14.3 Using reactivity series

Question 1

reactivity of a metal

Answer 1

• metals tend to lose electrons to form positive ions
• a more reactive metal has a greater tendency to form positive ions compared to a less reactive metal
• e.g. when K (potassium) reacts with H2O, it loses electrons to form positive ions
• Mg (magnesium) loses electrons less readily compared to K, does not react as violently to H2O

Question 2

Displacement reactions of metals

Answer 2

-more reactive metal displaces a less reactive one from its salt sol

Question 3

Displacement reactions of metals (e.g. copper and iron)

Answer 3

• iron more reactive, displaces copper
• e.g. iron fillings added to sol of blue copper (II) sulfate
• copper metal is precipitated out of sol as pink/reddish-brown solid
• sol turns green

Question 4

Are metal displacement reactions redox reactions?

Answer 4

• oxidation: lose electrons
• reduction: gain electrons
• in metal displacement reaction, more reactive metal is oxidised, less reactive one is reduced (redox reaction)
• e.g. occurs when magnesium displaces copper from copper(II) salt sol
• more reactive metal (Mg) displaces reduces copper(II) ions to copper
• Mg itself is oxidised to Mg ions

Question 5

Reaction between a metal and oxide with another metal

Answer 5

• a more reactive metal can reduce the oxide of a less reactive metal e.g. zinc and copper(II) oxide
• zinc more reactive than copper, form positive ions (Zn2+_ more readily
• Zn 2+ ions react with O2- ions from copper (II) oxide to form zinc oxide
• in the process, copper (II) oxide is reduced to copper
• Zn (s) + CuO (s) —> ZnO (s) + Cu (s)
• more reactive metals become ions more readily and form compounds

Question 6

Reduction of metal oxides with carbon

Answer 6

General eqn: metal oxide + carbon - (heat) –> metal and carbon dioxide

• e.g. 2CUO (s) [copper(II) oxide] + C (s) —> 2CU (g) +CO2 (g)
• the more reactive a metal is, the more difficult it is to reduce its oxide to metal by carbon
• oxides of metal can be reduced to their metals by heating it with carbon
• reaction is particularly impt in the extraction of some metals from ore
• apparatus: ceramic dish, wire gauze tripod stand

Question 7

Reduction of metal oxides with hydrogen

Answer 7

• oxides of some metals can be reduced to their metals by heating with hydrogen
• general eqn: metal oxide + hydrogen —> metal + steam
• e.g. PbO (s) [lead(II) oxide] + H2 (g) —> Pb(s) + H2O (g)
• more reactive metal, harder to reduce its oxide to metal by hydrogen
• oxides of reactive metals like PSCMZ not reduced by hydrogen

Question 8

Action of heat on metal carbonates

Answer 8

• only some carbonates can be decomposed by heat
• more reactive the metal, more difficult to decompose its carbonate by heat
• sodium and potassium (very reactive) are both heat stable, no reaction to prolonged heating
• thermal stability can be tested by heating them in a dry test tube

Question 9

Deducing the order of reactivity of metals

Answer 9

-more reactive metal displace the less reactive metal from the salt