Predicting Solubility of Ionic Compounds in Water: Guidelines and Examples

Using Tables F & G

Table F problems • Solubility guidelines for ionic substances in water • solubility ranges from very low solubility (basically insoluble) to very soluble • Use table F guidelines to predict if a given compound is soluble or insoluble

To use Table F • Separate the ionic compound into the positive ion and the negative ion • Scan for both in Table F • Left side of Table F shows soluble compounds with exceptions • Right side of Table F shows insoluble compounds with exceptions

Soluble – cmpd with a Group 1 ion Soluble – cmpd with NH4+ Soluble – cmpd with HCO3- Insoluble – sulfates with Ba+ Soluble – cmpd with a Group 1 ion Insoluble - most carbonates Insoluble – most phosphates Soluble – hydroxide with Ca+2 Predict solubility of • LiCl • NH4F • Ca(HCO3)2 • BaSO4 • K2CO3 • CaCO3 • Mg3(PO4)2 • Ca(OH)2

Why do we need to predict solubility? • To determine the precipitate in a double replacement reaction

Predicting Products AgNO3(aq) + KCl(aq)  ? AgCl(s) + KNO3(aq)

Table G problems • Shows amount of solute or solvent required for a given amount of the other • Involves setting up a proportion • Precipitation problems

Problem: How much KCl will dissolve in 300 grams of water at 50C? Use the graph to set up a proportion 42 g KCl = 100 g H2O X g KCl 300 g H2O

= Finding amount Solute 42 g KClX g KCl 100 g H2O 300 g H2O X = 126 g KCl

How much H2O is required to just dissolve 200 g NaNO3 at 20C? 88 g NaNO3 = 100 g H2O 200 g NaNO3 X g of H2O

Finding amount H2O 88 g NaNO3 = 200 g NaNO3 100 g H2O X g H2O X = 227.3 g H2O

Precipitation problems • A saturated solution of KNO3 is prepared in 100 g of water at 50C and then cooled down to 10C. How much KNO3 will precipitate?

88 g KNO3 in 100 g H2O at 50C. 20 g KNO3 in 100 g H2O at 10C. 88 g – 20 g = 68 g KNO3 precipitates.

Predicting Solubility of Ionic Compounds in Water: Guidelines and Examples