4B Chapter 13 Notes

Stephanie Hutchinson Tre Jennings Dissociation Stephanie Hutchinson Tre Jennings

Dissociation Dissociation: The separation of ions that occurs when an ionic compound dissolves. Chemical equations in dissociation require balanced charge as well as atoms. For now, 100% dissociation can always be assumed.

Example The dissociation of NaCl can be represented as follows: NaCl(s)Na+(aq)+Cl-(aq) The dissociation of Al2(SO4)3 can b e represented as follows: Al2(SO4)3(s)2Al3+(aq)+3SO42-(aq)

Net Ionic Equation

What is a net ionic equation? A net ionic equation includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution.

Writing a net equation First convert the chemical equation into an overall ionic equation. All soluble ionic compounds are shown as dissociated ions in solution. The precipitates are shown as solids. Ions that do not take part in a chemical reaction and are found in solution both before and after the reaction are spectator ions.

Complete Ionic Equation General Equation Cd(NO3)2(aq) + (NH4)2S(aq)  CdS(s) + 2NH4NO3(aq) Complete Ionic Equation Cd2+(aq) + 2NO3-(aq) + 2NH4+(aq) + S2-(aq)  CdS(s) + 2NO3-(aq) + 2NH4+(aq) Net Ionic Equation Cd2+(aq) + S2-(aq)  CdS(s)

Electrolytes By: Pariis Yi, Chase Young, Joey Wofford, Parker Meek, Jonathan Binkley

Electrolytes: A general overview Electrolyte: substance that dissolves in water to give a solution that conducts an electric current A mole of an electrolyte dissolves to make two moles in the solution Non-electrolyte: the substance that does not yield ions and does not conduct an electric current in solution

Colligative Properties Electrolyte is an ionic compound Non-ionic compounds cannot form electrolytes Depends on number of parts

Strong Electrolytes Strong Electrolyte: any compound whose dilute aqueous solutions conduct electricity well There is a presence of all or almost all of the dissolved compound in the form of ions There is a higher concentration of ions

Example NaCl(s) = Na+(aq) + Cl-(aq)

Weak Electrolytes Weak Electrolytes: any compound whose dilute aqueous solutions conduct electricity poorly There is a presence of a smaller amount of the dissolved compound in the form of ions There is a lower concentration of ions

Example H2CO3(aq) = H+(aq) + HCO3-(aq)

Freezing Point Depression Abby Brazinski & Natasha Zelenka

The molal freezing point constant for water is -1.86°C/m. The freezing point of a 1m solution of any nonelectrolyte solute in water is 1.86°C lower than the freezing point of water. The molal freezing point constant for water is -1.86°C/m. The molal freezing point constant is the freezing-point depression of the solvent in a 1-molal solution of a nonvolatile nonelectrolyte solution. Each solvent has its own freezing point constant.

Freezing Point Depression Freezing-point depression, Δtf , is the difference between the freezing points of the pure solvent and a solution of a nonelectrolyte in that solvent, and it is directly proportional to the molal concentration of the solution.

Equation Equation: Δtf = Kfm Kf is expressed as °C/m m is mol solute/kg solvent (molality) Δtf is expressed as the freezing-point depression and is expressed in °C See page 449 in the textbook for an example.

Allison Johnson David Holland, Jr. Osmic Pressure Allison Johnson David Holland, Jr.

Definitions: Osmic Pressure is the external pressure that must be applied to stop osmosis Osmosis – movement of a solvent through a semi permeable membrane* from the side of higher concentration to lower concentration *Semi permeable membrane – allows some particles to pass through while preventing others.

Other facts: Is dependent on concentration of particles, not the type of particles in the solutions Greater the concentration of a solution, the greater the osmic pressure

Example: On one side of the semi permeable membrane is a solution (salt water) and on the other would be the pure solvent (water). Because of the presence of the NaCl molecules in the solution, the solvent is blocked and fewer water molecules are able to reach the membrane and pass through than on the side with pure water…

Example: The pure water passes through the membrane faster and raises the volume of the solution until the pressure exerted by the height of the solution is enough to force the water molecules in the solution back through the membrane at the same rate the water passes through on the other side.

Vapor Pressure Lowering Kaitlynn Motley Artaza Khan Ishaan Sandhu

Vapor Pressure -- The pressure caused by molecules in the gas phase that are in equilibrium with the liquid phase

Colligative Properties -- Properties that depend on the concentration of solute particles but not on their identity Unit: molality (m)

Nonvolatile Substances -- Substance that has little tendency to become a gas under existing conditions Raises boiling point Lowers freezing point When solute in solution, has lower vapor pressure than vapor pressure of pure solvent Vapor pressure of solution = less than pure water

Properties Nonelectrolyte solutions w/ same molality have same particle concentration Equally dilute molal solutions of any type of nonelectrolyte solvent in any solution lower vapor pressure equally Lowering depends on concentration of nonelectrolyte solute Independent of solute identity Colligative property

example Vapor pressure of water over pure water greater than vapor pressure of water over an aqueous solution containing a nonvolatile solute

Boiling-Point Elevation Taylor Walsh Justin Corr Brendan Korando

The cool slide A change in vapor pressure of a liquid will cause a change in the boiling point. The boiling point of a solution is higher then boiling point of a solvent.

Molal Boiling-Point Constant Kb The boiling point elevation of a solvent in a 1-Molal solution of a nonvolatile, nonelectrolyte solute. The Molal Boiling point constant for water is .51 degrees Celsius/m

Boiling Point Elevation The difference between the boiling points of the pure solvent and a nonelectrolyte solution of that solvent, and it is directly proportional to the molal concentration of the solution. Δtb = Kbm Kb = degrees Celsius/m Δtb = The boiling Point Elevation

EXAMPLE