distilled water

  • Dry insoluble salt precipitate in oven

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Tests

==Testing Cations==

CationAqueous NaOHAqueous Ammonia
Aluminum (Al3+)White soluble precipitate, turns colorless in excessWhite precipitate, insoluble in excess
Ammonium (NH4+)Pungent ammonium gas produced turns damp red litmus blue
Calcium (Ca2+)White precipitate, insoluble in excessFaint or no precipitate
Copper (Cu2+)^^Blue precipitate, insoluble in excess^^^^Blue precipitate, soluble in excess to give a dark blue solution^^
Iron(II) (Fe2+)%%green precipitate, insoluble in excess%%%%green precipitate, soluble in excess%%
Iron(III) (Fe3+)==Reddish-brown precipitate, insoluble in excess====Reddish-brown precipitate, insoluble in excess==
Zinc (Zn2+)White precipitate, soluble and turns colorless in excessWhite precipitate, soluble and turns colorless in excess
Chromium (Cr3+)Grey green precipitate, soluble to give dark green solution in excessGrey green precipitate, insoluble in excess

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==Testing for Anions:==

  • Sulfate ions (SO42-):

    • Add dilute nitric acid, then add aq. barium nitrate
    • White precipitate formed
  • Sulphite ions (SO32-):

    • Add acidified potassium permanganate and heat
    • Color changes from pink to colorless

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  • Halide ions:
    • Add nitric acid, then aqueous silver nitrate
Chloride (Cl-)White precipitate
Bromide (Br-)Cream precipitate
Iodide (I-)Yellow precipitate

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  • Nitrate ions (NO3-):

    • Add aqueous sodium hydroxide then add warm aluminum foil
    • Pungent gas produced, turns damp red litmus blue
  • Carbonate ions (CO32-):

    • Add dilute hydrochloric acid
    • If bubbles/ gas produced turn limewater cloudy, carbonate ion present

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==Flame Tests==

==Test for Gases:==

GasTest result
Ammonia (NH3)Damp red litmus paper turns blue
Carbon dioxide (CO2)Bubble gas through–from colorless to cloudy
Chlorine (Cl2)Bleaches red/blue litmus paper
Hydrogen (H2)Place lighted splint, squeaky pop
Oxygen (O2)Place glowing splint, splint relights

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