Solubility and Concentration

Part I Solubility: The ability of a solute to dissolve in a solvent. Expressed as g solute/100g H2O or g solute/100mL H2O

Soluble • Soluble: a solute that has appreciable solubility.

Miscible Substances that dissolve in each other.

Solubility Curves

Precipitate: solute that comes out of solution. •

Types of Solutions Saturated contains the maximum amount of solute that can be dissolved at the given conditions of T and P. Unsaturated contains less than the saturated amount of solute. Supersaturated contains more than the saturated amount of solute by dissolving at higher temp and then cooling.

A supersaturated solution crystallizes after a seed crystal is introduced. http://www.chem.ufl.edu/~itl/2045/change/C12F11.GIF

Rates of Solution Does every candy you eat take the same time to dissolve?

Factors affecting the rate of dissolving: Surface Area Stirring Temperature (average kinetic energy)

Factors Affecting Solubility Temperature (affects solid, liquid and gaseous solutes) Pressure (affects gaseous solutes)

Effect of temperature on solubility of gases. Example: Compare the amount of oxygen dissolved in the waters of the arctic ocean to the amount of oxygen dissolved in warm tropical waters.

Effect of temperature on solubility of solids. Example: Can you dissolve more sugar in warm water or in cold water?

Solubility Curves

Effect of Pressure on solubility of solids. Negligible.

Effect of Pressure on solubility of gases. Henry’s Law: the amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution. The higher the pressure the higher the solubility of the gas.

Effect of Pressure on solubility of gases. http://www.chem.ufl.edu/~itl/2045/lectures/lec_i.html

Example An unopened bottle of soda has a pressure of 5atm above the liquid, so the concentration of CO2 in the soda is high. Compare that to a pressure of 1 atm above the liquid when the bottle has been opened.

Part II Concentration: A measure of the amount of solute dissolved in the solution. Molarity (M) Molality (m) Mole Fraction (x) Percent by Mass (%)

Part II Concentration

Molarity Moles of Solute Molarity (M) = Liters of Solution • A unit of concentration of a solution expressed in moles solute per liter of solution. (Note: 1L = 1 dm3) Moles of Solute Molarity (M) = Liters of Solution

Why Molarity ? http://www.chem.ucla.edu/~gchemlab/volumetric_soln_conc.jpg

Steps involved in the preparation of a standard aqueous solution

Process of making 500 mL of a 1.00 M acetic acid solution

Ex. 1 Molarity What is the molarity of a solution of 8g NaOH in 100mL of solution? Answer: 2M NaOH

Ex. 2 Molarity How many grams of NaOH are contained in 2L of a 3M NaOH solution? Answer: 240g NaOH

Making Dilutions Moles Solute=M1V1=M2V2 M molarity V volume

Ex. 3 Dilutions How many milliliters of 2.00M MgSO4 solution must be diluted with water to prepare 100.00 mL of 0.400M MgSO4? Answer: 20.0mL

Percent by Mass % by mass= Mass of solute x 100 % Mass of solution

Percent by Volume % by volume= Volume of solute x 100 % Volume of solution

Part III Molality and Mole Fraction

Molality (m) = moles solute kg solvent Moles of Solute per kilogram of Solvent Molality (m) = moles solute kg solvent

Mole Fraction xsolvent = Moles of solvent Moles of solution xsolute = Moles of solute Moles of solution xsolvent = Moles of solvent Moles of solution xsolute + xsolvent= 1