Solutions & The Dissolving Process

LG: I can explain the behaviour of molecular and ionic compound in water

Forces at Work• Inter- and intramolecular forces can be used

to explain many of the properties of solutions• Intramolecular forces– Covalent bonds– Ionic bonds

• Intermolecular forces– Dipole-Dipole– London Dispersion– Hydrogen bonds

What makes water so special?

• It is often called the “universal solvent”• Many substances, but not all, dissolve in water

• Water is a good solvent for 3 reasons:– Small size – polar– Capable of hydrogen bonding

Ionic Solutes in Water• Ionic compounds have strong bonds and high melting

points but tend to dissolve easily in water– Positive hydrogen atoms

are attracted to anions in ionic compounds

– Negative oxygen atoms are attracted to cations in ionic compounds

– The process of ions separating from a crystal is called dissociation

– Ex. NaCl(s) Na+(aq) + Cl-

(aq)

– Na2CO3(s) 2 Na+(aq) + CO3

2-(aq)

Hydration

Molecular Solutes in Water• Molecular compounds vary in their ability to dissolve

in water; it depends on whether the molecule is polar and capable of hydrogen bonding

• If a molecular compound dissolves, the molecule remains intact

Molecular Solutes (cont)

• Liquids that mix easily are said to be ‘miscible’– Water and ethanol mix easily

because both are polar and capable of hydrogen bonds

• Liquids that do not mix easily are ‘immiscible’– Oil and water do not mix because water

molecules are more strongly attracted to each other

“Like Dissolves Like”

Surfactants & Emulsifiers• Surfactants and emulsifiers both contain a polar end

and a non-polar end which help molecules with different polarity mix– Surfactants (for cleaning): soaps and detergents– Emulsifiers (for cooking): egg and mustard

Activity: Psychedelic Milk!

• Materials:– Detergent, milk, plate, food colouring, Q-tips

• Instructions:– Add about 1cm of milk to the dish– Put a few drops of different colours of food

colouring onto 3 spots on the surface of the milk– Dip a Q-tip in detergents and place it somewhere

in the milk

HomeworkPg. 389 # 1 – 8, 12, 15