Colligative properties depend on the number of solute particles in a solution. Section 4: Colligative Properties of Solutions K What I Know W What I Want to Find Out L What I Learned

10(E) Distinguish between types of solutions such as electrolytes and nonelectrolytes and unsaturated, saturated, and supersaturated solutions. 2(I) Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology–based reports. 3(A)In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. Colligative Properties of Solutions Copyright © McGraw-Hill Education

Essential Questions What are colligative properties? What are four colligative properties of solutions? How are the boiling point elevation and freezing point depression of a solution determined? Colligative Properties of Solutions Copyright © McGraw-Hill Education

Review ion Colligative Properties of Solutions Copyright © McGraw-Hill Education Vocabulary New colligative property vapor pressure lowering boiling point elevation freezing point depression osmosis osmotic pressure

Colligative Properties of Solutions Copyright © McGraw-Hill Education Electrolytes and Colligative Properties Colligative properties are physical properties of solutions that are affected by the number of particles but not by the identity of dissolved solute particles. Colligative means depending on the collection Colligative properties include: vapor pressure lowering, boiling point elevation, freezing point depression and osmotic pressure.

Colligative Properties of Solutions Copyright © McGraw-Hill Education Electrolytes and Colligative Properties Ionic compounds are electrolytes because they dissociate in water to form a solution that conducts electricity. Electrolytes that produce many ions are strong electrolytes. Electrolytes that produce only a few ions are weak electrolytes. Many molecular compounds do not ionize when dissolved, and do not conduct electricity, these are called nonelectrolytes. There are some exceptions, so those molecular compounds that do ionize are electrolytes.

Colligative Properties of Solutions Copyright © McGraw-Hill Education Vapor Pressure Lowering Vapor pressure lowering is due to the number of solute particles in solution and is a colligative property of solutions. Adding a nonvolatile solute (one that has little tendency to become a gas) to a solvent lowers the solvent’s vapor pressure. When a solute is present, a mixture of solvent and solute occupies the surface area, and fewer particles enter the gaseous state. The greater the number of solute particles, the lower the vapor pressure.

Colligative Properties of Solutions Copyright © McGraw-Hill Education Boiling Point Elevation The temperature difference between a solution’s boiling point and a pure solvent's boiling point is called the boiling point elevation. When a nonvolatile solute lowers the vapor pressure of a solvent, the boiling point is also affected. More heat is needed to supply additional kinetic energy to raise the vapor pressure to atmospheric pressure.

Colligative Properties of Solutions Copyright © McGraw-Hill Education Boiling Point Elevation

Colligative Properties of Solutions Copyright © McGraw-Hill Education Freezing Point Depression A solution's freezing point depression is the difference in temperature between its freezing point and the freezing point of the pure solvent. At a solvent's freezing point temperature, particles no longer have sufficient kinetic energy to overcome interparticle attractive forces. The freezing point of a solution is always lower than that of the pure solvent. Solute particles interfere with the attractive forces among solvent particles.

Colligative Properties of Solutions Copyright © McGraw-Hill Education Freezing Point Depression

Colligative Properties of Solutions Copyright © McGraw-Hill Education Freezing Point Depression

Colligative Properties of Solutions Copyright © McGraw-Hill Education CHANGES IN BOILING AND FREEZING POINTS Use with Example Problem 6. Problem Sodium chloride (NaCl) is often used to prevent icy roads and to freeze ice cream. What are the boiling and freezing points of a 0.029m aqueous solution of sodium chloride? Response ANALYZE THE PROBLEM You are given the molality of an aqueous sodium chloride solution. First, calculate ΔT b and ΔT f based on the number of particles in the solution. Then, to determine the elevated boiling point and the depressed freezing point, add ΔT b to the normal boiling point and subtract ΔT f from the normal freezing point of water. KNOWNUNKNOWN molality of solution = 0.029m boiling point = ?°C Kb = 0.512°C/mfreezing point = ?°C Kf = 1.86°C/m SOLVE FOR THE UNKNOWN Determine the molality of the particles. particle molality = 2 × 0.029m = 0.058m Determine ΔT b and ΔT f State the boiling point elevation and freezing point depression formulas. ΔT b = K b m ΔT f = K f m

Colligative Properties of Solutions Copyright © McGraw-Hill Education CHANGES IN BOILING AND FREEZING POINTS EVALUATE THE ANSWER The boiling point is higher and the freezing point is lower, as expected. Because the molality of the solution has two significant figures, both ΔT b and ΔT f have two significant figures. Because the normal boiling point and freezing point are exact values, they do not affect the number of significant figures in the final answer. SOLVE FOR THE UNKNOWN (continued) Substitute K b = 0.512°C/m, K f = 1.86°C/m, and m = 0.058m. ΔT b = (0.512°C/m)(0.058m) = 0.030°C ΔT f = (1.86°C/m)(0.058m) = 0.11°C Determine the elevated boiling point and depressed freezing point of the solution. Add ΔT b to the normal boiling point and subtract ΔT f from the normal freezing point. boiling point = °C °C = °C freezing point = 0.00°C °C = -0.11°C

Colligative Properties of Solutions Copyright © McGraw-Hill Education Osmotic Pressure Osmosis is the diffusion of a solvent through a semipermeable membrane. Osmotic pressure is the amount of additional pressure caused by water molecules that moved into the concentrated solution.

Colligative Properties of Solutions Copyright © McGraw-Hill Education Review Essential Questions What are colligative properties? What are four colligative properties of solutions? How are the boiling point elevation and freezing point depression of a solution determined? Vocabulary colligative property vapor pressure lowering boiling point elevation freezing point depression osmosis osmotic pressure