SCH3U Unit 3 Solutions and Solubility

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					SCH3U Unit 3: Solutions and Solubility
Mr. Krstovic November 18, 2005

Defining Solutions
 Solutions are homogeneous mixtures of substances composed of at least one SOLUTE and one SOLVENT.  SOLUTE: a substance that is dissolved in a solvent (eg. NaCl)  SOLVENT: the medium in which a solute is dissolved (eg. Water)  AQUEOUS SOLUTIONS have water as the solvent

Classification of Solutions
 Please take a look at Table 1 p.266. PLEASE DO NOT COPY THIS – It’s in your textbook.  Gas in Gas: Oxygen in nitrogen (air)  Gas in Liquid: Oxygen in water  Gas in Solid: Oxygen in ice  Liquid in Gas: Water in air  Liquid in Liquid: Methanol in water  Liquid in Solid: Hg in Ag  Solid in Liquid: Sugar in water  Solid in Solid: Sn in Cu (bronze)

Explaining Solutions
 Why do some chemicals dissolve in water?  Why are some chemicals mutually attracted to each other?  Recall the following concepts:
INTRAmolecular forces (i.e. covalent) INTERmolecular forces - London Forces (between all molecules including nonpolar molecules) - Dipole- Dipole (in polar molecules) - H- bonding (between H and O, N, or F)

Let’s Revisit Polar and Non polar Molecules First

Guidelines for Predicting Polar Molecules
 AB = any diatomic compound is polar (eg. CO)  HAx = any molecule with a single H (eg. HCl, HBr)  AxOH = any molecule with an OH at one end (eg. C2H5OH)  OxAy = any molecule with an O at one end (eg. H2O, OCl2)  NxAy = any molecule with an N at one end (eg. NH3, NF3)

Non-polar substances
 Non polar substances have an equal distribution of charge and interact with other nonpolar substances because of London (dispersion) force interactions.  Guidelines for predicting non-polar substances: Ax = all elements (Cl2, N2) CxAy = most carbon compounds (including organic solvents, fats and oils) CO2, CH4

Using your guidelines which of the following molecules are polar and which are non-polar ?
       HBr NCl3 CCl4 HC2H3O2 C3H7OH N2 C6H6

 London Dispersion Forces – temporary displacement of the electron cloud; exist between all molecules

Dipole-Dipole Forces
 Attractive forces that exist between POLAR molecules

Hydrogen Bonding
 H attracts O, F or N

H Bonding in Water

Molecular Substances in Water
 Polar substances dissolve in other polar substances  Nonpolar substances dissolve in nonpolar substances  In other words, “like dissolves like”

Which of the following will be soluble in water? Explain using structural representation.

 Dissociation: separation of ions that occurs when an ionic compound, such as table salt (NaCl), dissolves in water. IONIC EQUATION:
NaCl (s)→ Na+(aq) + Cl –(aq)

Homework Questions
 Read Section 6. 2  Answer Questions 1, 2 and 3 p.280