CHAPTER 4: Types of Chemical Reactions

[Pages:39]CHAPTER 4: Types of Chemical Reactions

?Dissolution ?Precipitation ?Acids and Bases and their reactions ?Oxidation-Reduction Reactions

CHEM 1310 A/B Fall 2006

Dissolution of Ionic Compounds

CHEM 1310 A/B Fall 2006

Dissolution of Molecules

CHEM 1310 A/B Fall 2006

Electrolytes

? Substances which increase the conductivity of water when they dissolve

? Usually ionic compounds (e.g., NaCl), but some molecules can also dissolve into ions (e.g., acids like HCl, HNO3). Strong bases can also be electrolytes (NH3 can split H2O into ions).

CHEM 1310 A/B Fall 2006

Solubility

? Tells how much of something (the "solute") will dissolve into a given solvent

? Example: incomplete dissolution of sugar in iced tea

? Observation: hot tea dissolves sugar much easier than iced tea. This implies...

? Another observation: Coke goes flat faster at higher temperatures. Why? Solubility of gases change ...

CHEM 1310 A/B Fall 2006

Rules about solubility

? Most general rule: "Like dissolves like"

? Polar solvents (water, methanol, etc) usually dissolve polar molecules and ionic substances; nonpolar solutes not very soluble

Polar ethylene glycol dissolves in water

? Nonpolar solvents (CCl4, benzene, etc) usually dissolve nonpolar molecules; don't dissolve polar molecules well

Oil and water do not mix

CHEM 1310 A/B Fall 2006

More rules about solubility

? No gases or solids are infinitely soluble ("miscible in all proportions") with water; many liquids are

? Common inorganic acids soluble in water; organic acids which are small molecules soluble in water

? Small organic compounds with ?OH and ?NH2 groups usually soluble in water

? Gases are less soluble as temperature increases. Liquids and soluds usually more soluble as temperature increases

? Solubilities of ionic compounds varies in water; see Table 4-1

CHEM 1310 A/B Fall 2006

Precipitation Reactions

? Opposite of dissolution --- a solid comes out of solution Na+ (aq) + Cl- (aq) NaCl(s)

? Can cause precipitation by (a) lowering temperature (e.g., "rock candy"), (b) evaporating solvent, (c ) mixing 2 or more solutions, e.g, BaCl2 (aq) + K2SO4 (aq) BaSO4 (s) + 2 KCl (aq) all of these are quite soluble in water except BaSO4

Precipitation of lead iodide, PbI2, from KI (aq) + Pb(NO3)2 (aq)

CHEM 1310 A/B Fall 2006

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download