Chemistry

• Reaction of Metals with Acids

  When acids react with metals, hydrogen and a salt are always formed. The first part of the salt's name comes from the metal involved. The second part of the name comes from the acid.
• Reaction of metals with acids

  • Magnesium + hydrochloric acid → magnesium chloride + hydrogen
  • Zinc + sulfuric acid → zinc sulfate + hydrogen
  • Iron + sulfuric acid → iron sulfate + hydrogen
• Redox reactions


  1. Reduction reaction (one reactant gains electrons)

  2. Oxidation reaction (one reactant loses electrons)
• Magnesium


  Magnesium atoms are oxidised (loses electrons) to become Mg2+ ions
• Chlorine


  Cl- ions are unchanged. They are spectator ions and aren't included in the ionic equation.
• Hydrogen


  H+ ions are reduced (gains electrons) to become hydrogen atoms. The atoms join together to form H2 gas.
• Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
• Neutralisation of Acids


  Acids can be neutralised by reacting with bases (an alkali is a base that dissolves in water)
• Examples of bases


  • Metal carbonates
  • Metal oxides
  • Metal hydroxides
• Acid + metal oxide


  Salt + water
• Acid + metal carbonate


  Salt + water + carbon dioxide
• Acid + metal hydroxide


  Salt + water
• Soluble salts


  Salts which dissolve in water
• Making soluble salts


  Reaction between acids and solid, insoluble substances such as pure metals, metal oxides, metal hydroxides, or metal carbonates
• Soluble salt


  • Blue copper sulfate
• Producing blue copper sulfate


  Add black copper oxide to sulfuric acid
• Cuos + H2SO4(aq) → CuSO4(aq) + H₂O
• Separating mixtures


  1. Gently warm the acid with a Bunsen burner

  2. Add the insoluble solid with stirring until the reaction no longer happens

  3. Filter the solution to remove the excess insoluble solid

  4. Heat the solution in an evaporating basin above a beaker of water

  5. Let the solution cool and allow more water to evaporate
• Mixture separation techniques


  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography
• pH scale


  • Measures the acidity or alkalinity of a solution, ranging from 0 to 14
  • pH 7 is neutral
  • pH less than 7 is acidic
  • pH more than 7 is alkaline
• Acids


  Form hydrogen (H+) ions when they dissolve in water
• Alkalis


  Form hydroxide (OH-) ions when they dissolve in water
• For every increase of 1 in pH, the concentration of H+ ions gets divided by 10
• Universal indicator


  The indicator changes to a particular colour depending on the pH of a solution
• pH probe


  The probe returns a number that represents the pH of a solution
• Titrations


  Measures the volumes of acid and alkali solutions needed in a neutralisation reaction
• Burette


  • Used in titrations
• Key variables in titrations

  • Acid
  • Alkali
  • Indicator
• If neutralising an alkali with an acid

  Titration can be used to calculate the concentration of the alkali if the concentration of the acid and volume of the alkali are known
• Indicators


  Show the end point of titrations by suddenly changing colour when the solution turns from acidic to alkaline, or alkaline to acidic
• Choosing an indicator


  • The strength of the acid and alkali must be considered
  • Suitable indicators for strong acid and alkali: Methyl orange (yellow in alkali, red in acid)
  • Phenolphthalein (pink in alkali, colourless in acid)
• Strong acids


  Fully ionise in water, meaning that all of the acid molecules break up to form H+ ions
• Weak acids


  Only partially ionise in water, meaning that not all of the acid molecules break up to form H+ ions
• Weak acids


  • Ethanoic acid (the main ingredient in vinegar)
• Most acids are weak acids
• Acid strength


  Determined by how much the acid ionises in water, not the concentration of the acid
• Acidic substances


  • Hydrochloric acid
  • Vinegar
  • Acid rain
• Neutral substances


  • Water
  • Blood
• Alkalis


  Substances that form hydroxide (OH-) ions when they dissolve in water (aqueous solutions)
• Acids


  Substances that form hydrogen (H+) ions when they dissolve in water (aqueous solutions)