Reactivity in Chemistry

Reactions of metals

• Metals react with oxygen to form metal oxides

  • Metal + Oxygen → Metal Oxide

  • Example reactions:

    • Magnesium + Oxygen

    • Copper + Oxygen

• Metals react with water to produce hydrogen gas

  • Metal + Water → Metal Hydroxide + Hydrogen

  • Example reactions:

    • Sodium + Water

    • Potassium + Water

• Metals react with acids to produce hydrogen gas and a salt

  • Metal + Acid → Salt + Hydrogen

  • Example reaction:

    • Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen

Reactivity Series

• Different metals have different reactivities with chemical reagents

• Metals react by losing electrons to form positive ions

• More reactive metals readily lose electrons, while less reactive metals do so less readily

• More reactive metals displace less reactive metals from salt solutions

• Reactivity series from most reactive to least reactive:

  • Potassium (K)

  • Sodium (Na)

  • Calcium (Ca)

  • Magnesium (Mg)

  • Zinc (Zn)

  • Iron (Fe)

  • Lead (Pb)

  • Hydrogen (H)

  • Copper (Cu)

  • Silver (Ag)

Determining Reactivity

• Reactivity is determined through experimental observations in the laboratory

• Observations include reactions of metals with cold water, steam, and dilute acid

Reaction of Potassium with cold water

• Violent reaction

• Aqueous Potassium hydroxide is formed

• Hydrogen gas is liberated

• Potassium + Water → Potassium hydroxide + Hydrogen gas

• Hydrogen gas can burn in air

• Red litmus turns blue

Test for hydrogen gas

• Hydrogen gas can be tested by using a lighted splint, which goes off with a 'pop' sound

Reaction of Magnesium with cold water

• Reaction is very slow

• A few bubbles of hydrogen gas are produced

• Magnesium + Water → Magnesium hydroxide + Hydrogen gas

Reaction of Zinc with cold water

• No reaction occurs

• Zinc + Water → No reaction

Reaction of Metals with Steam

• Metals like Zinc and Iron do not react with cold water but react with steam

• Magnesium reacts violently with steam but reacts slowly with cold water

• Hydrogen gas is liberated

• Metal oxide is formed

Reaction of Magnesium with Steam

• Violent reaction

• Magnesium oxide (white powder) and hydrogen gas are produced

• Magnesium + Steam → Magnesium oxide + Hydrogen gas

• Hydrogen gas can burn in air

Reaction of Metals with Dilute Acid

• Many metals react with dilute acids to produce salt and hydrogen gas

• Metal + Dilute acid → Salt + Hydrogen gas

• When dilute hydrochloric acid is used, the products are metal chloride (salt) and hydrogen gas

Summary table of metal reactivity

• Reactive metals react with water or dilute acids

• Potassium and sodium have explosive reactions with water

• Calcium and magnesium have violent reactions with water

• Zinc reacts with steam

• Iron has a slow reaction with water

• Lead, copper, and silver do not react with water or steam

• Reactive metals tend to react with non-metals to form compounds

• Unreactive metals have a greater tendency to remain uncombined

Displacement Reactions

• An element higher in the reactivity series will displace an element lower than it from a compound

• More reactive element takes the place of the less reactive element

• Example: Adding magnesium to copper sulphate solution displaces copper, forming magnesium sulphate and copper

Complete the blanks

• Metal that reacts with hydrogen: Aluminium

• Hydrogen cannot remove oxygen from the oxide and oxide: Carbon

• Copper oxide + Copper + Water: Copper

• Can reduce zinc oxide into zinc: Carbon

• Lead + Lead oxide: No reaction

Possible reactions

• Iron + lithium sulfate → Iron sulfate + Lithium: Possible

• Zinc + copper sulfate → Zinc sulfate + Copper: Possible

• Magnesium + copper nitrate → Magnesium nitrate + Copper: Possible

• Potassium + tin chloride → Potassium chloride + Tin: Possible

• Silver + aluminium sulfate → Silver sulfate + Aluminium: Not possible

• Calcium + lead nitrate → Calcium nit