Aim: How does the addition of a solute affect the colligative properties of the solvent? Do Now: In pairs compare answers to HW.

Molecules vs. Ionic Compounds in Aqueous solutions Some molecular compounds dissolve but do not dissociate into ions. C6H12O6(s) (glucose)  C6H12O6 (aq) 1 mole of solid sugar gives 1 mole of dissolve sugar in water

Molecules vs. Ionic Compounds in Aqueous solutions Many ionic compounds dissociate into independent ions when dissolved in water NaCl (s)  Na+(aq) + Cl-(aq) 1 mole of NaCl solid gives 1 mole of sodium ions and 1 mole of chloride ions when dissolves (total of 2 moles of dissolved particles). MgCl2 (s)  Mg+2(aq) + 2Cl-(aq) Total of 3 moles of dissolved particles

Why do you think salt is added to icy roads? Salting roads works by altering the freezing point of water. Water with a higher salt content has a lower freezing point than water with less salinity. Salting icy roads and walkways lowers the freezing point of the water that forms ice which leads to melting and prevents falling snow or rain from being able to freeze.

Colligative Properties Colligative properties refers to properties of a solution that depend on the concentration of particles. Boiling point Freezing point

How does concentration solution effect boiling point? What is the boiling point of the solvent when there is no solute? What happens to the boiling point for any given solution as more solute is dissolved? CONCENRATION

How does concentration of a solution affect freezing point? What is the freezing point of the solvent when there is no solute present? What happens to the freezing point for any given solution as there is more solute dissolved?

Effects Of Adding Solutes to Water The addition of solutes to water: Raises boiling point Lowers freezing point The more moles of particles dissolved the greater change it has on the colligative properties.

Boiling Point Elevation The presence of a nonvolatile solute (salt or sugar) raises the boiling point of the solvent. Nonvolatile: does not easily vaporize The greater the concentration ( more moles of dissolved particles)of the solute, the more it raises the boiling point.

Freezing Point Depression The presence of any solute (salt or sugar) lowers the freezing point of the solvent. The more moles of dissolved particles (greater concentration of solute), the lower the freezing point.

How does the type of solute, ionic or molecular, affect boiling point and freezing point? The elevation of the boiling point or depression of freezing point depends on the number of mols of particles present. Ionic solutes have a greater affect on the colligative properties compared to molecular solutes

Which of the following substance would increase the boiling point of water the most? Explain.