Explaining Reactivity | Chemistry for Grade 11 (IGCSE) PDF Download

Explaining Reactivity

• When metals react with other substances, they form positive ions due to electron loss
• The reactivity of a metal is determined by its propensity to lose electrons
• A metal positioned higher in the reactivity series easily sheds electrons, showcasing higher reactivity compared to metals lower in the series

Displacement Reactions

• In displacement reactions between metals and aqueous solutions of metal salts, a more reactive metal displaces a less reactive metal from its salt solution
• For instance, when iron (Fe) is placed in a copper sulfate (CuSO4) solution, the iron displaces copper and forms iron sulfate (FeSO4) while copper is deposited
• This demonstrates the reactivity series in action, with more reactive metals displacing less reactive metals in solutions
• Any metal can displace another metal positioned lower in the reactivity series from a solution of one of its salts. This displacement phenomenon occurs because more reactive metals have a higher tendency to lose electrons and form ions compared to less reactive metals. Consequently, more reactive metals serve as better reducing agents.
• This reactivity trend is attributed to the fact that the less reactive metal acts as a superior electron acceptor when compared to the more reactive metal. Hence, the less reactive metal undergoes reduction in this process. Remember, according to the mnemonic OIL-RIG, reduction involves the gain of electrons.

Example

• Let's consider an example involving magnesium and copper sulfate. Magnesium, being a reactive metal, can displace copper from a copper sulfate solution.
• Magnesium exhibits a higher tendency to lose its electrons, leading to the ion of the less reactive metal, copper, accepting these electrons to form elemental copper. This reaction is visually evident as the more reactive metal gradually vanishes from the solution, displacing the less reactive metal.
• Magnesium displaces copper from a copper sulfate solution due to its higher reactivity.
• Magnesium's electron loss facilitates the transformation of copper ions into elemental copper.
• The displacement of copper by magnesium becomes apparent as the more reactive metal disappears, replacing the less reactive metal in the solution.
• The chemical reaction demonstrating the displacement of copper by magnesium in a copper sulfate solution results in the formation of magnesium sulfate and elemental copper. This can be symbolically represented as:
  Mg (s) + CuSO₄ (aq) → MgSO₄ (aq) + Cu (s)
• The blue color of the copper sulfate (CuSO₄) solution fades as colorless magnesium sulfate solution is formed.
• Copper coats the surface of the magnesium and forms a solid metal that falls to the bottom of the beaker.
• Diagram showing the color change when magnesium displaces copper from copper sulfate:
  
• By combining different metals and metal salts solutions, it is possible to determine a relative reactivity order.
  
• From the displacement table, we can deduce the order of reactivity:
• Magnesium and zinc are more reactive than iron, with magnesium being more reactive than zinc.
• Copper and silver are less reactive than iron, with silver being less reactive than copper.
• The order of reactivity of the metals tested: Mg > Zn > Fe > Cu > Ag.