Displacement Reactions and Reactivity Series Study Guide

Lesson Overview and Academic Context

• School: Al Nahda National School for Boys.
• Vision Statement: Everyone engages, everyone reflects, everyone learns.
• Grade Level: 8BP.
• Subject: Chemistry.
• Term/Week: Term 3, Week 25 (Distance/Synchronous Learning).
• Value of the Week: Global Understanding.
• Theme/Quote: "Strong values, bright dreams, and a proud heritage — this is the future of our children."

Competencies and National Identity

• Core Competencies:
  • Communication
  • Innovation
  • Social Responsibility
  • Collaboration
  • Digital Citizenship
  • Problem Solving
  • Creativity
  • Global Awareness
  • Adaptability
  • Critical Thinking
  • Cultural Awareness
  • Flexibility
• National Identity Domains:
  • Domain 1 (Culture): Includes Elements of Arabic Language, History, and Heritage.
  • Domain 2 (Values): Includes Elements of Respect, Compassion, and Global Understanding.
  • Domain 3 (Citizenship): Includes Elements of Belonging, Volunteering, and Conservation.

Lesson Objectives and Success Criteria

• Learning Objective (9Cc.02): Identify examples of displacement reactions and predict products. This is limited to reactions involving calcium ($Ca$), magnesium ($Mg$), zinc ($Zn$), iron ($Fe$), copper ($Cu$), gold ($Au$), and silver ($Ag$) salts.
• Success Criteria:
  • Identify displacement reactions by recognizing when a more reactive metal replaces a less reactive metal from its compound.
  • Predict the products of displacement reactions using the reactivity series.

Fundamental Principles of Displacement Reactions

• Basic Definition: A displacement reaction is a chemical process where a more reactive element displaces (removes and replaces) a less reactive element from its compound.
• Primary Rule:
  • A reaction happens when the single metal is more reactive than the metal currently in the compound.
  • A reaction does not happen when the single metal is less reactive than the metal in the compound form.

The Reactivity (Activity) Series of Metals

The reactivity series lists metals from the most reactive to the least reactive. This order is essential for predicting the outcome of reactions.

1. Potassium ($K$): Most Reactive (can displace all metallic ions in a compound).
2. Sodium ($Na$)
3. Calcium ($Ca$)
4. Magnesium ($Mg$)
5. Aluminum ($Al$)
6. Zinc ($Zn$)
7. Iron ($Fe$)
8. Lead ($Pb$)
9. Hydrogen ($H$)
10. Copper ($Cu$)
11. Mercury ($Hg$)
12. Silver ($Ag$)
13. Gold ($Au$)
14. Platinum ($Pt$): Least Reactive (cannot displace any metallic ion in a compound).

Chemical Equations and Examples

General Displacement Reactions

• Calcium + Copper Sulfate:
  • $Ca + CuSO_4 → CaSO_4 + Cu$
  • Result: Calcium Sulfate + Copper
• Magnesium + Silver Nitrate:
  • $Mg + 2AgNO_3 → Mg(NO_3)_2 + 2Ag$
  • Result: Magnesium Nitrate + Silver
• Zinc + Iron(II) Sulfate:
  • $Zn + FeSO_4 → ZnSO_4 + Fe$
  • Result: Zinc Sulfate + Iron
• Iron + Copper Chloride:
  • $Fe + CuCl_2 → FeCl_2 + Cu$
  • Result: Iron(II) Chloride + Copper
• Copper + Silver Nitrate:
  • $Cu + 2AgNO_3 → Cu(NO_3)_2 + 2Ag$
  • Result: Copper(II) Nitrate + Silver
• Gold + Copper Sulfate:
  • $Au + CuSO_4 → \text{No Reaction}$
  • Reason: Gold is less reactive than Copper.

Displacement from Metal Oxides

• Iron + Copper(II) Oxide:
  • $2Fe + 3CuO → Fe_2O_3 + 3Cu$
  • Result: Iron(III) Oxide + Copper
• Aluminum + Zinc Oxide:
  • $2Al + 3ZnO → Al_2O_3 + 3Zn$
  • Result: Aluminum Oxide + Zinc

Measurable Characteristics and Observations

When a displacement reaction occurs, several physical changes can be observed:

• Color Change:
  • Example: The blue color of an aqueous Zinc-Copper sulfate solution ($Cu^{2+}$) decreases.
  • Example: In a reaction between an iron nail and copper sulfate, the solution turns light green because iron ($Fe^{2+}$) ions enter the solution while displacing copper.
• Solid Formation: A new solid metal appears, either coating the surface of the original metal or settling at the bottom.
• Mass Changes:
  • In the case of an iron nail in copper sulfate solution, the mass of the actual iron in the nail decreases because iron atoms leave the solid state to become ions in the liquid solution.
• Temperature Change: The reactions are typically exothermic, giving off heat and making the container feel warm.

Non-Metal Displacement (Group 7 Halogens)

Displacement also occurs among non-metals, particularly halogens in Group 7.

• Reactivity Trend: Reactivity increases up the group ($F > Cl > Br > I > At$).
• Molecular Logic:
  • The outer electron is closer to the nucleus as you move up the group.
  • This results in higher attraction, making it easier for the atom to gain an electron.
• Reactivity Trend for Group 1 (Alkali Metals): Reactivity increases down the group because the outer electron is further from the nucleus, resulting in lower attraction and making the electron easier to lose.
• Halogen Reaction Examples:
  • $Br_2(aq) + 2KI(aq) → 2KBr(aq) + I_2(aq)$ (Probable reaction: Bromine displaces Iodine).
  • $Br_2(aq) + KCl(aq) → \text{No Reaction}$ (Bromine is less reactive than Chlorine).
  • $I_2(s) + KBr(aq) → \text{No Reaction}$ (Iodine is less reactive than Bromine).

Practice Exercises

Predictive Logic

• Iron + Copper oxide: Possible (Iron is more reactive than Copper).
• Copper + Iron oxide: Not possible.
• Lead + Magnesium oxide: Not possible (Magnesium is much higher in the reactivity series than Lead).
• Aluminum + Zinc oxide: Possible (Aluminum is more reactive than Zinc).

Completion Exercises

1. Zinc + Silver sulfate: Yields Zinc sulfate + Silver.
2. Copper + Zinc nitrate: No reaction (Copper is less reactive than Zinc).
3. Magnesium + Calcium chloride: No reaction (Magnesium is less reactive than Calcium).
4. Magnesium + Iron chloride: Yields Magnesium chloride + Iron.

Questions & Discussion

Question: What can you infer about the reaction between iron and copper sulfate? Answer: Iron is more reactive than copper, leading to a displacement reaction.

Question: Why can iron react with copper sulfate? Answer: Because iron sits higher in the reactivity series compared to copper.

Question: Why does the solution change color during the iron/copper sulfate reaction? Answer: The solution turns light green because $Fe^{2+}$ ions, which are naturally pale green, enter the solution as they displace the blue copper ions.

Question: Would the mass of the iron nail be greater or less than its starting mass? Why? Answer: The mass would be less because iron atoms are leaving the solid nail to become aqueous ions.

Question: Which metal can displace all metallic ions in a compound? Answer: Potassium ($K$).

Question: Which metal cannot displace any metallic ion in a compound? Answer: Platinum ($Pt$).