Solubility of Compounds with Different Polarities

5.4 Introduction

Y12 Chem

​What we will cover

• ​describe and analyse the processes involved in the dissolution of ionic compounds in water

• ​solubility and solubility rules

• ​solubility product

• ​Ksp calculations

​Dissolution of Ionic Compounds

• ​separating of positive and negative ions from a solid ionic compound, forming hydrated ions when dissolved in water = dissociation

  • ​ionic bonds in lattice are broken

  • ​hydrogen bonds in water are broken

  • ​ion-dipole attractions form between ions and polar water molecules

​Solubility

• ​soluble or insoluble

  • ​the energy required to separate the ions from the lattice is greater than the energy released when the ions are hydrated

• ​maximum amount of solute that can be dissolved in a given quantity of a solvent

​Solubility Rules

• ​Revision from Year 11

• ​Reality is that ionic substances that are classified as insoluble, can still dissolve to some extent

• ​Solubility depends on the difference in the energy required to separate the ions from the lattice, and the energy released when the ions are hydrated

Multiple Choice

Considering the following precipitation reaction:

Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)

What is the correct complete ionic equation?

• Pb²⁺ + (NO₃)₂^- + 2K⁺ + 2I^- → PbI₂(s) + 2K⁺ + 2NO₃^-

• Pb²⁺ + 2NO₃^- +2K⁺ + I^- → PbI₂(s) + 2K⁺ + NO₃^-

• Pb²⁺ + 2NO₃^- + 2K⁺ + 2I^- → PbI₂(s) + 2K⁺ + 2NO₃^-

• Pb²⁺ + 2NO^3- + 2K⁺ + 2I^- → Pb²⁺ + 2I^- + 2K⁺ + 2NO₃^-

Multiple Choice

Which of the following is insoluble in water?

• Ammonium Hydroxide

• Barium Hydroxide

• Potassium Hydroxide

• Zinc Hydroxide

​Saturated Solutions

• ​contains the maximum amount of solute that can be dissolved at a particular temperature

• ​we should call bsolids, sparingly soluble

  • ​e.g. NaCl solutions are