March 25th, 2010

Here are the R values for everyone--

• Justin and Griff--0.07563
• Joe and Ben-- 0.07718
• Taylor and Nick-- 0.0727
• Henry and Evan-- 0.06379
• Matt Orians and Kyle-- 0.06697
• Charlie and Chris-- 0.0814
• Ryan and Jim-- 0.07667
• Donnie and Colby-- 0.07833
• Alex and Jacob-- 0.06356
• Will Long and Matt Johnson-- 0.07997
• Riley and Patrick Blose-- 0.07383
• Matt Farrel and Andrew Parmenter-- 0.06745
• Patrick "The Sweenenator" Sweeney and Peter-- 0.07885

Notes:

• The effect of temperature on the solubility of solids in liquids is more difficult to predict
• increasing the temperature increases the solubility of solids
• equivalent temperature increase can result in a large increase in solubility for some solvents and only a slight change for others
• in some cases, solubility of a solid decreases with an increase in temperature
• the formation of a solution is accompanied by an energy change.
• if you dissolve some KI in water you will find that the outside of the container feels cold to the touch
• if you dissolve some NaOH in water, the outside of the container feels hot
• the formation of a solid-liquid solution can apparently either absorb or release energy as heat
• before dissolving begins, solvent molecules are held together by intermolecular forces.
• in the solute, molecules are held together by intermolecular forces
• energy is required to separate solute molecules and solvent molecules from their neighbors
• a solute particle that is surrounded by solvent molecules is said to solvated
• the net amount of energy absorbed as eat by the solution when a specific amount of solute dissolves in a solvent is the enthalpy of solution
• the enthalpy of solution is negative (energy released) when the sum of attractions from Steps 1 and 2 is less than Step 3
• the enthalpy of solution is positive (energy absorbed) when the sum of attractions from steps 1 and 2 is less than Step 3
• the concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution
• "dilute" just means that there is a relatively small amount of solute in a solvent
• note that these terms are unrelated to the degree to which a solution is saturated. a saturated solution of a substance that is not very soluble might be very dilute
• Molarity is the number of moles per solute in one liter of a solution
• to relate the molarity of a solution to the mass of solute present, you must know the molar mass of the solute. for example, a "one molar" solution of NaOH contains one mole of NaOH in every liter of solution
• the symbol for molarity is M, and the concentration of one molar solution of sodium hydroxide is written as 1 M NaOH
• one mole of NaOH has a mass of 40.0 g. If this quantity of NaOH is dissolved in enough water to make exactly 1.00 L of solution, the solution is a 1 M solution

molarity (M) = amount of solute (mol)/volume of solution (L)

• note that a 1 M solution is not made by adding 1 mol of solute to 1 L of solvent. in such a case, the final total volume of the solution might not be 1 L.
• the resulting solution is carefully diluted with more solvent to bring the total volume to 1 L
• see pages 420 and 421 for the answers and explanations of Sample Problems A, B, and C
• the lab is due tomorrow. dont forget to find the class avg and % error of the class average, as well as writing your conclusion