Metal Reactivity and the Reactivity Series Study Notes

Introduction to Metal Reactivity

• Metals possess varying tendencies to undergo chemical reactions. Some metals react explosively, others react moderately, and some do not react at all.

• The reactivity of a metal refers to its tendency to undergo a chemical reaction.

• To identify if a chemical reaction has taken place, several observations can be made, including:

  • The emmision of light.

  • A change in temperature (heat).

  • A change in color.

The Reactivity Series

• The reactivity series (or activity series) is a definitive list that arranges metals in order of their reactivity, with the most reactive metals at the top and the least reactive metals at the bottom.

• This list is constructed using results from various chemical investigations, such as reactions with oxygen, water/steam, and dilute acids.

• The Reactivity Series (from Most to Least Reactive):

  • Potassium ($K$): Most reactive metal.

  • Sodium ($Na$).

  • Barium ($Ba$).

  • Calcium ($Ca$).

  • Magnesium ($Mg$).

  • Aluminium ($Al$).

  • Carbon ($C$): Often included as a reference element.

  • Zinc ($Zn$).

  • Iron ($Fe$).

  • Nickel ($Ni$).

  • Tin ($Sn$).

  • Lead ($Pb$).

  • Hydrogen ($H$): Included as a critical reference point; metals above hydrogen can displace it from acids, while those below cannot.

  • Copper ($Cu$).

  • Mercury ($Hg$).

  • Silver ($Ag$).

  • Gold ($Au$).

  • Platinum ($Pt$): Least reactive metal.

Mnemonic for Remembering the Reactivity Series

• Students can use the following mnemonic to remember the order of metals:

  • Please: Potassium ($K$)

  • Stop: Sodium ($Na$)

  • Calling: Calcium ($Ca$)

  • Me: Magnesium ($Mg$)

  • A: Aluminium ($Al$)

  • Careless: (Carbon)

  • Zebra: Zinc ($Zn$)

  • Instead: Iron ($Fe$)

  • Try: Tin ($Sn$)

  • Learning: Lead ($Pb$)

  • How: (Hydrogen)

  • Copper: Copper ($Cu$)

  • Saves: Silver ($Ag$)

  • Gold: Gold ($Au$)

Reaction of Metals with Dilute Acids

• The position of a metal relative to Hydrogen ($H$) in the reactivity series determines if it will react with dilute acid.

• Metals above Hydrogen in the series will react with dilute acids to produce a salt and hydrogen gas (evidenced by fizzing or effervescence).

• Metals below Hydrogen do not react with dilute acids.

• Specific Observations with Dilute Acids:

  • Potassium ($K$): Far above Hydrogen; reaction is violently explosive.

  • Sodium ($Na$): Far above Hydrogen; reaction is very violent.

  • Calcium ($Ca$): Above Hydrogen; reaction is very vigorous.

  • Magnesium ($Mg$): Shows very vigorous effervescence.

  • Zinc ($Zn$): Shows steady/fast effervescence.

  • Iron ($Fe$): Shows slow effervescence of gas.

  • Copper ($Cu$): Below Hydrogen; NO REACTION. No fizzing and no change in the solution or metal.

  • Silver ($Ag$): Below Hydrogen; NO REACTION. No fizzing and no change.

Reaction of Metals with Oxygen (Oxidation)

• Group 1 Metals (Alkali Metals):

  • These metals tarnish almost instantly when exposed to the air. This is due to the formation of a layer of metal oxide (which can progress to peroxides or superoxides).

  • Storage Requirement: Because of their extreme reactivity with air, Group 1 metals must be stored under oil to prevent exposure to oxygen and moisture.

  • Example Chemical Equation: $4Na(s) + O_2(g) \rightarrow 2Na_2O(s)$

• Effect of Heating:

  • Potassium, Sodium, and Calcium: Burn brightly when heated in air to form an oxide.

  • Magnesium, Zinc, and Iron: Show a slow reaction when heated to form an oxide.

  • Silver and Gold: Show no reaction even when heated.

• The Exception of Iron:

  • Iron undergoes a unique form of oxidation called rusting. Unlike other metal oxides that may form a protective layer, iron oxide (rust) is flaky and non-protective. This allows the process of corrosion to continue until the metal is entirely consumed.

Reaction of Metals with Water and Steam

• Group 1 Metals: All Group 1 metals react vigorously with cold water.

  • Products: They produce a metal hydroxide (which is an alkali) and hydrogen gas.

  • General Equation: $2M(s) + 2H_2O(l) \rightarrow 2MOH(aq) + H_2(g)$

  • Specific examples: Potassium and Sodium react very vigorously in cold water.

• Transition Metals:

  • Most transition metals do not react with cold water.

  • Iron Exception: Iron does not react with cold water but will react with steam (hot water vapor).

  • Chemical Equation for Iron and Steam: $3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)$

• Summary of Reactivity with Water:

  • Potassium, Sodium: Very vigorous reaction in cold water; hydroxide forms.

  • Calcium: Slow reaction in cold water; hydroxide forms.

  • Magnesium, Zinc, Iron: Reactivity decreases down the list; reaction only occurs with steam.

  • Copper, Silver, Gold: No reaction with steam or water.

Displacement Reactions

• Definition: A displacement reaction occurs when a more reactive metal takes the place of a less reactive metal within a chemical compound.

• The Iron and Copper Sulfate Case Study:

  • If a clean iron nail is placed in a beaker containing blue copper sulfate solution, the following occurs:

    1. The blue color of the copper sulfate solution changes to a slightly paler color.

    2. The nail undergoes a color change, becoming coated in a reddish-brown layer of copper.

  • The Science: Iron is more reactive than copper. Therefore, the iron displaces the copper from the sulfate solution to form iron sulfate.

  • Word Equation: $\text{Copper sulfate} + \text{iron} \rightarrow \text{iron sulfate} + \text{copper}$

  • Symbol Equation: $CuSO_4 + Fe \rightarrow FeSO_4 + Cu$

• Summary Rules for Displacement:

  • More reactive metals displace less reactive metals.

  • Less reactive metals cannot displace more reactive metals from their compounds.

  • Example of non-reaction: $\text{copper} + \text{zinc sulfate} \rightarrow \text{No reaction}$ (Because copper is lower in the reactivity series than zinc).

Practice Assessment and Guidelines

• Question 1: Reactivity Investigation

  • Scenario: A student adds copper, iron, magnesium, and zinc to dilute hydrochloric acid.

  • Observations (Describe):

    • Copper: No reaction and no effervescence.

    • Iron: Slow effervescence of gas.

    • Zinc: Steady or fast effervescence.

    • Magnesium: Very vigorous effervescence.

  • Reactivity Order (Least to Most): Cu < Fe < Zn < Mg

• Question 2: Zinc and Copper Sulfate Reaction

  • Reaction: $Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)$

  • Type of Reaction: Displacement reaction (also classified as a redox reaction).

  • Explanation: The reaction occurs because zinc is more reactive than copper.

  • Solution Color Change: The solution changes from a blue solution to a colorless solution as copper sulfate is consumed and zinc sulfate is formed.

  • Ionic Equation: $Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)$

• Common Mistakes to Avoid:

  • Avoid including spectator ions in ionic equations.

  • Ensure all charges are correctly balanced in the chemical equations.

Keywords and Definitions

• Reactivity: The tendency of a substance to undergo a chemical reaction.

• Reactivity Series: A list of metals arranged in order of their reactivity from the most reactive to the least reactive.

• Displacement Reaction: A reaction where a more reactive element takes the place of a less reactive element in a compound.