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