Salts (ss1 revision)

Salts

  • Definition: A salt is a compound formed when all or part of the replaceable hydrogen ion of an acid is replaced by a metallic or ammonium ion.

Types of Salts

  • Normal Salts: Formed when all replaceable hydrogen ions in the acid are completely replaced by metallic ions.

    • Example: HCl(aq) + NaOH(aq) ➔ NaCl(aq) + H2O(l)

  • Acidic Salts: Formed when only some hydrogen ions are replaced by a metal.

    • Example: H2SO4(aq) + KOH(aq) ➔ KHSO4(aq) + H2O(l)

  • Basic Salts: Occur when there is not enough acid for complete neutralization of the base.

    • Example: Ca(OH)2 + HCl ➔ Ca(OH)(Cl) + H2O (not complete neutralization)

  • Double Salts: Salts composed of two different metallic ions and one anion. General formula: (SO4)x(M+)(M3+).

    • Example: KAl(SO4)2 • 12H2O or (NH4)2Fe(SO4)2 • 6H2O

  • Complex Salts: Contain complex ions with a charged group of atoms.

    • Example: K4[Fe(CN)6] or Sodium Tetrahydroxozincate.

Uses of Salts

  • Ammonium Chloride: Used as an electrolyte in dry cells.

  • Calcium Carbonate (CaCO3): Used to neutralize acidity in the stomach.

  • Calcium Chloride: Used as antifreeze.

  • Potassium Nitrate (KNO3): Used for making gunpowder and as a fertilizer.

  • Calcium Sulfate: Used for making plaster of Paris.

Recovering Soluble Salts

  • Methods:

    1. Heating to dryness

    2. Crystallization

    3. Preparation from insoluble salts through double decomposition.

Hydrolysis

  • Definition: The reaction of a salt with water, producing either an acidic or alkaline solution.

    • Example: Na2CO3 + H2CO3 ➔ 2NaOH + CO2 (producing basic solutions).

Drying Agents

  • Definition: Substances used to absorb moisture in laboratory settings.

Types of Drying Agents

  • Hygroscopic Agents: Absorb moisture from the environment.

  • Deliquescent Agents: Absorb so much moisture they form a solution.

Common Drying Agents

  • Concentrated H2SO4: Effective for most gases except ammonia and hydrogen sulfide.

  • Fused Calcium Chloride: All gases except ammonia.

  • Calcium Oxide: Particularly suitable for ammonia.

  • Silica Gel: Suitable for all gases.

Non-Ionic Reactions and Equations

  • Compounds such as acids, alkalis, and salts that dissolve in water tend to dissociate into ions. Interaction between these ions can lead to reactions.

Example Reaction

  • HCl(aq) + NaOH(aq) ➔ NaCl(aq) + H2O(l)

Crystallization Calculation Example

Question:When a sample of a salt is heated, water is lost. If the mass of the salt before heating is 5.0g and the mass of the water lost is 1.80g, calculate the mass of the anhydrous salt remaining after heating.

Steps to Solve:

  1. Identify the information provided:

    • Mass of salt before heating = 5.0g

    • Mass of water lost = 1.80g

  2. Set up the calculation:

    • Since the mass of the anhydrous salt is found by subtracting the mass of the water lost from the original mass of the salt, the equation will be:

    Mass of anhydrous salt = Mass of salt before heating - Mass of water lost

  3. Perform the calculation:

    • Mass of anhydrous salt = 5.0g - 1.80g = 3.20g

  4. Conclusion:

    • The mass of the anhydrous salt remaining after heating is 3.20g.