10 January 2011

Take Out Homework: Week 17 p. 3Objective: SWBAT define and identify

the limiting reagent in a chemical reaction.

Do Now: Which type of reaction?a. AX + BY BX + AYb. 2HgO(s) 2Hg(l) + O2(g)

Agenda

I. Do now, homework checkII. Review types of reactionsIII. Limiting reagent demonstration/mini labHomework: Week 18 Homework pages 1-2:

Tues

Limiting Reagent Lab: Due Weds.Quiz on Types of Reactions tomorrow (includes one mass to mass conversion

problem!) (10 min)

Limiting Reagents

Demonstration

Solid sodium bicarbonate reacts with a solution of acetic acid to produce…

You will be working with your lab group to carry out one trial of this experiment.

Listen carefully to the verbal directions! When you finish your trial, bring your flask

+ balloon to the front (don’t take the balloon off the flask!)

Then, finish page 1 and page 2 of the lab handout

Group Amt of baking soda

Amt of vinegar

Circumference of balloon (cm)

Any baking soda left over?

1a 2g 50ml(2.5g)

28.5cm Nah

1b 2g 50ml(2.5g)

31.0 NO

2a 4g 50ml(2.5g)

36.0cm no

2b 4g 50ml(2.5g)

36.1cm no

3a 6g 50ml(2.5g)

36.0cm YES

3b 6g 50ml(2.5g)

36.0 YESSSSSSSSSSSSSSSSSSSS

For the rest of the period…

Complete the lab packet with your group.

Ask me questions if you have them!

If you finish early (wow!) begin the homework (Week 18 pages 1-2)

Homework

Week 18 Homework pages 1-2: tomorrow

Limiting Reagent Lab: Due Weds.Quiz on Types of Reactions tomorrow (includes one mass to mass

conversion problem!) (10 min)

Extra Help TOMORROW 3:30-4:30 pm

NaHCO3(s) + CH3COOH(aq) CO2(g) + H2O(l) +

NaCO3(aq)

14 January 2011

Take Out Homework:Limiting Reagents Lab

Objective: SWBAT determine the limiting reagent in a chemical reaction word problem.

Do now: For our limiting reagents lab, describe how we could have checked to see if there was excess vinegar in flask 1.

Agenda

I. Do nowII. Homework checkIII. Determining the limiting reagentIV. Practice ProblemsHomework:Week 18 Homework p. 1-3: Tuesday

For one sandwich:1 roll 1 slice 2 slices 1 leaf 2 slicesYou have2 rolls 5 slices 6 slices 4 leaves 8 slices

What is the limiting ingredient?Which ingredients are in excess?

Vocab

Limiting reagent: the reactant that limits or determines the maximum amount of product that can be formed in a reaction.

Excess reagent: reactant that is not completely reacted; extra

Ex. 12Na(s) + Cl2(g) 2NaCl(s)

If 6.70 moles of sodium is reacted with 3.20 moles of chlorine gas…a. What is the limiting reagent?b. How many moles of NaCl are produced?

Ex. 1C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g)

If 2.70 moles of C2H4 (ethylene) is reacted with 6.30 moles of oxygen gas…a. What is the limiting reagent?b. How many moles of water are produced?

Complete the front page of the handout.

Practice Problems

Front: Moles problems Back: Mass problems

Bonus! If you finish early, complete part c on the front and back. Due Tues.

Practice Problems! (Part 1)C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g)

1. If 15.0 moles of ethene is reacted with 10.0 moles of oxygen…

2. If 0.50 moles of ethene are reacted with 0.25 moles of oxygen…

a. What is the limiting reagent?b. How much water is produced?**c. How much of the excess reagent is left?**

Homework

Week 18 Homework p. 1-3: Tues.

Missing Work? Still can’t write and balance an equation? Think mass conversions are impossible? Extra Help Tuesday 3:30-4:30

A: 18 Jan. 2011

Take Out Homework: Week 18 p. 3 Objective: SWBAT determine the

limiting reagent in grams in a chemical reaction word problem.

Do now: 2H2(g) + O2(g) 2H2O(l)

a. If 10 moles of H2 are reacted with 4 moles of O2, which is the limiting reagent?

b. How many moles of water can be made?

Agenda

I. Do now, Homework checkII. LR examples with gramsIII. Practice ProblemsHomework: Week 18 Homework p. 4:

Weds.Finish Limiting Reagents worksheet:

Weds.

Ex. 12Na(s) + Cl2(g) 2NaCl(s)

If 2.0 grams of sodium is reacted with 3.0 grams of chlorine…a. What is the limiting reagent?b. How many grams of NaCl are produced?

Ex. 2C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g)

If 5.00 grams of ethylene is reacted with 1.00 gram of oxygen gas…a. What is the limiting reagent?b. How many grams of water are produced?**c. How many grams of the excess product are left?**

Complete page 2 of the handout

Practice Problems

Back: Mass problems Due at the end of the class!

Bonus! If you finish early, complete part c on the front and back. Bonus due tomorrow.

Homework

Week 18 Homework p. 4: tomorrow Finish Limiting Reagents

worksheet bonus: tomorrow

A: 19 January 2011

Take Out Homework: Week 18 p. 4and Limiting Reagents Worksheet

Objective: SWBAT calculate percent yield of a product of a reaction.

Do now: 2H2(g) + O2(g) 2H2O(l)

a. If 6 moles of H2 are reacted with 4 moles of O2, which is the limiting reagent?

b. How many moles of water can be made?

Agenda

I. Do nowII. Homework checkIII. % yield notes and examplesIV. Practice problemsV. Bubblegum lab!Homework: Week 18 Homework p. 5-

6, Finish bubblegum lab: Thurs.

C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g)

If you calculate that the reaction of 5.00 grams of ethylene with 3.00 grams of oxygen will yield 2.75 grams of carbon dioxide, should you expect the actual reaction to really yield exactly that much? Why or why not?

Percent Yield

Theoretical yield: maximum amount of product that could be formed given the amounts of reactants.

(Calculated on paper.)Experimental yield: the amount of

product that actually forms during an experiment

(Determined by doing an experiment.)

Percent Yield is usually < 100%

Why?• Reaction not going to completion• Impure reactants• Side Reactions: a product reacts with

a reactant• Loss during filtration or pouring

between containers

Ex. 1CaCO3(s) → CaO(s) + CO2(g)

You calculate that, with the masses of reactants used, your experiment should have yielded 3.00 grams of solid calcium oxide. However, you only got 2.00 grams of calcium oxide. Calculate the percent yield.

Ex. 2CaCO3(s) → CaO(s) + CO2(g)

a. What is the theoretical yield of CaO if 24.8 grams of CaCO3 is heated?

b. What is the percent yield if 13.1 g CaO is actually produced?

Ex. 3Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

When 84.8 g of iron (III) oxide reacts with an excess of carbon monoxide, 54.3 g of iron is produced. What is the percent yield?

Practice Problems!Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)

1. You calculate that your reaction should have produced 10.0 g of iron, but only 6.8 grams were produced. What is the percent yield?

2. When 10.0 g of iron (III) oxide reacts with an excess of carbon monoxide in an experiment, only 6.45 g of iron is actually produced. What is the percent yield?

3. When 5.00 g of iron (III) oxide is reacted with 1.00 g carbon monoxide, 1.20 grams of iron is produced. What is the percent yield? (Hint: Calculate the limiting reagent FIRST!)

Bubblegum Lab!

What percent of Dubble Bubble is sugar, by mass?

Compared to the Nutrition Facts, what is your percent yield of sugar from Dubble Bubble?

Work with your partner. Choose one “chewer” and one “balancer.”

Homework

Week 18 Homework p. 5-6: Thurs.Finish bubblegum lab: Thurs.

Alka Seltzer

Contains:AspirinCitric acidNaHCO3 (sodium bicarbonate)

How much of Alka Seltzer is actually sodium bicarbonate (NaHCO3)?

P. 3 #1NaHCO3(s) + CH3COOH(aq) CH3COONa(aq) + CO2(g) + H2O(l)

Solid sodium bicarbonate (in the Alka Seltzer) reacts with a solution of acetic acid (in the vinegar) to produce a solution of sodium acetate, carbon dioxide gas, and liquid water.

Using stoichiometry, if we find the mass of the carbon dioxide released, we can calculate the mass of the sodium bicarbonate in the alka seltzer!

And then, the percent by mass of sodium bicarbonate in the alka seltzer!

Determining a Limiting Reagent Lab

Safety: No eating or drinking Used chemicals can be washed down

the sink with water. Do not use lab materials to design

your own lab.

Procedure

You will be reacting different amounts of acetic acid and water with an alka seltzer tablet.

Read directions carefully.Refer to data table 1 on page 2Record qualitative observations.Record data on the back page.

Graphing Experimental Data

Goal: To determine the limiting reagent in the reaction

NaHCO3(s) + CH3COOH(aq) CH3COONa(aq) + CO2(g) + H2O(l)

Graph amount of NaHCO3 vs. amount of CH3COOH

Parts of a Graph

1 2 3 4 5 6 7 8 9

1

2

3

4

5

6

7

8

9

NaHCO3 (g)

CH3COOH (g)

ScaleUnits

ScaleUnits

Title

Plot Points(do not

connect!)

Analysis

What is the trend of the data?Increasing? Decreasing? Constant? Steep slope? Flat slope? Shape (linear, quadratic?)

As (x-value) ______, (y-value) ______.Write one very complete paragraph

describing the trends in your data.

Conclusions

What can you conclude about this experiment based on your graph?

Why do you see the trend in your data?

What is the LR? When? How do you know?

What is in excess? When? How do you know?