Unit 4 AP Chemistry Study Guide

WHAT I DID NOT INCLUDE - the 2nd type of phase diagram STUDY IT (pg 5 in notes) -all formulas used (will be provided on the test but familiarize yourself with it) -INTRAMF (covalent,ionic,metallic,etc)

Ion-Dipole

Ionic attracted to polar

• the strength of ion-dipole makes it possible for ionic substances to dissolve in polar solvents

Dipole-Dipole

• molecules with permanent dipoles → attracted to each other

• the positive side of 1 molecule is attracted to the negative end of another molecule

• the more POLAR the molecule → the higher the boiling point

London Dispersion (Shape, Molecular Weight)

• When particles get closer to each other they start to exhibit some attraction

Shape (organics): long, skinny molecules have stronger LD than shorter fat molecules

Weight: Larger atoms have larger electron clouds which are easier to polarize

Which has the greater effect? Comparable size and shape + One larger than another

Comparable size and shape: dipole-dipole and London forces

One larger than another: London dispersion forces will likely determine its physical properties

Increase Trends for IMFS

increase in size

increase in electron density

increase in LD strength

increase in temporary dipole strength

H-Bonds

• extreme dipole-dipole

• when H is bonded to a highly Electronegitative element (FON) because the H bond is exposed to a strong attractive force

Strongest IMF to Weakest

ion-dipole>H-Bond>dipole-dipole>LD

What is Viscosity?

• resistance to flow, related to how molecules move past each other

• flows by sliding molecules past one another

What does viscosity depend on?

1. Attractive forces b/w molecules: Stronger the IMF the higher the viscosity

2. Tendency of molecules to become entangled: More entanglement → greater viscosity

3. Viscosity decreases with an increase in temperature

Surface Tension

Surface molecules are only attracted inward towards the “bulk” molecules → causes a liquid to have a “skin”

• Stronger IMFs → higher surface tension

Cohesive forces

IMFs b/w molecules of the SAME TYPE

Adhesive forces

IMFs b/w molecules of DIFF TYPES

Capillary Action

a process where the liquid rises in a tube bc of a combo of adhesion to the walls of the tube & cohesion b/w the liquid particles

Draw out/Memorize the Phase Change Diagram

A) Soild →B) Freezing/Melting → C) Liquid → D) Condensation/Vaporization → E) Gas

Sublimation (solid→gas)

---

Deposition (gas→solid)

Vapor Pressure

interaction of the molecules on the surface of the liquid that had escaped to a gas and the gas molecules striking the surface and returning to a liquid

• vapor pressure of a liquid is the pressure exerted by the vapor when the liquid and vapor are in dynamic equilibrium

-the pressure of gas becomes constant = dynamic equilibrium

-If equilibrium never established vapor continues to form an eventually the liquid dries out

Liquids that evaporate easily are ________

volatile

Liquids boil when _________________________

the external pressure at the liquid surface = the vapor pressure (norm boiling point is at the standard pressure 1 atm 760 torr, etc)

Temperature of the boiling point increases with ____________

increase in external pressure

Two ways to boil

1. Increase temp

2. Decrease pressure

Solute

• substance that is dissolved in a solvent to form a solution

• typically present in smaller quantities compared to the solvent

Solvent

• a substance capable of dissolving other substances to form a solution.

Solvate

• pulls solute particles apart and surrounds them

Miscible

• 2 liquids dissolved in each other

Immiscible

• 2 liquids that don’t dissolve in each other

Saturated

(as much as it can be)

• hold the most solute at that temp

Unsaturated

(excess)

• at that temp the solvent could hold more

Supersaturated

(rare+unstable)

• holds more than it can actually can at that temp

Factors Affecting Solubility

1. “like dissolves like”

2. more similar IMF → more likely to dissolve

3. gases increase w increase in mass → stronger LD

4. gases increase with increase in pressure

5. solid & liquid increase w temp

6. gas decrease w increase in temp

How to calculate Solution Concentrations in mass percentage

(mass of A in solution)(100)/total mass of solution

How to calculate Solution Concentrations in ppm

(mass of A in solution) (10⁶) / total mass of solution

How to calculate Solution Concentrations in ppb

(mass of A in solution) (10⁹) / total mass of solution

How to calculate Mole Fraction

X(a) = mole of / total moles of solution

What is the mobile phase?

when the liquid/gas is moving up

What is the stationary phase?

the solid/liquid used (separates the mixture)

Gas Chromatography

• separating & analyzing compounds that can be vaporized w/o decomposing

Liquid Chromatography

• separates, identifies, and quantifies components of a mixture (used to find vitamin D lvls in blood)

Paper Chromatography

• separating dissolved chem substances by taking advantage of the diff rates of which they move up the paper

Solvent: non-polar

Paper= polar

What is the Rf Value?

• the distance the sample moves along the paper compared to the overall distance the solvent travels

Gas Characteristics & Pressure

• gas molecules expand to fill their containers

pressure: the amount of force applied to the area P=F/A

Standard Air Pressure

1 atm

760 torr

760 mm Hg

101.3 kPa

Avogadro’s Law

The vol of gas at constant temp & pressure is directly proportional to the # of the moles of the gas PV=nRT

What happens to the density of gas as the gas is heated in a constant-volume container?

no effect

What happens to the density of gas as the gas is compressed at constant temp?

gas density increase & vol decreases

What happens to the density of gas as additional gas is added to a constant-volume container?

gas density increase & greater mass

Kinetic Molecular Theory Part 1

Gases consist of large #s of molecules that are in continuous random motion

Kinetic Molecular Theory Part 2

The combined volume of all molecules of the gas is negligible relative to the total volume which gas is contained

Kinetic Molecular Theory Part 3

Attractive & repulsive forces b/w gas molecules are negligible (gas particles are too far apart so they don’t attract/repulse)

Kinetic Molecular Theory Part 4

Energy transferred b/w molecules during collisions (energy transfers to the one it collides with)

Kinetic Molecular Theory Part 5

The average kinetic energy of the molecules is proportional to the absolute temp

Diffusion

The spread of 1 substance throughout a space or second substance [high(concentration] - [low]

Effusion

The escape of gas molecules through a tiny hole into an evacuated space

Maxwell-Boltzman Curves SAME sub DIFF temp

higher peak = lower temp

lower peak = higher temp

Maxwell-Boltzman Curves DIFF sub SAME temp

higher peak = biggest

lower peak = smallest

Real Gas Traits (all 3)

• Deviate most from ideal gas behavior at extremely high pressure and low temperatures

• All gas particles have some volume bc of the size of their atoms and lengths or their bond

• All gas particles are subject to IMFs

Deviations real gas under ______ circumstances

• non ideal under very high pressure and low temperature

• the more polar a gas it the more the gas will deviate from ideal behavior