Section 8.1 Understanding Reactions in Aqueous Solutions 1.To learn more about some of the results of chemical reactions 2.To learn to predict the solid

Section 8.1

Understanding Reactions in Aqueous Solutions

1. To learn more about some of the results of chemical reactions

2. To learn to predict the solid that forms in a precipitation reaction

3. To learn to write molecular, complete ionic, and net ionic equations

Objectives

Section 8.1


A. Common Results of a Reaction

• Four common events accompany chemical reactions. These often occur when a reaction happens

– Formation of a solid – Formation of water – Formation of a gas

– Transfer of electrons

Can you give examples of each of these?

Section 8.1


B. Precipitation Reactions

What Happens When an Ionic Compound Dissolves in Water?

NaCl (s)H2O NaCl (aq)

But what does NaCl (aq) mean?

NaCl molecules in water ?

Na and Cl atoms in water?

Na+ and Cl- ions in water ?

Section 8.1


• The ions separate and move around independently – a strong electrolyte


What Happens When an Ionic Compound Dissolves in

Water?

Section 8.1


B. A Reaction in Which a Solid Forms

• A reaction in which a solid is formed from a solution is called a precipitation reaction– Solid = precipitate = insoluble

When positive and negative ions form a precipitate the net charge of the precipitate is zero

Pb(NO3)2 (aq) + 2NaI (aq)

PbI2 (s) + 2NaNO3 (aq)

Section 8.1


Stalactites in Yosemite

Ca(HCO3)2(aq)

→ CaCO3(s) +

H2O(l) + CO2(aq)

Section 8.1


Section 8.1



What Happens When Two Ionic Compounds Dissolve in

Water?

• K2CrO4(aq) + Ba(NO3)2(aq) Products

Section 8.1


• Determine the possible products from the ions in the reactants.

• In our example

K2CrO4(aq) + Ba(NO3)2(aq) Products

The possible ion combinations are


How to Decide What Products Form

Section 8.1


What are the potential products in the reactions between the following aqueous solutions? – Write balanced equations for each

• NaOH + CaCl2

• CuBr2 + (NH4)2CO3

• K2SO4 + Fe(NO3)3

Section 8.1



How Would We Decide What Product Has Formed?

• What is most likely to be the yellow solid formed in the following reaction?

K2CrO4(aq) + Ba(NO3)2(aq)

• The possible product combinations are KNO3 and BaCrO4

– KNO3 white solid

– BaCrO4 yellow solid

Section 8.1


B. Precipitation Reactions – Solubility Rules

Section 8.1



• Predicting Precipitates

Using Solubility Rules

– Soluble solid – Insoluble solid – (Slightly soluble solid)

Why are some compounds soluble and others not?

Section 8.1


Solubility Rules – Are These Compounds Soluble or Insoluble?

Barium Nitrate

Potassium Carbonate

Sodium Sulfate

Copper (II) Hydroxide

Mercury (I) Chloride

Ammonium Phosphate

Chromium (III) Sulfide

Lead (II) Sulfate

Section 8.1



Let’s try some predictions: WOC P271 Q10

Section 8.1


C. Describing Precipitation Reactions in Aqueous Solutions

• Three types of equations:– Molecular (formula) equation complete formulas of all reactants and products– Complete ionic equation

all strong electrolytes are shown as ions– Net ionic equation only those components of the solution that undergo a

change• Spectator ion (those that remain unchanged)

not shown in the net ionic equation

Section 8.1



• Molecular Equation

Pb(NO3)2 (aq) + 2NaI (aq)

PbI2 (s) + 2NaNO3 (aq)

• Complete Ionic Equation

Pb2+(aq) + 2NO3

-(aq) + 2Na+

(aq) + 2I-(aq)

PbI2(s) + 2Na+(aq) + 2NO3

-(aq)

Section 8.1



Pb2+(aq) + 2I-

(aq) PbI2(s)

A solution of sodium chloride in water reacts with aqueous silver nitrate to give a precipitate of silver chloride – write down the three equations that describe this reaction and identify the spectator ions

• Net Ionic Equation

• What are the spectator ions in this reaction?

(P272 Q14 – all three equations and identify spectators)

Documents

Section 8.1 Understanding Reactions in Aqueous Solutions 1.To learn more about some of the results of chemical reactions 2.To learn to predict the solid