Mixtures

Classified by size of solute. 3 Types of Mixtures Classified by size of solute.

1)Suspension: Particle size > 1000 nm

Examples - Muddy water Medicines (shake well) Paint

2) Colloid: Particle size between 1 and 1000 nm

Examples - Fog Blood Butter Foam Smoke

3) Solution: *Particles size < 1 nm *Homogeneous

Examples- salt water sugar water pure air alloy (steel)

Particles in a suspension settle out.

Particles in a colloid scatter light, but aren’t visible to the human eye.

Particles in a solution are never visible, and do not scatter light.

The Tyndall Effect Used to distinguish between solutions and colloids.

Solutions

What determines the RATE of solvation? Temperature Agitation Surface area

Aqueous Solutions Water is a “polar” molecule. The O in the molecule has a partial negative charge. The H’s have a partial positive charge. d+ d- O H

Water solvates (surrounds and stabilizes) the ions.

Aqueous Solutions - + Solvation of anion Solvation of cation

What determines solubility? Temperature Pressure (when a gas is involved) Nature of the particles – “Like dissolves like”

Units of Concentration: Percent by Mass % = mass solute x 100 mass solution

Example: What is the percent by mass of NaHCO3 in a solution containing 20g NaHCO3 in 600g H2O?

2. Molarity M = moles solute liters solution

Example - What is the molarity of an aqueous solution containing 40.0g of glucose (C6H12O6) in 1.5 L of solution?

How many moles of NaOH are in 250mL of a 3.0M NaOH solution?

3. Molality m = moles solute kilograms solvent

Example - What is the molality of a solution containing 30.0g of naphthalene (C10H8) dissolved in 500.0g of toluene?

How many grams of water would be needed if 100 g sodium chloride was dissolved to make a 1.35 molal solution?

4. Dilution Allows you to change the concentration of a “stock” solution. M1V1 = M2V2

Example- What volume, in mL, of 2.00 M calcium chloride stock solution would you use to make 0.500 L of 0.300M dilute solution?

5. Mole Fraction XA = molesA total moles

Examples- What is the mole fraction of NaOH in an aqueous solution that contains 22.8% NaOH by mass? An aqueous solution of NaCl has a mole fraction of 0.21. What is the mass of NaCl dissolved in 100.0mL of solution?

Colligative Properties Properties of solutions that are affected by the number of solute particles, but not by their identity.

(it doesn’t matter what is dissolved, only how much!)

1. Vapor Pressure Lowering Vapor pressure is caused by molecules that have evaporated from the surface of a liquid.

Why? When solute is added, particles of solute replace some of the solvent at the surface. This interferes with the ability of solvent to evaporate, reducing vapor pressure.

Also, In a solution the solvent-solute attraction is usually stronger than the original solvent-solvent attraction, further reducing evaporation.

2. Boiling point elevation The difference between the normal boiling point of a pure solvent and the boiling point of a solution.

∆Tb = Kb i m

Kb H2O = 0.51 °C·Kg/mol

example What is the boiling point of a solution of 103.2 g of C6H12O6 in 0.75 Kg of H2O?

What is the molality of a salt water solution that boils at 106.5°C?

3. Freezing point depression The difference between the normal freezing point of a pure solvent and the freezing point of a solution.

∆Tf = Kf i m

Kf H2O = -1.86 °C·Kg/mol

example What is the freezing point of water in a solution of 135.9 g of sucrose (C12H22O11) and 200 g of water?

4. Osmotic Pressure Osmosis – the diffusion of solvent particles across a semipermeable membrane from an area of high solvent concentration to an area of lower solvent concentration. Why is this a colligative property?

Hypotonic cell Hypertonic cell

Π = MRT The average osmotic pressure of blood is 7.7 atm at 25°C. What concentration of glucose, C6H12O6, will be isotonic with blood?