Unit 10: Reactivity of Metals - Comprehensive Notes

Reactivity of Metals

Introduction

• This unit explores the reactivity of various metals with oxygen, water, and dilute acids.
• We will use word equations to describe these reactions.
• Some substances are inert, meaning they are generally unreactive.

Key Questions

• Reactants: Substances that participate in a chemical reaction.
• During a reaction, the amount of reactants decreases.
• Products: New substances formed in a chemical reaction.
• Evidence of a chemical reaction includes observable changes when substances are combined.

Reactivity of Specific Metals

Sodium (Na)

• Highly reactive, requiring storage under oil to prevent reaction with air or moisture.
• Soft and easily cut with a knife.
• Tarnishes in air due to reaction with oxygen.

Iron (Fe)

• Reacts with air and water to form iron oxide (rust).
• $4Fe + 3O<em>2 + 6H</em>2O \rightarrow 4Fe(OH)_3$
• The rusting process is slow and occurs over an extended period.

Understanding Reactivity

• Reactivity measures how readily a substance undergoes a chemical reaction.
• Different metals exhibit different levels of reactivity.

Reactions with Oxygen

• Most metals react with oxygen to produce a metal oxide.
• Examples when heating metals:
  • Copper: Forms a black powder coating (Copper Oxide).
    • $2Cu(s) + O_2(g) \rightarrow 2CuO(s)$
  • Iron: Glows and produces yellow sparks, leaving behind a black powder (Iron Oxide).
    • $4Fe(s) + 3O<em>2(g) \rightarrow 2 Fe</em>2O_3(s)$
  • Sodium: Bursts into yellow flames, forming a white powder (Sodium Oxide).
    • $4Na(s) + O<em>2(g) \rightarrow 2Na</em>2O(s)$
  • Gold: Remains unchanged, indicating its low reactivity.

Reactions with Water

• Calcium: Sinks, produces hydrogen bubbles on the surface, and forms Calcium Hydroxide, making the water cloudy.
  • $Ca(s) + 2H<em>2O(l) \rightarrow Ca(OH)</em>2(aq) + H_2(g)$
  • Hydrogen gas can be tested using a glowing splint, which will cause a 'pop' sound.
• Copper: Sinks and does not react with water.
• Sodium: Floats, fizzes, produces gas, and bursts into flames, creating a clear solution of Sodium Hydroxide.
  • $2Na(s) + 2H<em>2O(l) \rightarrow 2NaOH(aq) + H</em>2(g)$
• Iron: Sinks and does not react with water.
• Magnesium: Sinks and reacts very slowly with water to produce Hydrogen.
  • $Mg(s) + 2H<em>2O(l) \rightarrow Mg(OH)</em>2(aq) + H_2(g)$
• Potassium: Floats and bursts into flames immediately.
  • $2K(s) + 2H<em>2O(l) \rightarrow 2KOH(aq) + H</em>2(g)$

Reactions with Acid

• Metals react with acid to produce a metal salt and hydrogen gas.
• Lead:
  • Does not react with dilute acid.
  • Reacts slowly with concentrated acid, producing hydrogen bubbles.
• Zinc: Reacts slowly with dilute acid, producing hydrogen bubbles slowly.
  • $Zn(s) + 2HCl(aq) \rightarrow ZnCl<em>2(aq) + H</em>2(g)$
• Copper: Does not react with dilute or concentrated acid.
• Magnesium: Reacts very quickly with acid, producing Hydrogen.
  • $Mg(s) + 2HCl(aq) \rightarrow MgCl<em>2(aq) + H</em>2(g)$

Reactivity Series

• A list of metals arranged in order of their reactivity, based on tests with oxygen, water, and acids.
• Metals are arranged in descending order of reactivity.
• Inert substances are unreactive and placed at the bottom of the series.

Summary of Reactions

• Reactants are on the left side of the arrow, and products are on the right side in a word equation.
• Metal + Oxygen → Metal Oxide
• Metal + Water → Metal Hydroxide + Hydrogen
• Some Metals + Hydrochloric Acid → Metal Chloride + Hydrogen
• The reactivity series organizes metals from most to least reactive.
• Inert substances are generally unreactive.

Review Questions

1. Why is sodium kept under oil? To prevent it from reacting with moisture and oxygen in the air.
2. What happens to copper when heated in oxygen? It forms a black powder (Copper Oxide).
3. What happens to gold when heated in oxygen? It remains unchanged due to its low reactivity.
4. If a metal reacts with oxygen, what is the product? Metal Oxide.
5. If a metal reacts with water, what is the product? Metal Hydroxide and Hydrogen.
6. Name two metals that float on water. Sodium and Potassium.
7. What is phenolphthalein and what is it used for when testing metals and water? Phenolphthalein is an indicator used to test for alkalinity; it turns pink in the presence of a base, such as metal hydroxides formed when reactive metals react with water.
8. What is the purpose of the reactivity series and what tests are used to set it up? The reactivity series organizes metals by their reactivity, determined through reactions with oxygen, water, and acids.
9. What is rust and how does it form? Rust is Iron Oxide, formed when iron reacts with air and water.