Colligative Properties

How does the solute change the properties of the solvent? Consider aqueous solutions. Solvent = water. How do the properties of the solution compare to the properties of pure water?

Conductivity Pure water does not conduct electricity. Some solutions do. In order to conduct a current, a solution must contain ions. (MCPs) Conductivity depends on the nature of the particle – Molecular solutes do not conduct.

Colligative Properties Depend on the number of particles in solution not on the type of particles. Doesn’t matter if particles are ions or molecules. Concentration of particles Does matter.

What are some colligative properties? Vapor Pressure Lowering Freezing Point Depression Boiling Point Elevation Osmotic Pressure The higher the concentration of solute particles, the larger the effect.

Does it matter if the solute is ionic or covalent? The number of particles will vary. Ionic solutes will dissolve to produce positive and negative ions  more particles per mole of solute. For covalent solutes, 1-to-1 relationship between moles of solute and moles of dissolved particles.

C6H12O6 Covalent Dissolves as molecules C6H12O6(s)  C6H12O6(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.

MgCl2 Ionic Dissolves as ions MgCl2(s)  Mg2+(aq) + 2Cl-(aq) 1 mole of salt yields 3 moles of ions

As a solute is added to a solvent, what happens to the freezing point & the boiling point of the solution? The freezing point decreases & the boiling point decreases. The freezing point decreases & the boiling point increases. The freezing point increases & the boiling point decreases. 4) The freezing point increases & the boiling point increases.

Which solution containing 1 mole of solute dissolved in 1000 g of water has the lowest freezing point? C2H5OH(aq) NaCl(aq) KOH(aq) 4) CaCl2(aq) Be careful! What if the question asked which solution has the highest freezing point?

Of the following solutions, the one that will freeze at the lowest temperature contains 1 mole of nonvolatile solute dissolved in 1) 250 g of solvent 2) 500 g of solvent 3) 750 g of solvent 4) 1000 g of solvent Lowest fr. pt. means most concentrated.

Which solute, when added to 1000 g of water, will produce a solution with the highest boiling point?  Most concentrated. 29 g of NaCl 58 g of NaCl 31 g of C2H6O2 4) 62 g of C2H6O2 About 1 mole of NaCl. 2 moles of ions. About 1 mole of C2H6O2. 1 mole of molecules.

Which solution will freeze at the lowest temperature? 1 g of NaCl dissolved per 100 g of H2O 1 g of NaCl dissolved per 1000 g of H2O 3) 1 g of C12H22O11 dissolved per 100 g of H2O 4) 1 g of C12H22O11 dissolved per 1000 g of H2O

Which solution will freeze at the lowest temperature? 1) 1 g of NaCl dissolved per 100 g of H2O 1 g  58.8 g/mole = 0.017 moles  0.034 moles of ions. 3) 1 g of C12H22O11 dissolved per 100 g of H2O 1 g  232 g/mole = 0.0043 moles of molecules

Effect of Nonvolatile Solute Boiling Point Elevation Freezing Point Depression The more concentrated the particles, the bigger the effect!

Applications of colligative properties Salting roads in the winter time. Using salted ice to make ice cream.