Reactivity of Metals

Unit 10: The Reactivity of Metals

Learning Objectives

• At the end of the lesson, students must be able to:

  • Identify and explain the reactivity series.

  • Explain how the reactivity series is constructed.

  • Describe the reactions of metals with oxygen, water, and dilute acids.

  • Identify the more reactive metal out of a pair.

  • Know how to use word equations to describe reactions.

  • Explain the term inert.

Reactivity of Metals with Oxygen

• Metals can react with oxygen when heated, producing metal oxides. This reaction can be represented by the general word equation:

  • Metal + Oxygen → Metal Oxide

Observations from Reactions with Oxygen

• Copper:

  • Does not burn; develops a black coat.

• Iron (Iron Wool):

  • Glows and produces yellow sparks; black powder forms after reaction (iron oxide).

• Sodium:

  • Bursts into yellow flames; forms a white substance (sodium oxide).

• Gold:

  • No reaction occurs.

Reactivity of Metals with Water

• Water, a compound of hydrogen and oxygen, can react with metals to form metal hydroxides and hydrogen gas, represented by:

  • Metal + Water → Metal Hydroxide + Hydrogen

Testing for Products

• Phenolphthalein Indicator: Changes from colorless to pink when metal hydroxide is produced.

• Hydrogen Gas Test: A lit splint tests for hydrogen gas. A popping sound indicates its presence.

Observations from Reactions with Water

• Calcium:

  • Sinks, bubbles of hydrogen form slowly then quickly increase; water becomes cloudy as calcium hydroxide forms.

• Copper:

  • Sinks and does not react.

• Sodium:

  • Floats on the surface, bubbles form quickly around it, bursts into flames; produces a clear solution of sodium hydroxide.

• Iron:

  • Sinks and does not react.

• Magnesium:

  • Sinks, bubbles of gas form very slowly, yields magnesium hydroxide.

• Potassium:

  • Floats, bursts into flames immediately with rapid bubbling; produces clear potassium hydroxide solution.

Reactivity of Metals with Dilute Acids

• Some metals react with dilute acids to produce metal salts and hydrogen gas, represented by:

  • Metal + Acid → Metal Salt + Hydrogen

Safety Note

• Metals like potassium and sodium react violently with acids; such reactions should not be conducted in a classroom or experimental setting.

Observations from Reactions with Dilute Acids

• Lead:

  • No reaction with dilute acids, reacts slowly with concentrated acids.

• Zinc:

  • Reacts slowly with dilute acids.

• Copper:

  • No reaction.

• Magnesium:

  • Reacts quickly with dilute acids.

Experimental Setup for Metal Reaction with Dilute Acid

• To compare metal reactivity, measure the amount of hydrogen gas produced:

  • Place a piece of metal in a test tube or conical flask.

  • Pour acid into the flask using a thistle funnel.

  • Observe for hydrogen gas bubbles. Collect gas after a minute to allow it to push out the air.

  • The collected hydrogen gas will displace water in the upturned test tube.

Example Reaction

• Calcium with Hydrochloric Acid:

  • Reaction: Calcium + Hydrochloric Acid → Calcium Chloride + Hydrogen

  • Products: calcium chloride (metal salt) and hydrogen (gas).

  • Hydrogen test: A lighted splint tests for hydrogen gas; a popping sound confirms its presence.

The Reactivity Series

• The reactivity series is constructed based on the reactions observed between metals and oxygen, water, and dilute acids.

• Metals are arranged in order of reactivity, with the most reactive metals at the top.

• Inert Substances: These are materials that do not react with other substances, indicating their lack of reactivity.

Summary of the Reactivity of Metals