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

I. Do nowII. Percent Composition by Mass:

examples and practice problemsIII. Empirical vs. Molecular FormulasIV. Pre-lab and using a Bunsen burnerHomework: Week 11 Homework #1-8Read lab handout carefully!

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)?

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)

Steps

1. Calculate the molar mass of the compound.

2. Calculate the percent composition by mass of the element in the problem, but keep it as a decimal, not a percent!

3. Multiply the percent composition of that element x the mass given in the problem.

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!)

Agenda

I. Do nowII. Homework answersIII. Empirical vs. Molecular FormulasIV. Calculating a Molecular FormulaV. Pre-lab and using a Bunsen burnerHomework: Week 11 Homework #6-8

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?

Agenda

I. Do nowII. Homework solutionsIII. Determining molecular formulasIV. Determining formulas given

empirical dataHomework: Week 11 Homework #6-

12: Fri.

Empirical and Molecular Formulas

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

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

What is the empirical formula for each of the following?

1. H2O2

2. C6H6

3. CH4

4. C2H10

5. C12H22O11

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

Examples

Ex 2: CH with a molar mass of 39 g/mol.

Ex 3: CH2O with a molar mass of 240 g/mol

Determine the molecular formula

1. CH4N with molar mass 60 g/mol

2. CH2O with molar mass 150 g/mol

3. HgCl with molar mass 472 g/mol

Which have the same empirical and molecular formulas?

C2H4O2 and C6H12O6

NaCrO4 and NaCr2O7

Which is both an empirical and a molecular formula?

C5H10O5 (ribose) C6H12O2 (ethyl butyrate) C55H72MgN4O5 (chlorophyll) C12H17ON (DEET)

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?a. C2H4O2 and C6H12O6

b. NaCrO4 and NaCr2O7

Agenda

I. Do nowII. Pre-lab discussion, safety and using

a Bunsen burnerIII. Lab!IV. Lab calculations and conclusionsHomework: Complete lab packet (#5

is optional): Mon.Advance notice: Test Weds.

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

Lab – water of hydration

Anhydrous – The form of a hydrate-forming compound with NO water in its structure

Salt – Any ionic compound

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) heat

Using a Bunsen burner

1. Be sure the gas valves at your station are turned off.

2. 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.

3. Open the gas valve at your station. You should hear a soft hissing sound.

4. Immediately, hold the flint lighter above, and at an angle to, the top of your Bunsen burner. Squeeze to produce a spark.

Using a Bunsen burner

5. 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.

6. 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.

7. To extinguish the flame, turn off the gas at your station.

8. NEVER leave the Bunsen burner lit unless you are actively using it!

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!!

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.

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.

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?

Agenda

I. Do nowII. Homework solutionsIII. Empirical formula practice

problemsIV. Lab report writing overviewV. Lab report work timeHomework: Finish Week 11

Homework, Lab report 1st draft due Friday, Dec. 3

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

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

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

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.

Practice Problems

1. Calculate the empirical formula of a compound composed of 79.8% C and 20.2% H

2. Calculate the empirical formula of a compound composed of 67.6% Hg, 10.8% S and 21.6% O.

3. 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.

4. Calculate the molecular formula of the compound in #3 if the molar mass is 204 g/mol.

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

Homework!

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

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:a. Divide all numbers by the smallest number of

moles.b. Change % to gramsc. Round to the nearest whole number and use

that number as the subscriptd. Divide by atomic mass to get moles

Agenda

I. Do nowII. Homework solutionsIII. Lab report rubricIV. “Determine the formula” self-assessmentV. Practice ProblemsVI. Unit Review Game!Test WednesdayHomework: Finish Practice Section III

(Section IV is optional but helpful!)Lab report: Due next Friday

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)

Hand out lab report rubric

Title Your lab report should be titled with a title of your

choosing. It should be relevant to the lab and should not just be the

same as the title of a handout your teacher gave you. Do not have it on a separate title page. Include your name, the date, class section and the names

of your lab partners

Background InformationProvide an overview of necessary information

Explain any important concepts that are central to understanding the experiment.

In paragraph form, define any scientific terms necessary for understanding the lab.

Link these concepts and terms together into a coherent paragraph

Objective State the reasons for the experiment

Explain what the purpose of the experiment or what goals you have in completing the lab. What do you hope to accomplish?

Summary of ProcedureSummarize what you did

Write a summary of what you did. Do not rewrite the given procedure word for word. The summary should be in paragraph form and, ideally, in past tense.

Include a labeled diagram of the experimental set-up.

Data and ResultsPresent the results of your experiment.

Include a data table that shows what data you collected. Be sure it shows what each number means!

Data should be presented neatly! Include all calculations you did. Show each step

and a short description of what you did for each step.

Include paragraph(s) of qualitative data and descriptions.

AnalysisDiscuss patterns and trends in the data

Describe what your data mean. That is, what do the results of your calculations tell you?

Describe what your qualitative observations mean.

ConclusionsExplain what you can draw from the data

Was the experiment successful at completing the objectives above? Explain why or why not.

Calculate the actual percent water by mass of CuSO4·5H2O.

Compare your percent water to the actual percent water by calculating percent error. Show your calculations.

Describe all sources of error in the experiment. Explain how they affected your data (for example, did they make your mass of water increase or decrease? Did this make your moles of water increase or decrease? Did this make your number of molecules of water increase or decrease? Be specific!)

Explain how each of your errors could be minimized and improved.

Self-Assessment

1. Silently, on your own, solve the first three problems (Type A, B and C) and check your answers. (12 min.)

2. 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.

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

Homework

Test WednesdayFinish Practice Problems Section III: due

tomorrowSection 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

24 Nov. 2010

Objective: SWBAT show what you know about moles conversions and determining formulas on a test!!

Questions?

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!)

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.