Bell Work: Colligative Properties 1.Vapor pressure goes ( up / down) with more solute added. 2.Vapor pressure is closely related to ( freezing / boiling ) point. 3.Colligative properties depend on the ( type / number ) of particles. 4.Why does salt melt ice?

Remember: The more solute particles that are in the solution, the more the colligative properties are affected!

Let’s Summarize Ionic Compounds will dissociate and produce electrolytes that are capable of conducting an electric current The following solutes are placed into water. What happens to these solutes as they begin to dissolve?

They dissociate into: NaCl  MgCl 2  Na 3 PO 4  2 moles of ions 3 moles of ions 4 moles of ions 1 Na Cl -1 1 Mg Cl -1 3 Na PO 4 -3 strong electrolyte

Q: Which substance above produces more solute particles in solution? A: Na 3 PO 4 ; therefore, it will have the most influence on colligative properties ***Remember: A colligative property depends on the number of solute particles in solution, not the identity of the particles

Covalent solutes dissolve, but they do NOT dissociate into ions. Why? They do NOT have regions of opposite charge to attract to the nonpolar solvent!

Instead, covalent substances dissolve as whole molecules. The whole molecules form nonelectrolytes and they DO NOT conduct an electric current! nonelectrolyte

The solutes below are placed into water. What happens to these solutes as they begin to dissolve? C 6 H 12 O 6  C 12 H 22 O 11  **They dissociate one molecule at a time! 1 C 6 H 12 O 6 1 C 12 H 22 O 11 1 mole of particles

Q: Which covalent substance above would have the most influence on colligative properties? A: Neither! They would have the same effect b/c each covalent compound produces only ONE mole of solute particle and colligative properties depend on the number of particles!

Let’s Summarize Covalent Compounds will dissociate into only one mole of particles and produce nonelectrolytes that are NOT able to conduct an electric current!

Now it’s your turn! Why do ionic compounds more strongly affect colligative properties than covalent compounds? Ionic compounds always dissociate into two or more particles while covalent compounds always dissociate into only one! Since colligative properties depend on the NUMBER of particles, and ionic compounds produce more particles, they affect colligative properties more!

How does the addition of a solute affect each of the 3 colligative properties? Vapor pressure decreases with addition of solute to solvent! There are solute particles interfering with the solvent particles at the surface of the solution. Less of the solvent can evaporate and push upwards b/c the solute is at the surface, too. Since less solvent is evaporating, vapor pressure drops b/c there is not gas pushing upwards. vapor pressure

Vapor Pressure of a Solution: A Colligative Property Which flask has a lower vapor pressure? Explain. Flask A Flask B Pure Solvent Solution (no solute present) Solute + Solvent

How does the addition of a solute affect each of the 3 colligative properties? Boiling point elevates (increases) with addition of a solute to a solvent. For a substance to boil, atmospheric pressure pushing down must equal vapor pressure pushing up. Solute particles interfere with the solvent particles at the surface.

It will take more energy to get the solvent particles to “push” their way to the surface to evaporate. This means you have to heat the solution up to a higher temperature to give the solvent particles more energy to increase vapor pressure.

How does the addition of a solute affect each of the 3 colligative properties? Freezing point depresses (decreases) with addition of solute to solvent. Solute particles are mixed in with the solvent particles interfering with the ability of solvent particles to “get close” together.

The solute is “in the way.” This means temperature has to drop A LOT for the solvent to push the solute out of the way in order to get close together and solidify.

Ionic Compounds Covalent Compounds polar (have + and – regions ) dissociate into two or more particles at a time ions are called electrolytes conduct electricity strongly affect colligative properties nonpolar (no oppositely charged poles) since no ions, they dissociate one particle at a time no ions so they are called non-electrolytes non-conductors of electricity more weakly affects colligative properties