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) – Na 2 CO 3(s)  2 Na + (aq) + CO 3 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

Homework Pg. 389 # 1 – 8, 12, 15