SOLUTIONS SUROVIEC SPRING 2015 Chapter 12

I. Types of Solution Most chemical reaction take place between ions/molecules dissolved in water or a solvent. Solution: homogenous mixture of 2 or more substances in a single phase

II. Molecular view of solution process Liquids and solids held together by intermolecular attractions Looking at specifically  Solvent-solvent  Solvent - solute  Solute – solute 3 steps  Separate solvent molecules  Separate solute molecules  Mix together

Ex. Dissolve CaCl 2 (s) in H 2 O What happens to the concentration of Ca 2+ and Cl - ? Saturated: stable solution in which the maximum amount of the solute has been dissolved Equilibrium in solution Solubility: concentration of solute in equilibrium with undissolved solute in a saturated solution

Examples: CCl 4 and CH 4 NaCl and CCl 4

III. Concentration A. Molarity: (M) Moles of solute / liter of solution Does not tell us the EXACT amount of volume to use B. Molality: (m) Mole of solute / mass of solvent (kg) Cannot be the same measure of a solution

Example The concentration of a K 2 CrO 4 solution is undetermined, but it was prepared from 38.3 g of K 2 CrO 4 (MW 19.4 g/mol) and 1.00 kg of water. What is the molality? Calculate the molality of 1 L of 1.22M sucrose (MW g/mol) solution. The density of the solution is 1.12 g/mL.

C. Mole Fraction Amount of the component we are interested divided by the total amount of all the components of the mixture Mole fraction of A (X A ) =

example Consider a solution that has 1.00 mole ethanol (46.1 g) dissolved in 9.00 moles of water (162 g). Find the mole fraction of each.

D. Mass Percent Common unit of measurement for consumer products Mass of one component divided by the total mass of the mixture multiplied by 100%

Example Consider an alcohol-water mixture that is prepared by dissolving 46.1 g of ethanol in g of water. What is the mass percent of ethanol in the mixture?

IV. Pressure, Temperature and Solubility A. Solid solubility and Temperature When a solid is dissolved an equilibrium is established An increase in temp will shift the equilibrium

B. Gas Solubility Solubility of gasses decreases with increasing temperature Why do fish go to bottom of lake in the summer? Gases that dissolve to an appreciable extent in water do so in an exothermic process So what do you need to do to get the gas out of the water?

V. Pressure and Solubility A. Henry’s Law Solubility of a gas in a liquid is directly proportional to the gas pressure Henry’s Law c g = k H P g  c g = molar concentration (mol/L)  k H = Henry’s law constant (mol/L · atm)  P g =pressure of a gaseous solute (atm)

Example Deep-sea diving Solubility of gases is the concentration of gases in equilibrium with substances in gaseous state What would happen if we increased the pressure?

VI. Colligative Properties Properties of a solution that depend only in the number of solute particles per solvent molecule and not the nature of the solute or solvent

A. Raoult’s Law Equilibrium vapor pressure: pressure of the vapor when the liquid and the vapor are in equilibrium

Example Solution contains 82.0 g of ethylene glycol in 100g of water at 22 o C. (where is vapor pressure of water is mm Hg) what is the new vapor pressure?

B. Boiling Point Elevation You have a solution of mole of sugar in g of benzene The normal vapor pressure of pure benzene is 400 mmHg, what is the new vapor pressure of this solution?

This vapor pressure lowering causes a BP elevation! Normal BP is the temp at which vapor pressure =760 mm Hg BP elevation

B. BP elevation Leads to general equation: The melting point of water is 0 o C at 1atm. If g of ZnSO 4 (MW g/mol) are dissolved into g of water:  What is the molality of the solution  What is the new melting point of the solution?

C. Freezing Point Depression Freezing point of a solution will be lower than of a pure solvent General equation Why add antifreeze to your car?