1 / 50

A: 16 Nov. 2010

A: 16 Nov. 2010. Objective: SWBAT calculate percent composition for a compound and determine the percentage of water in a hydrate using laboratory techniques Do now : Calculate the molar mass of calcium chloride. (Hint: Write the correct formula first!). Agenda. Do now

arcelia
Download Presentation

A: 16 Nov. 2010

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A: 16 Nov. 2010 • Objective: SWBAT calculate percent composition for a compound and determine the percentage of water in a hydrate using laboratory techniques • Do now: Calculate the molar mass of calcium chloride. (Hint: Write the correct formula first!)

  2. Agenda • Do now • Percent Composition by Mass: examples and practice problems • Empirical vs. Molecular Formulas • Pre-lab and using a Bunsen burner Homework: Week 11 Homework #1-8 Read lab handout carefully!

  3. Percent Composition by Mass • What is the percent composition of each element in dinitrogen trioxide? • What is the percent composition of each element in magnesium nitrate? • What is the percent composition of each element in glucose (C6H12O6)?

  4. a tougher problem… • Calculate the number of grams of nitrogen in 50.0 grams of dinitrogen trioxide. • Calculate the number of grams of magnesium in 10.0 grams of magnesium nitrate • Calculate the mass of carbon in 82.0 g of glucose (C6H12O6)

  5. Steps • Calculate the molar mass of the compound. • Calculate the percent composition by mass of the element in the problem, but keep it as a decimal, not a percent! • Multiply the percent composition of that element x the mass given in the problem.

  6. C: 17 Nov. 2010 • Take Out Homework: Week 11 #1-5 • Objective: SWBAT differentiate between empirical and molecular formulas and calculate a molecular formula. • Do now: (in your notebook) Calculate the percent composition by mass of each element in silver sulfide. (Hint: Write the correct formula first!)

  7. Agenda • Do now • Homework answers • Empirical vs. Molecular Formulas • Calculating a Molecular Formula • Pre-lab and using a Bunsen burner Homework: Week 11 Homework #6-8

  8. A: 18 Nov. 2010 • Take out homework: Week 11 #1-5 • Objective: SWBAT to write empirical and molecular formulas for a compounds, given laboratory data • Do now: What is the empirical formula of the compound C8H4O12?

  9. Agenda • Do now • Homework solutions • Determining molecular formulas • Determining formulas given empirical data Homework: Week 11 Homework #6-12: Fri.

  10. Empirical and Molecular Formulas

  11. Molecular Formula • Gives a complete list of all the atoms in a molecule • Ex: H2O • 2 atoms of H, 1 of O • Ex: C6H12O6 • 6 atoms of c, 12 of H, 6 of O

  12. Empirical Formula • Just gives the lowest, whole number RATIO of elements in the compound • empirical: “by experiment” • Ex: Glucose(Molecular formula: C6H12O6) • Empirical Formula: CH2O • (what is the multiplier?) • Ex: Water(Molecular formula: H2O) • Empirical Formula: H2O

  13. What is the empirical formula for each of the following? • H2O2 • C6H6 • CH4 • C2H10 • C12H22O11

  14. Finding Molecular formula • Ex 1. What is the molecular formula for a compound with the empirical formula HO and a molar mass of 36 g/mol? • STEP 1 – find the total mass of the empirical formula given to you • STEP 2 – divide the molar mass from the problem by the mass of the empirical formula • STEP 3 – multiply each subscript in the emp. form by the number you just found

  15. Examples • Ex 2: CH with a molar mass of 39 g/mol. • Ex 3: CH2O with a molar mass of 240 g/mol

  16. Determine the molecular formula • CH4N with molar mass 60 g/mol • CH2O with molar mass 150 g/mol • HgCl with molar mass 472 g/mol

  17. Which have the same empirical and molecular formulas? • C2H4O2 and C6H12O6 • NaCrO4 and NaCr2O7

  18. Which is both an empirical and a molecular formula? • C5H10O5 (ribose) • C6H12O2 (ethyl butyrate) • C55H72MgN4O5 (chlorophyll) • C12H17ON (DEET)

  19. C: 19 Nov. 2010 • Take Out: % Water in a Hydrate Lab Handout • Objective: SWBAT calculate the percent water in a hydrate and determine the hydrate’s molecular formula. • Do now: Which pair of formulas have the same empirical formula? What is it? • C2H4O2 and C6H12O6 • NaCrO4 and NaCr2O7

  20. Agenda • Do now • Pre-lab discussion, safety and using a Bunsen burner • Lab! • Lab calculations and conclusions Homework: Complete lab packet (#5 is optional): Mon. Advance notice: Test Weds.

  21. Lab – water of hydration • Hydrate – An ionic compound that contains water molecules as part of its crystal structure • Naming/writing formulas • CaCl2 •2H2O – Calcium Chloride dihydrate • This is a compound where each molecule of calcium chloride is combined with 2 molecules of water in the crystal structure • The prefixes are the same as for naming compounds

  22. Lab – water of hydration • Anhydrous – The form of a hydrate-forming compound with NO water in its structure • Salt – Any ionic compound

  23. Lab – water of hydration • Objective: To determine the percentage of water in a hydrate, and to calculate the ratio of the number of moles of water to the number of moles of anhydrous salt molecules. • You will be removing the water from a hydrate and calculating how much water was in it and then using that value to calculate the formula for the compound • CuSO4·XH2O(s) CuSO4(s) + H2O(g)

  24. Using a Bunsen burner • Be sure the gas valves at your station are turned off. • Attach the black tubing to the gas outlet at your station and attach the other end to your Bunsen burner. Be sure the tubing is attached securely. • Open the gas valve at your station. You should hear a soft hissing sound. • Immediately, hold the flint lighter above, and at an angle to, the top of your Bunsen burner. Squeeze to produce a spark.

  25. Using a Bunsen burner • If the flame is not immediately ignited, turn off the gas at your station and wait several minutes until the gas has dissipated before trying again. • Once lit, turn down the gas at the station, and then use the airflow adjustments on the Bunsen burner to produce a quiet flame with smooth edges and two distinct cones: a darker blue cone inside a lighter blue cone. • To extinguish the flame, turn off the gas at your station. • NEVER leave the Bunsen burner lit unless you are actively using it!

  26. Lab – % Water in a Hydrate • Never set a hot object directly on the lab bench: place it on a wire mesh. • Never place a hot object on a balance. Let it cool to the touch first. • Heat with the cover OFF, cool with the cover ON. • Be careful not to burn your substance. Stir and move the crucible in and out of the flame to evaporate evenly. • A hot crucible and a cool crucible look the same!!

  27. Goggles stay on for the entire lab, until your area is completely clean. • When you finish the lab, clean up your area completely. • Return clean, dry equipment to the front table. • Then, sit down with your group and begin calculations.

  28. Homework • Lab worksheet due Monday with all completed calculations. Show all work! (#5 optional) • Test Weds. • You will be writing a formal lab report – started in class next week.

  29. A: 19 Nov. 2010 • Take Out Homework: Week 11 #6-10 and Hydrates Lab worksheet! • Objective: SWBAT calculate an empirical formula from lab data, and write a lab report for the hydrate lab. • Do now: What is the molecular formula for the compound with empirical formula PCl2 and molar mass 306 g/mol?

  30. Agenda • Do now • Homework solutions • Empirical formula practice problems • Lab report writing overview • Lab report work time Homework: Finish Week 11 Homework, Lab report 1st draft due Friday, Dec. 3

  31. Finding Empirical Formula in the Lab • When we do Analytical Chemistry in the lab, we can find values for the amount of a certain element in a compound • Like when we found the amount of water in CuSO4 • XH2O • We have a system for taking the values we get in the lab and figuring out the empirical formula

  32. Determine the empirical formula for a compound that is 74.83% carbon and 25.17% hydrogen by mass STEP 1 - Pretend you have 100 grams of the substance, make the % values into numbers of grams STEP 2 - Convert each mass value into moles STEP 3 - Divide all mole values by smallest # of moles STEP 4 - Use the resulting numbers as your subscripts

  33. Determine the empirical formula for a compound that is 25.9% nitrogen and 74.1% oxygen. STEP 1 - Pretend you have 100 grams of the substance, make the % values into numbers of grams STEP 2 - Convert each mass value into moles STEP 3 - Divide all mole values by smallest # of moles STEP 4 - Use the resulting numbers as your subscripts

  34. Finding Empirical Formula • Sometimes you won’t be given percentages, but values for each element out of a total value • Ex: What is the empirical formula for a compound where a 10.0 g sample contains 9.41 g O and 0.59 g H? • To solve: Just write down the number of grams of each, then proceed as before.

  35. Practice Problems • Calculate the empirical formula of a compound composed of 79.8% C and 20.2% H • Calculate the empirical formula of a compound composed of 67.6% Hg, 10.8% S and 21.6% O. • Calculate the empirical formula of a compound where a 50.0 gram sample contains 29.4 g of C, 4.90 g H and 15.7 g O. • Calculate the molecular formula of the compound in #3 if the molar mass is 204 g/mol.

  36. For the rest of class… • Choose one section • Spent the rest of this period (quietly!) making a rough draft in your notebook • I’ll pass back papers

  37. Homework! • Week 11 HW, # 11 – 15: Fri. • Lab report first draft: Friday. Dec. 3

  38. C: 23 Nov. 2010 • Take Out Homework: Week 11 #9-16 • Objective: SWBAT solve all types of “determine the formula” problems. • Do now: Put these steps in order to solve a “calculate the empirical formula” problem: • Divide all numbers by the smallest number of moles. • Change % to grams • Round to the nearest whole number and use that number as the subscript • Divide by atomic mass to get moles

  39. Agenda • Do now • Homework solutions • Lab report rubric • “Determine the formula” self-assessment • Practice Problems • Unit Review Game! Test Wednesday Homework: Finish Practice Section III (Section IV is optional but helpful!) Lab report: Due next Friday

  40. C: This week • Today: Extra help after school!!! 3:30-4:30 Room 203 • Wednesday: Unit Test • Atoms/molecules  moles  mass problems • Determining empirical/molecular formulas • Thursday/Friday: No class!  • Next week Mon: Lab report work time (we just ran out of time this week)

  41. Hand out lab report rubric

  42. Self-Assessment • Silently, on your own, solve the first three problems (Type A, B and C) and check your answers. (12 min.) • Work on Section II: Use the results of Section I to determine which types of problems you need to practice most! • For example, if you got “Type A” wrong in Section I, do Section II, Type A.

  43. After you take the self-assessment… • Parts of Section II are optional, but recommended if you got any of Section I wrong. • You MUST complete Section III – Mixed Practice, and check your answers. • Section IV is optional (but recommended!) – Practice Quiz, and check your answers. • Anything you don’t finish by the end of 1st period is homework

  44. Homework Test Wednesday Finish Practice Problems Section III: due tomorrow Section IV is optional, but a great way to study! Study your mass-moles-atoms/molecules quiz, and redo problems you got wrong Lab report: Due next Friday

  45. 24 Nov. 2010 • Objective: SWBAT show what you know about moles conversions and determining formulas on a test!! • Questions?

  46. Periodic table is on the last page. • You can rip it off! • When you are finished, do one of the following: • Begin working on your lab report first draft in your notebook. • Lab report work day Monday! • Begin working on extra credit problems. (due Monday!)

  47. Lab report work time • Save your work to a USB or to your email, NOT to the desktop or laptop!! • Stay in your seat and work quietly. • Follow the checklist!! • Raise your hand if you have questions. • Lab report due Friday, December 3 in class.

More Related