Metals

Metals

1. REACTIONS

   • Acid+Metal
     • Produce hydrogen gas and salt
     • Ionic Equation : M + H+ = Mx+ + H2
     • More shells, weaker attractive forces, easier to lose valence electrons
     • Potassium,sodium : dangerously explosive Calcium : reacts vigorously Magnesium : less vigorously Zinc : moderately fast Iron,lead : react slowly Copper,silver,gold : no reaction
   • Metal+Cold Water
     • Produce metal hydroxide and hydrogen gas
     • Iron does not react with cold water!
     • Why different reactions? : Group I reacts more vigorously than Group II as it is more reactive. Increasingly difficult to lose one electron at a time, increasingly difficult to lose 2nd electron from a positively charged ion.
     • Potassium : reacts vigorously, produces lilac flame Sodium : reacts vigorously, produces orange flame Calcium : reacts rapidly (denser than Grp 1 metals) Magnesium : react slowly Zinc,iron,lead,copper,silver,gold : no reaction
   • Metal+Steam
     • Produce metal oxide + hydrogen
     • Why must metal be heated? : Provide energy to activate the reaction hence overcoming Ea.
     • Purpose of soaked glass wool? To produce steam
     • Why do boiling tube containing metal often crack? Reaction is highly exothermic . Sudden temperature difference of the tube causes it to crack
     • Potassium,sodium,calcium : react explosively. Reaction should not be carried out in the lab. Magnesium : heated magnesium reacts vigorously with steam Zinc : heated zinc reacts less vigorous than magnesium Iron : heated iron reacts slowly than steam Copper,silver,gold : no reaction with steam or water
     • Magnesium + Steam : Glows brightly with a white flame. White solid formed. Orange/Yellow light observed due to combustion of H2.
     • Zinc + Steam : Glows red hot with white flame. A yellow solid is formed. Yellow solid turns white when cool.
     • Iron + Steam : Grey/black iron powder glows red-hot. A red/orange/black solid is formed.
   • Displacement of Metals + Thermite Reactions
     • less reactive metal exists as ion more reactive metal exists as atom
     • More reactive metal displaces a less reactive metal from its compund
     • Generic observations : Solid deposited and colour change
     • Example : Fe (grey) + CuSO4 (blue) -> Cu (reddish-brown) + FeSO4 (green) Fe + Cu2+ -> Cu + Fe2+
     • Answering technique : Metal X is more reactive than Metal Y. Metal X displaces metal Y from the compound of Metal Y
     • The greater the difference in reactivity between two metals, the more heat released.
   • Thermal Stability of Metal Carbonate
     • Metal carbonate -> Metal Oxide + CO2 Reaction is endothermic
     • Measure volume of gas, fixed time. Measure time, fix volume of gas. Fix time, measure mass of solid. Measure time for precipitate to form in limewater. Measure mass loss in fixed time intervals. Constant variables : No of moles of carbonate, Surface area of carbonate, Flame intensity Independent variable : Type of carbonate Dependant variable : Volume of CO2,mass loss,time taken
     • As reactivity of metal increases,the more thermally stable is its carbonate.
     • Potassium,sodium : do not decompose Calcium,magnesium,aluminium,zinc,iron,lead,copper: decompose
   • Reduction of Oxides using hydrogen
     • Produce metal + carbon dioxide
     • Carbon & hydrogen is the RA.
     • 2CuO + C -> 2Cu+CO2
     • The more reactive the metal, the higher the temp needed for reduction
     • PbO + H2 -> Pb + H2O
     • Why hydrogen be dry? Ensure water is produced during reaction and not from wet hydrogen
     • Why supply of hydrogen onl stops after end of reaction? Prevent air from reacting with hot copper