Chapter 9 Aqueous Solutions Predicting Solubilities

Solubility Chemists express solubility (S) as: mass of solute dissolved per 100 mL of water or moles of solute per litre of solution

Solubility Generally, it is agreed that: if solute has S > 0.1 mol/L, it is classified as SOLUBLE. if solute has S < 0.01 mol/L, it is classified as INSOLUBLE. if solute has S between 0.1 mol/L and 0.01 mol/L, it is classified as PARTLY or SLIGHTLY SOLUBLE. for our purposes, if S < 0.1 mol/L, it is classified as INSOLUBLE.

Solubility Rules …are determined experimentally. …can be used as a guideline to predict solubility. Use the solubility table on periodic table handout from class

Table 1: Solubility of Ionic Compounds at SATP ANION Cl-, Br-, I- S2- OH- SO42- CO32- PO43- SO32- C2H3O2- NO3- ClO3- C A T High Solubility > 0.1 mol/L (at SATP) most Group 1, NH4+, Group 2 Sr2+, Ba2+, Tl+ Group 1, NH4+ all I O N Low Solubility < 0.1 mol/L Ag+ Pb2+, Tl+, Hg22+ Cu+ Ag+ Pb2+ Ca2+ Ba2+ Sr2+ Ag+ none Ca2+

Solubility Rules- Others? See p334 Table 9.1 (5 rules, higher number takes priority) See p336 Language Link !

Solubility Examples Is the compound Soluble (S) or Insoluble (I)? PbCl2 KNO3 Li2CO3 Ans I S

Solubility Factors Many, but not all ionic compounds, are soluble in water. Why not all? There are several factors: 1. Ion Charge Compounds with higher ion charge tend to be insoluble because when the charge is inc., the force that holds ions together is inc. e.g PO43- has large ion charge and is insoluble

Solubility Factors 2. Ion Size - When atoms gain e-, ion size is larger e.g. Cl + e-  Cl- (non-metals) - When atoms lose e-, ion size is smaller e.g. Na  Na+ + e- (metals) larger smaller

Solubility Factors 2. Ion Size - continued Small ions bond more closely than large ions ∴cmpds with small ions are less soluble If you compare ions in the same family in the periodic table, as you go down the family, ion size inc ∴ solubility inc.

Homework Textbook Read p330-331, 334 Do p335 #1-3 p336 #1-6 (See answers on p367) BLM 9-1 and 9-4 (See answers on website)