Chapter 8 Solutions 8.3 Solubility

Solubility Solubility is the maximum amount of solute that dissolves in a specific amount of solvent expressed as grams of solute in 100 grams of solvent (usually water): g of solute 100 g water

Unsaturated Solutions contain less than the maximum amount of solute can dissolve more solute Dissolved solute

Saturated Solutions Saturated solutions contain the maximum amount of solute that can dissolve some undissolved solute at the bottom of the container Dissolved solute Undissolved solute

Learning Check At 40 C, the solubility of KBr is 80 g/100 g of H2O. Identify the following solutions as either (S) saturated or (U) unsaturated. Explain. A. 60 g KBr added to 100 g of water at 40 C. B. 200 g KBr added to 200 g of water at 40 C. C. 25 g KBr added to 50 g of water at 40 C.

Solution A. U 60 g of KBr/100 g of water is less than the solubility of 80 g of KBr/100 g of water. B. S 200 g KBr added to 200 g of water at 40 C. This is the same as 100 g of KBr in 100 g of water, which is more than the solubility of 80 g of KBr/100 g of water at 40 C. C. U 25 g KBr added to 50 g of water at 40 C. This is the same as 50 g of KBr in 100 g of water, which is less than the solubility of 80 g of KBr/100 g of water at 40 C.

Effect of Temperature on Solubility depends on temperature of most solids increases as temperature increases of gases decreases as temperature increases

Solubility and Pressure Henry’s law states: the solubility of a gas in a liquid is directly related to the pressure of that gas above the liquid at higher pressures, more gas molecules dissolve in the liquid

Learning Check A. Why could a bottle of carbonated drink possibly burst (explode) when it is left out in the hot sun? B. Why do fish die in water that is too warm?

Solution A. Why could a bottle of carbonated drink possibly burst (explode) when it is left out in the hot sun? The pressure in a bottle increases as the gas leaves solution as it becomes less soluble at high temperatures. As pressure increases, the bottle could burst. B. Why do fish die in water that is too warm? Because O2 gas is less soluble in warm water, fish cannot obtain enough O2 to survive.

Soluble and Insoluble Salts Ionic compounds that dissolve in water are soluble salts do not dissolve in water are insoluble salts

Solubility Rules Soluble salts typically contain at least one ion from Groups 1A(1), NO3−, or C2H3O2− (acetate). Most other combinations are insoluble.

Examples of Using the Solubility Rules

Learning Check Use the solubility rules to determine if each salt is (S) soluble or (I) insoluble. Explain. A. Na2SO4 B. MgCO3 C. PbCl2 D. MgCl2

Solution A. Na2SO4 (S) soluble; contains Na+ B. MgCO3 (I) insoluble; contains carbonates C. PbCl2 (I) insoluble; insoluble chloride D. MgCl2 (S) soluble; only chlorides of Pb2+, Ag+, and Hg22+ are insoluble

Formation of a Solid When solutions of salts are mixed, a solid forms if ions of an insoluble salt are present Example: AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

Equations for Forming Solids A full equation shows the formulas of the compounds. Pb(NO3)(aq) + 2NaCl(aq) PbCl2(s) + 2NaNO3(aq) An ionic equation shows the ions of the compounds. Pb2+(aq) + 2NO3−(aq) + 2Na+(aq) + 2Cl−(aq) PbCl2(s) + 2Na+(aq) + 2NO3−(aq) A net ionic equation shows only the ions that form a solid. Pb2+(aq) + 2Cl−(aq) PbCl2(s)

Guide to Writing New Ionic Equations for an Insoluble Salt

Finding the Insoluble Salt STEP 1 Write the ions of the reactants. Ba2+(aq) + 2NO3−(aq) + 2Na+(aq) + CO32−(aq) STEP 2 Write the new combinations of the ions and determine if an insoluble salt forms. BaCO3(s) + 2Na+(aq) + 2NO3−(aq) STEP 3 Write the ionic equation, including the insoluble salt as a solid in the products. Ba2+(aq) + 2NO3−(aq) + 2Na+(aq) + CO32 −(aq) BaCO3(s) + 2NO3−(aq) + 2Na+(aq) STEP 4 Write the net ionic equation deleting spectator ions. Ba2+(aq) + CO32−(aq) BaCO3(s)

Learning Check Write the formula of an insoluble salt, if any, and the net ionic equation for each of the following mixtures: A. BaCl2(aq) + Na2SO4(aq) ? B. AgNO3(aq) + KCl(aq) ? C. KNO3(aq) + NaCl(aq) ?

Solution BaSO4(s) Ba2+(aq) + SO42−(aq) BaSO4(s) A. BaCl2(aq) + Na2SO4(aq) ? BaSO4(s) Ba2+(aq) + SO42−(aq) BaSO4(s) B. AgNO3(aq) + KCl(aq) ? AgCl(s) Ag+(aq) + Cl−(aq) AgCl(s) C. KNO3(aq) + NaCl(aq) ? None; all combinations of ions are soluble salts.