Chemistry Chemical Changes

What is the general reaction between metals and oxygen?​

• Metal + Oxygen → Metal Oxide​

• This is an oxidation reaction where the metal gains oxygen.

How is the reactivity of a metal determined in reactions with acids?

• More reactive metals react more vigorously with acids.​

• They produce hydrogen gas and form salts more rapidly.​

What is the reactivity series of metals?

A list of metals ranked by their reactivity.

From Most to Least Reactive:

• Potassium (K)

• Sodium (Na)

• Lithium (Li)

• Calcium (Ca)

• Magnesium (Mg)

• Aluminum (Al)

• Carbon (C) – Used in metal extraction (reduces less reactive metal oxides).

• Zinc (Zn)

• Iron (Fe)

• Tin (Sn)

• Lead (Pb)

• Hydrogen (H) – Included to compare metal reactivity (metals below it don’t react with acids).

• Copper (Cu)

• Silver (Ag)

• Gold (Au)

• Platinum (Pt)

How can the reactivity series be determined using displacement reactions?​

• A more reactive metal will displace a less reactive metal from its compound.​

• For example, magnesium can displace copper from copper sulfate solution.

How are metals extracted based on their position in the reactivity series?

Metals more reactive than carbon (e.g., potassium, sodium) are extracted by electrolysis.

Metals less reactive than carbon (e.g., iron) are extracted by reduction with carbon.

What is a redox reaction?

A reaction where both reduction (gain of electrons) and oxidation (loss of electrons) occur simultaneously.

What is the general reaction between acids and metals?

Acid + Metal → Salt + Hydrogen​

How do acids react with metal oxides?

Acid + Metal Oxide → Salt + Water

What is the reaction between acids and metal carbonates?

Acid + Metal Carbonate → Salt + Water + Carbon Dioxide

How can soluble salts be prepared from acids and insoluble bases?

• Add excess base to the acid.

• Filter to remove unreacted base.

• Evaporate water to crystallize the salt.

What distinguishes strong acids from weak acids?

• Strong acids completely ionize in water (e.g., hydrochloric acid).

• Weak acids partially ionize in water (e.g., ethanoic acid).

How does pH relate to hydrogen ion concentration?

A decrease of one pH unit represents a tenfold increase in hydrogen ion concentration.

What is the difference between acid strength and acid concentration?

• Strength refers to the degree of ionization in water.

• Concentration refers to the amount of acid dissolved in a solution.

What is electrolysis?

The process of using electricity to decompose an electrolyte into its elements.

What happens to ions during electrolysis?

• Positive ions (cations) move to the cathode (negative electrode) and gain electrons (reduction).

• Negative ions (anions) move to the anode (positive electrode) and lose electrons (oxidation).

Why must the electrolyte be molten or in solution for electrolysis?​

To allow ions to move freely and conduct electricity.

How is aluminum extracted from its ore using electrolysis?

• Aluminum oxide is dissolved in molten cryolite to lower its melting point.

• Electric current is passed through, reducing aluminum ions to aluminum metal at the cathode.

What are the rules for determining products at the electrodes during electrolysis of aqueous solutions?

• At the Cathode (Negative Electrode):

  • If the metal is more reactive than hydrogen, hydrogen gas is produced.

  • If the metal is less reactive than hydrogen, the metal is deposited.

• At the Anode (Positive Electrode):

  • If halide ions (Cl⁻, Br⁻, I⁻) are present, the halogen gas is produced.

  • If no halide ions are present, oxygen gas is produced from hydroxide ions (OH⁻).

What are the products of electrolyzing aluminium oxide (Al₂O₃)?

• At the cathode (negative electrode): Aluminum ions (Al³⁺) are reduced to form aluminum metal:

  • Al³⁺(l) + 3e⁻ → Al(l)

• At the anode (positive electrode): Oxygen ions (O²⁻) are oxidized to form oxygen gas:

  • 2O²⁻(l) → O₂(g) + 4e⁻

What are the half-equations involving H⁺ and OH⁻ ions during electrolysis?

• At the Cathode (Negative Electrode):

  • H⁺ ions from the solution gain electrons to form hydrogen gas (H₂).

  • Half-equation:

    • 2H⁺(aq) + 2e⁻ → H₂(g)

• At the Anode (Positive Electrode):

  • OH⁻ ions from the solution lose electrons to form oxygen gas (O₂).

  • Half-equation:

    • 4OH⁻(aq) → O₂(g) + 2H₂O(l) + 4e⁻