Topic: Colligative Properties

Adding a non-volatile (doesn’t readily evaporate) solute affects… Conductivity (electrolytes) Freezing point Boiling point Vapor pressure

Freezing Point Depression Adding solute will lower the freezing point Which one will lower the freezing point more? – NaCl or MgCl 2 – Na +1 (aq) + Cl -1 (aq) Mg +2 (aq) + 2Cl -1 (aq) – 1 mol + 1 mol = 2 moles 1 mol + 2 mol = 3 moles

Vapor Pressure Decreased Solute particles at the surface get in the way of some solvent molecules evaporating

Boiling Point Elevation Adding solute will raise the boiling point Which one will raise the boiling point more? – Sugar (C 12 H 22 O 11 ) or salt (NaCl) – C 12 H 22 O 11 (aq) Na +1 (aq) + Cl -1 (aq) – 1 mol 1 mol + 1mol = 2 moles

Boiling Point Freezing Point Vapor Pressure

Depends on the # of moles dissolved in the solution and NOT on the type of particles The higher the concentration of solute in solvent, the more MP, BP, and VP are affect

Which solution containing 1 mole of solute dissolved in 1000 g of water has the lowest freezing point? 1)C 2 H 5 OH(aq) 2)NaCl(aq) 3)KOH(aq) 4) CaCl 2 (aq) Be careful! What if the question asked which solution has the highest freezing point?

C 6 H 12 O 6 Covalent Dissolves as molecules C 6 H 12 O 6 (s)  C 6 H 12 O 6 (aq) 1 mole of sugar yields 1 mole of molecules

NaCl Ionic Dissolves as ions NaCl(s)  Na + (aq) + Cl - (aq) 1 mole of salt yields 2 moles of ions. Get more particles from salt than sugar.

MgCl 2 Ionic Dissolves as ions MgCl 2 (s)  Mg 2+ (aq) + 2Cl - (aq) 1 mole of salt yields 3 moles of ions