Unit 13: Metals and reactivity

Unit 13: Metals and reactivity

1. Describe the general physical and chemical properties of metals

   • Metals are good conductors of electricity and heat, malleable, ductile, shiny.
   • Most metals have high melting and boiling points, high densities, react with acids to give off hydrogen gas, form positive ions when they react.

2. Explain why metals are used in the form of alloys

   • Alloys are mixtures of metal atoms with other metal atoms or non-metal atoms. Metals are made into alloys to improve their strength, hardness or resistance to corrosion.

3. Identify alloys from diagrams of their structure

4. Describe the order of reactivity K, Na, Ca, Mg, Zn, Fe and Cu

   • Order of the metal reactivity series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au

5. Describe the relative reactivity of K, Na, Ca, Mg, Zn, Fe and Cu with water or steam

   • Only metals above hydrogen in the reactivity series will react with water or steam.
     • Na: reacts violently with cold water ~ Ca: reacts rapidly with cold water ~ Mg: reacts very slowly with cold water but reacts rapidly with steam ~ Zn: only reacts when powdered and heated strongly in steam ~ Cu: no reaction with cold water or steam

6. Describe the relative reactivity of K, Na, Ca, Mg, Zn, Fe and Cu with dilute HCl (aq)

   • Only metals above hydrogen in the reactivity series react with hydrochloric acid.
     • Na: very violent - explosive ~ Ca: very rapid - lots of hydrogen bubbles produced ~ Mg: rapid - bubbles of hydrogen produced steadily ~ Zn: slow - bubbles of hydrogen produced slowly ~ Cu: no reaction with dilute or concentrated acid

7. Deduce an order of reactivity from experimental results

   • See previous points.
   • Metals can be arranged in a reactivity series by comparing how easily they react with water, steam and hyrdochloric acid.

8. Explain metal reactivity in terms of ease of formation of metal ions

   • A more reactive metal loses its valency electrons more easily than a less reactive metal. The ease with which a metal loses its valency electrons to form ions depends on the distance of the valency electrons from the nucleus, the nuclear charge and the number of electron shells.

9. Describe the reactivity series by reference to the reaction of metals with metal ions

   • A more reactive metal displaces a less reactive metal from a solution of its salt. Each atom of the more reactive metal loses electrons and each ion of the less reactive metal gains electrons.

10. Describe the reactivity series in terms of the reaction of metal oxides with carbon

    • Metal oxides below carbon in the reactivity series are reduced to their metals when heated with carbon. Metals more reactive than carbon have to be extracted using electrolysis.

11. Explain why aluminium is apparently unreactive

    • Aluminium is high in the reactivity series but doesn't seem to react with water or acids. It will only react with acids when it is freshly made. This is because, when the surface of freshly made aluminium is left in the air, a thin layer of aluminium oxide quickly forms on its surface. This thin layer is enough to make the metal resistant to corrosion. The tough metal oxide layer sticks to the surface of the aluminium very strongly and doesn't flake off. The oxide layer is unreactive.

12. Describe the action of heat on metal hydroxides and nitrates

    • Metal hydroxides
      • Most metal hydroxides decompose to form a metal oxide and water when heated.
    • Nitrates
      • The alkali metal nitrates decompose to form a nitrite and oxygen when heated, e.g. potassium nitrate --heat--> potassium nitrite + oxygen.
      • Nitrates of other metals decompose to form an oxide, nitrogen dioxide and oxygen when heated, e.g. magnesium nitrate --heat--> magnesium oxide + nitrogen dioxide + oxygen
      • Nitrates of very unreactive metals decompose to form the metal, nitrogen dioxide and oxygen when heated, e.g. silver nitrate --heat--> silver + nitrogen dioxide + oxygen

13. Link the thermal decomposition of hydroxides and nitrates to the reactivity series

    • Thermal decomposition = the breakdown of a compound into two or more substances by heat
    • The more reactive the metal, the more stable its nitrate, hydroxide or carbonate (the harder it gets to decompose them).

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