Colligative Properties

Objective: – Today I will be able to: Describe the 4 colligative properties of vapor pressure, boiling point, freezing point and osmotic pressure Calculate the Van’t Hoff Factor for a Compound Calculate the freezing point depression and boiling point elevation of a solute Evaluation/Assessment: – Informal Assessment – monitoring student progress as they complete the summary and practice problems – Formal Assessment – analyzing student responses to the activities and exit ticket Common Core Connection – Make sense of problem and persevere in solving them – Look for and make use of structure – Use appropriate tools strategically

Lesson Sequence Evaluate: Warm – Up Explain: BP/FP Homework Review Explain: Colligative Properties Notes Elaborate: Colligative Properties Calculations Evaluate: Exit Ticket

Objective Today I will be able to: Describe the 4 colligative properties of vapor pressure, boiling point, freezing point and osmotic pressure Calculate the Van’t Hoff Factor for a Compound Calculate the freezing point depression and boiling point elevation of a solute

Warm-Up DO NOT SOLVE THIS PROBLEM. Develop a list of steps about how to solve the following Freezing Point Problem Q: What is the expected change in the freezing point of water in a solution of grams of barium nitrate, Ba(NO 3 ) 2, in 4.25 kg of water? (K f = °C/m) ∆T f = K f  m  i

Homework

Agenda Warm-Up BP/FP Homework Review Colligative Properties Notes Part 2 Colligative Properties Calculations Exit Ticket

Boiling Point/Freezing Point Homework Lets review the homework!

Molality Molality (m) = moles of solute/kg of solvent Molality is used for vapor pressure and temperature change Used because it does not change with change in temperature

Important Values

Colligative Properties Notes

Did you know? Some animals are able to survive freezing temperatures by producing natural antifreezes, substances that lower the freezing point of a liquid. In many freeze-tolerant insects, the antifreezes are alcohols and sugars. Examples are box turtles, painted turtles and garter snakes, sugar maples and white spruce.

Volatile? Non-Volatile?? The volatility of a substance refers to the readiness with which it vaporizes Substances with a boiling point below 100 °C are considered volatile and all others are called nonvolatile – Ethyl alcohol and pentane are examples of volatile substances – Sugar and sodium chloride are considered nonvolatile.

Lets Try This Again: Vapor Pressure A solvent in a closed container reaches a state of dynamic equilibrium. The pressure exerted by the vapor in the headspace is referred to as the vapor pressure of the solvent. The addition of any nonvolatile solute (one with no measurable vapor pressure) to any solvent reduces the vapor pressure of the solvent.

Vapor Pressure Nonvolatile solutes reduce the ability of the surface solvent molecules to escape the liquid. – Vapor pressure is lowered. The extent of vapor pressure lowering depends on the amount of solute. – Raoult’s Law quantifies the amount of vapor pressure lowering observed.

Osmosis Some substances form semipermeable membranes, allowing some smaller particles to pass through, but blocking other larger particles. In biological systems, most semipermeable membranes allow water to pass through, but solutes are not free to do so. If two solutions with identical concentration (isotonic solutions) are separated by a semipermeable membrane, no net movement of solvent occurs.

Osmosis Osmosis: the net movement of a solvent through a semipermeable membrane toward the solution with greater solute concentration. In osmosis, there is net movement of solvent from the area of lower solute concentration to the area of higher solute concentration. – Movement of solvent from high solvent concentration to low solvent concentration

Osmosis Osmosis plays an important role in living systems: – Membranes of red blood cells are semipermeable. Placing a red blood cell in a hypertonic solution (solute concentration outside the cell is greater than inside the cell) causes water to flow out of the cell in a process called crenation.

Colligative Properties Placing a red blood cell in a hypotonic solution (solute concentration outside the cell is less than that inside the cell) causes water to flow into the cell. – The cell ruptures in a process called hemolysis.

Colligative Properties - Osmosis Other everyday examples of osmosis: – A cucumber placed in brine solution loses water and becomes a pickle. – A limp carrot placed in water becomes firm because water enters by osmosis. – Eating large quantities of salty food causes retention of water and swelling of tissues (edema).

BP/FP Practice Part 2 Complete the practice. Whatever is not finished in class is homework!

Exit Ticket What is the new freezing point of 200 mL of water (K f = o C) if 195 g of sucrose (C 12 H 22 O 11 ) are added to it? Hint: 1 mL = 1 g