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Chemistry SM-1232 Week 6 Lesson 2

Chemistry SM-1232 Week 6 Lesson 2. Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 2008. Class Today. Take Home Quiz Friday No class on Friday Review: Solution Concentration, mass percent, Molarity,

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Chemistry SM-1232 Week 6 Lesson 2

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  1. Chemistry SM-1232Week 6 Lesson 2 Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Fall 2008

  2. Class Today • Take Home Quiz Friday • No class on Friday • Review: Solution Concentration, mass percent, Molarity, • Wednesday- stoich, Freezing point depression, boiling point elevation • Friday: Take home quiz will be posted on the wiki under week six • Monday- Chapter 14, HW due • Wednesday- WE DO HAVE CLASS • Friday- On Break

  3. Mass Percent • Mass is similar to how much it weighs • Percent: How much per 100 units. • In this case, how much of the mass comes from 1 part of the total mass?

  4. Mass Percent Mass of Solute X 100 = mass percent Mass of Solution Quick percent trick: Percent always means divide the little number by the big number and multiply by 100.

  5. MOLARITY!!! • This is a huge topic!!! A ton of chemistry is done in solutions!!! THIS IS HOW WE UNDERSTAND IT!!! • YOU MUST REMEMBER WHAT IS ON THE NEXT SLIDE!!!

  6. Molarity • Molarity = M • M = moles solute/ L of solution • THIS IS A CONVERSION FACTOR BETWEEN LITERS OF SOLUTION AND MOLES!!!!!!!!!!!!

  7. Ion Conentration • Remember how I showed you how ions dissolve in water? What you saw was NaCl dissolving. • For each molecule of NaCl that dissolves how many Na atoms go into the water? How many Cl atoms go into the wateR? • Would the same be true of CaCl2? How many Ca atoms go into solution for 1 molecule of CaCl2? Cl atoms?

  8. Ion Concentration Calcs • You have a 2.8M solution of AlCl3. In 1 L of solution how many moles of Al atoms are in solution? How about Cl atoms? • If you have 275mL of solution how many moles of Al are in the solution? How many moles of Cl are in the solution?

  9. Solution Dillution • M1V1=M2V2 • This is the equation to use to figure out what happens to the number of moles as we change the volume.

  10. New Material: Freezing Point Depression • Salt lowers the melting point of ice. • Salty icewater baths are below 0C. • To figure out how much the depresion will be we’ll need to use Molality (m)

  11. Molality • Molality (m) = Moles Solute/ kg Solvent.

  12. Molality • Calculate the molality of a solution containing 44g of ethanol (C2H6O) in 300mL of water.

  13. Freezing Point Depression • The change in temperature = Molality x the freezing point depression constant • DTf= m x Kf • Kf of water = 1.86 Ckgsolvent/mol solute

  14. Example • Calculate the freezing point depression of a 2.3 m ethylene glycol solution.

  15. Boiling point elevation • DTb= m x Kb • Kb water = 0.512 Ckgsolvent/mol solute • Calculate the boiling point of a 3.4 m solution of ethylene glycol

  16. Mole Map • We’re going to create a mole map in class. It will look like a tournament bracket of sorts. On the left you’ll have grams, volume of gas at stp, Liters of solution (and molarity), and atoms (and molecules). Those will focus down to 1 place which will have moles A as the units. It will then go to Moles B. Then you’ll expand back out to grams, volume of a gas at stp (molarity), liters of solution, and atoms (molecules). Above each line you’ll write what to multiply by to change from one unit into another.

  17. Practice Stoich • Use the following reaction. Sodium carbonate (Na2CO3) and water decompose into NaOH and Carbon Dioxide. • Convert the following: • 325g Na2CO3 into L of CO2 • 2L of a 2.5M solution Na2CO3 into grams NaOH • 55.43L of CO2 into moles Na2CO3 • 5g Na2CO3 into a 5L solution of X Molar NaOH • 3 Moles of NaOH into moles of CO2 • 69.4g Na2CO3 into molecules and atoms of O2 and O

  18. To Do • Be ready for your quiz on Friday!!! Due Monday.

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