Predicting Solubilities

Net Ionic Equations

•In reactions that occur in solution, write the equation for the reaction in ionic form▫Indicate the ionic species that actually exist

in solution.

BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)

•BaSO4 is an insoluble product (i.e. a precipitate)

•An ionic equation is to break apart aqueous products and reactants ▫BaCl2(aq)

▫Na2SO4(aq)

▫NaCl(aq)

BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)

Ionic Equation:

2Na1+(aq) + SO4

2-(aq) + Ba2+

(aq) + 2Cl1-(aq)

2Na1+(aq) + 2Cl1-

(aq) + BaSO4(s)

Note: BaSO4(s) cannot be broken down

2Na1+(aq) + SO4

2-(aq) + Ba2+

(aq) + 2Cl1-(aq)

2Na1+(aq) + 2Cl1-

(aq) + BaSO4(s)

•Sodium and chloride ions are unchanged and are present on both sides of the equation.▫Since they are not undergoing chemical

reaction, they can be referred to as spectator ions.

•If we subtract the spectator ions from each side of the equation, we then have a net ionic equation.

2Na1+(aq) + SO4

2-(aq) + Ba2+

(aq) + 2Cl1-(aq)

2Na1+(aq) + 2Cl1-

(aq) + BaSO4(s)

•The net ionic equation for the above reaction is:

Ba2+(aq) + SO42-

(aq) -----> BaSO4(s)

•Note: You must pay attention to reactions that occur. ▫Use the solubility tables that you copied in

the last unit to determine whether the reaction will occur

▫Consider if the reactions are single displacement or double displacement

Example•Write the net ionic reaction. Be sure to

include charges on ions.

K2CrO4(aq) +Ba(NO3)2(aq) → 2KNO3 (aq)+ BaCrO4(s)

Learning Check•Write the net ionic reaction. Be sure to

include charges on ions.KCl(aq) + AgNO3(aq) → KNO3(aq) + AgCl(s)

Learning Check•Write the net ionic reaction. Be sure to

include charges on ions.

3KOH(aq) + Fe(NO3)3(aq) → 3KNO3 (aq) + Fe(OH)3(s)

Solubility Curves

•Solubility curves, like the one shown here, tell us what mass of solute will dissolve in 100g (or 100mL) of water over a range of temperatures.

•The solutions are saturated at the given temperatures.

Example:• What mass of solute

will dissolve in 100mL of water at the following temperatures.

1. KNO3at 70°C  

2. NaCl at 100°C  

3. NH4Cl at 90°C

Example:•Which of the three

substances is most soluble in water at 15°C.

1. KNO3at 70°C  

2. NaCl at 100°C  

3. NH4Cl at 90°C

Example:• State whether the

following solutions are saturated, unsaturated or supersaturated

1. 100 g of KNO3at 60°C

 

2. 30 g of NaCl at 80°C  

3. 80g of NH4Cl at 90°C

•You'll notice that for most substances, solubility increases as temperature increases.

•In solutions involving liquids and solids typically more solute can be dissolved at higher temperatures.

•There are exceptions to this rule, however, we will not get into them in this course.

Homework

•Solubility Curve Worksheet

Concentration of a Solution from the Mass of the Precipitate

•A student carefully measured 100 mL of a silver nitrate solution, AgNO3(aq), of unknown concentration and added a copper coil. When the reaction was complete, the solution was filtered to obtain all the silver. The dry precipitate had a mass of 1.65 g. What was the molar concentration of the silver nitrate solution?

Limiting Reactants and Precipitates

In water purification, aluminum sulfate, Al2(SO4)3(aq), reacts with calcium hydroxide, Ca(OH)2(aq), to form a precipitate of aluminum hydroxide, Al(OH)3(s).

a) Write a balanced equation.

b) Find the mass of aluminum hydroxide that precipitates when 20.0 mL of 0.0150 mol/L aluminum sulfate is mixed with 30.0 mL of 0.0185 mol/L aqueous calcium hydroxide.

Minimum Volume for a Complete Reaction A kidney stone contains primarily

calcium oxalate, CaC2O4(s). A chemist wants to react 60.0 mL of 0.135 mol/L sodium oxalate, Na2C2O4(aq), with 0.226 mol/L calcium chloride, CaCl2(aq), to precipitate calcium oxalate.

a) Write a balanced equation.

b) What mass of calcium oxalate will be precipitated?

c) What is the minimum volume of calcium chloride solution required?

Homework

•Pg 417 Q 12, 13, 14•Pg 420 Q 21 , 22