Section 8.1Water and Chemical ReactionsThe reactions that are most important to
us happen in water. Ex.: Metabolic reactions happen in a watery
environment (inside or outside cells) Ex.: Oxygen dissolves in blood (mostly
water) and binds to hemoglobin on red blood cells so it can be distributed to body cells; oxygen is used to release energy from food in a series of reactions.
Copyright© by Houghton Mifflin Company. All rights
reserved. 2
What are the driving forces that cause chemical reactions to happen?
Several “tendencies” drive reactants to form products:
Formation of a solid Formation of water Transfer of electrons Formation of a gas
Formation of a Solid:Precipitation Reaction A solid forms new substance
formed chemical reaction has happened
A common form of precipitation is the formation of a solid ionic compound from a mixture of two aqueous compounds
The solubility of the new compound determines whether a precipitate forms
Copyright© by Houghton Mifflin Company. All rights reserved. 4
Formation of solid AgCl (precipitation)Formation of solid AgCl (precipitation)from a mixture of KCl and AgNOfrom a mixture of KCl and AgNO33
Solid/powder = precipitate
Copyright© by Houghton Mifflin Company. All rights reserved. 5
1. Ions from an ionic compound dissociate (separate) when mixed in water.2. A new combination of ions (cation and anion) may form.3. If the new compound is insoluble in water, it will precipitate
as a solid.
Possible Ion Combinations (not in notes):Possible Ion Combinations (not in notes):
Copyright© by Houghton Mifflin Company. All rights reserved. 6
Cl- NO3-
K+ KCl KNO3
Ag+ AgCl AgNO3
Reactants:Reactants:KCl and KCl and AgNO3
Possible new compounds:Possible new compounds:AgCl and KNO3
Which of these is insoluble in water?
Copyright© by Houghton Mifflin Company. All rights reserved. 7
Using Using solubility solubility
rules:rules:
Solubilities Solubilities of common of common compoundscompounds
8
Predicting the Products of a Precipitation Reaction
1. Write proper, neutral formulas -- consider the products that could form by exchanging the ions of the added salts;
2. Balance the equation using coefficients;
3. Add physical states -- use the solubility rules to decide whether a solid forms and predict its identity.
Equations Used to Describe a Precipitation Reaction
Ex.: Precipitation of Silver Chloride
Molecular Equation – shows overall reaction with molecular formulas:
AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
Complete Ionic Equation – shows strong electrolytes (aq) as ions:
Ag+(aq) + NO3
- (aq) + K+
(aq) + Cl- (aq) AgCl(s) + K+ (aq) + NO3
-(aq)
Net Ionic Equation – shows only the components that form the precipitate; spectator ions are not shown:
Ag+(aq) + Cl- (aq) AgCl(s)
Top Related