CHEMICAL CHANGES

• what is oxidation?

  Loss of electrons and gain of oxygen
• what is reduction?

  gain or electrons and the loss of oxygen
• oxidation and reduction always occur together
• metal reacts with oxygen to form what?

  Metal oxides
• what happens when magnesium is burned in air?

  it reacts with oxygen to form magnesium oxide and therefore gaining oxygen so it is oxidised
• what happens when lead is heated with carbon?

  the lead oxide loses oxygen so it is reduced, the carbon gains oxygen so is oxidised
• when metals react, their atoms lose electrons to form positive metal ions
• some metals lose electrons more easily then others
• the reaction of metals with acid and water cn be used to place them in order of reactivity~
• what happens when metals react with acids?

  they produce metal salts and hydrogen
• lithium, sodium and potassium are very reactive metals

  • they react vigorously with water to produce a metal hydroxide solution and hydrogen
  • they are placed at the top of the reactivity series
  • they would react so vigorously with dilute acids that it would not be safe to carry out these reactions
• calcium, magnesium, zinc and iron are fairly reactive metals

  they react quickly with acids and slowly with water
• copper and gold are very unreactive metals

  they do not react with water or acids and are placed at the bottom of the periodic table
• the reactivity series often includes carbon and hydrogen for comparison
• what is a displacement reaction?

  when a more reactive metal will displace a less reactive metal from a solution of its salt
• what is the reactivity series?

  1. potassium
  2. sodium
  3. calcium
  4. magnesium
  5. aluminium
  6. carbon
  7. zinc
  8. iron
  9. tin
  10. lead
  11. hydrogen
  12. copper
  13. silver
  14. gold
  15. platinum
• what does the method of extraction depend on?

  how reactive the metal is
• where do unreactive metals exist?

  as elements at the Earth's surface
• what are non metals found as?

  metal oxides, or compounds that can be easily changed into metal oxides
• how can metals less reactive then carbon be extracted?

  can be extracted from their oxides by heating with carbon
• iron oxide + carbon --> iron + carbon dioxide

  • the iron oxide loses oxygen so it is reduced
  • the carbon gains oxygen so it is oxidised
• not all reduction and oxidation reactions involve oxygen because of this scientists follow these rules:

  • oxidation is the loss of electrons
  • reduction is the gain of electrons
• what happens when a substance dissolves in water?

  they dissociate into their individual ions

  • hydroxide ions OH(-) make solutions alkaline
  • hydrogen ions H(+) make solutions acidic
• what is the pH scale a measure of?

  acidity or alkalinity of an aqueous solution

  • a solution with pH 7 is neutral
  • aqueous solutions with a pH less than 7 are acidic
  • the closer to a pH of 0 the stronger the acid
  • aqueous solutions with a pH of more than 7 are alkaline
  • the closer to a pH of 14 the stronger the alkali
• how can the pH of a solution be measured?

  pH probe , universal indicator
• what is an indicator?

  dyes that change colour depending on whether they are acidic or alkaline solutions:

  • litmus changes colour from red to blue or vice versa
  • universal indicator is a mixture of dyes that shows a range of colours to indicate how acidic or alkaline a substance is
• what is a soluble base called?

  alkalis
• how are acids neutralised?

  bases
• acid + metal hydroxide --> salt + water
• what do acids contain?

  hydrogen ions
• what do alkalis contain?

  hydroxide ions
• what happens when an acid reacts with an alkali?

  • the H(+) and OH(-) ions react together to produce water H2O which has a pH of 7 - this is called neutralisation
• why is it called neutralisation?

  • acid is neutralised by an alkali
  • the solution that remains has a pH of 7 showing it is neutral
• acid + metal oxide --> salt + water
• acid + metal carbonate --> salt + water + carbon dioxide
• what is produced when the hydrogen in the acid is replaced by a metal ion?

  Salt
• the name of salt depends on the acid used:

  • hydrochloric acid produces chloride salts
  • nitric acid produces nitrate salts
  • sulfuric acid produces sulfate salts
• how can soluble salts be made?

  by reacting acids with insoluble bases such as metal oxides, metal hydroxides and metal carbonates
• RP: Crystallisation - METHOD

  1. measure 40cm^3 of sulfuric acid
  2. gently warm the acid
  3. add excess of copper oxide
  4. stir with a glass rod
  5. filter the mixture using a filter funnel and filter paper, to remove excess unreacted copper oxide.
  6. pour copper sulphate solution into evaporating basin
  7. gently heat over a bunsen burner until half to all of the water has evaporated
  8. remove from heat and place in a cool dry place to allow to cool and crystalise, leave for 24 hours
• what are strong acids?

  are completely ionised (split up into ions) in water

  an example of a strong acid is hydrochloric/nitric/sulfuric