Chapter 4; Reactions in Aqueous Solutions

I. Electrolytes vs. NonElectrolytes

II. Precipitation Reactiona) Solubility Rules

4.1

A solution is a homogenous mixture of 2 or more substances

The solute is(are) the substance(s) present in the smaller amount(s)

The solvent is the substance present in the larger amount

In aqueous solutions (aq)*solvent is water*solute can be ionic compounds, aqueous acids, bases, or molecular compounds

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.

A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.

nonelectrolyte weak electrolyte strong electrolyte4.1

Soluble Salts - substances which result from the neutralization of an acid by a base and are soluble in water are of interest - since they dissociate in water to give separate ions

NaCl(aq) Na+(aq) + Cl- (aq)

CaCl2(aq) Ca2+(aq) + 2 Cl- (aq)

C12H22O11(aq) C12H22O11(aq)

molecules stay intact - nonelectrolyte

**The formation of an insoluble solid (a precipitate) drives a chemical reaction.**For these reactions we can write three kinds of equations.

MOLECULAR, IONIC, AND NET IONIC EQUATIONS

a) Molecular Equations-complete formulas are written for all the reactants and products, no ions are written.b) Ionic equations-all strongly soluble electrolytes are written in their dissociated (ionized) forms.

c) Net Ionic equations-only involve those chemical species which are involved in a chemical reaction. All spectator ions are eliminated.Spectator ions-those ions which do not participate in the chemical reaction but are present in the reaction mixture.

Write the molecular, ionic, and net ionic equations for the reaction of an aqueous solution of CaCl2 and an aqueous solution of Na2CO3.

4.1

Strong Electrolyte

Weak Electrolyte Nonelectrolyte

Strong Acids Weak Acids Molecular Compounds

Strong Bases Weak Bases

Ionic Compounds

Electrolytic Solutions Contain Mobile Cations (+) and Anions(-)

• Ionic Compounds, Aqueous Acids, and Base Dissociate Into the Ions They are Made of When Dissolved in Water.

NaCl (s) Na+ (aq) + Cl-(aq)

• More Ions in Solutions; Stronger Electrolyte

H2O

Strong Electrolyte – 100% dissociation

HCl (g) H+ (aq) + Cl- (aq)H2O

Weak Electrolyte – not completely dissociated

Weak vs. Strong ElectrolyteA strong electrolyte will produce more ions

when same amount of solid is dissolved in solvent.

HNO2 NO2- (aq) + H+ (aq)

H2O

H+ Cl-

H+

Cl-

H+ NO2-

H+NO2-

Precipitation Reactions

• Mix two aqueous solutions made by dissolving ionic compounds in water.

• If a reaction happens, a precipitate (solid) is formed.

Predicting Products of Precipitation Reactions

1) Ionic Compounds are Strong Electrolytes –Determine charge on all ions of reactants

2) Using Ion Charges; Predict formula of products. ( + ion of one reactant forms compound with – ion of other reactant)

3) Balance Equation4) Determine is product is solid or aqueous

solution

Solubility Rules for Common Ionic CompoundsIn water at 250C

Soluble Compounds ExceptionsCompounds containing alkali metal ions and NH4

+

NO3-, HCO3

-, ClO3-

Cl-, Br-, I- Halides of Ag+, Hg22+, Pb2+

SO42- Sulfates of Ag+, Ca2+, Sr2+, Ba2+,

Hg2+, Pb2+

Insoluble Compounds Exceptions

CO32-, PO4

3-, CrO42-, S2- Compounds containing alkali

metal ions and NH4+

OH- Compounds containing alkali metal ions and Ba2+

4.2

Predicting Products of Precipitation Reactions (Cont)

5) Determine spectator ions (Ions that are still dissolved in water in the product)

6) Write net ionic equation (Only shows ions involved in forming solid)

1) the molecular equation is: CaCl2(aq) + Na2CO3(aq) CaCO3(s)+2NaCl(aq)

2) the ionic equation is: Ca2+

(aq) + 2 Cl-(aq) + 2 Na+

(aq) + CO32-

(aq) CaCO3(s) + 2 Na+

(aq) + 2 Cl-(aq)

3) the net ionic equation is: Ca2+

(aq) + CO32- (aq) CaCO3(s)

Precipitation Reactions

Precipitate – insoluble solid that separates from solution

molecular equation

ionic equation

net ionic equation

Pb2+ + 2NO3- + 2Na+ + 2I- PbI2 (s) + 2Na+ + 2NO3

-

Na+ and NO3- are spectator ions

PbI2

Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)

precipitate

Pb2+ + 2I- PbI2 (s)

4.2

AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)

Ag+ + NO3- + Na+ + Cl- AgCl (s) + Na+ + NO3

-

Ag+ + Cl- AgCl (s)4.2

Write the net ionic equation for the reaction of silver nitrate with sodium chloride.