UNIT IXLesson #3

Like dissolves like! (Miscibility)

Polar Vs Non-Polar

nonpolar = symmetrical polar = asymmetrical

(if one end of the molecule differs from the other)

Methane Hydrogen fluoride

Which compounds dissolve in what??

Experimentally, it is found that…“LIKE DISSOLVES LIKE”

POLAR dissolves ------- POLAR ------- IONIC

  NONPOLAR dissolves ------- NONPOLAR

*Miscible = soluble

EXAMPLES

EX#1: WATER AND CARBON TETRACHLORIDE

EXAMPLES

EX#2: IODINE IN WATER

EXAMPLES

EX#3: IODINE IN CARBON TETRACHLORIDE

EXAMPLES

EX#4: SUGAR IN WATER

EXAMPLES

EX#5: SUGAR IN CARBON TETRACHLORIDE

EXAMPLES

EX#6: ETHANOL, CH3CH2OH

Ethanol in water Ethanol in carbon tetrachloride

METHANOL & ETHANOL

CH3OH CH3CH2OH

WHICH ONE DO YOU THINK IS SLIGHTLY BETTER AT DISSOLVING NON-POLAR COMPOUNDS?

Common solvents: p.204

Water- the most common polar solvent… Methanol (polar and non-polar ends) Ethanol (polar and non-polar ends) benzene ethoxyethane Acetone ( polar and non polar ends) acetic acid Chloroform carbon tetrachloride (non-polar) heptane liquid ammonia

DISSOLVING PROCESS

http://www.northland.cc.mn.us/biology/biology1111/animations/dissolve.html

Why can’t non-polar solvents dissolve ionic compounds?

Non-polar solvents can only attach to solutes using London forces; these forces cannot overcome the strong bonds that hold ionic compounds together

Ionic solutes are held by very strong ionic bonds when they are in the solid phase, so they need the most polar solvent, such as water, to dissolve them.

HOMEWORK

Hebden p. 207

# 18, 19, 20, 22

Hebden p. 208

# 23 (be careful if they are asking for inter or intra molecular forces)

#24 ( determine the forces that exist first between the molecules, to decide which is stronger. The stronger= the higher the melting point)

#25