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Investigation 10: Stoichiometry

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The Stoichiometry of Filling a Balloon

Performance Assessment

In this lab experience, students will determine the amount of sodium bicarbonate to add to acetic acid to produce a specific amount of CO2 gas. They will use the results to determine which reactant is the limiting reagent and which is in excess. Students will observe that no matter how much sodium bicarbonate is added, at some point it becomes the excess reagent and there is not enough acetic acid to react. As a result there is a limited amount of carbon dioxide gas that can be produced. When smaller amounts of sodium bicarbonate are added, it is the limiting reagent and the acetic acid is the excess. When the moles of sodium bicarbonate exceed the moles of acetic acid, the designations switch and acetic acid becomes the limiting reactant.

Materials Included in Kit

Consumable:
Acetic acid, 2 M, 750 mL
Sodium bicarbonate, 170 g
Balloons, 80
Weigh dishes, 60
Additional Materials Required
Flinn Scientific Electronic Balance, 410 x 0.01-g, 10
Cylinder, Borosilicate Glass, 50 mL, 10
Flask, Erlenmeyer, Borosilicate Glass, 125 mL, 30
Powder Funnel, Polypropylene, 80 mm, 10
Spatulas, Disposable, Box of 300, 1

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Identify Unknowns Through Stoichiometry

In this lab experience, students will investigate the identity of an unknown group 1 metal carbonate through titration. This will give them insight into how scientists can learn the identity of unknown substances. Students should become comfortable with stoichiometry calculations and how that information can be useful in determining the unknown identities of different compounds. Both techniques used in this lab help students understand the importance in being precise and accurate when making measurements. When using the mass loss of carbon dioxide to determine the identity, the outcome is heavily dependent on careful measurements. The mass of CO2 lost is small and can be obscured by poor measurements. With titrations there needs to be care in not overshooting the endpoint, as that can lead to inaccurate calculations that could in turn affect the identification of the unknown metal carbonate.

Materials Included in Kit

Consumable:
Bromocresol green indicator solution, 0.04%, 35 mL
Hydrochloric acid solution, 0.1 M, 1 L
Hydrochloric acid solution, 2 M, 500 mL
Potassium carbonate, 60 g
Sodium carbonate, 60 g
Weighing dishes, 50
Additional Materials Required
Beakers, Borosilicate Glass, 50-mL, 10
Beaker Tongs with protective sleeves, 10
Buret, Borosilicate Glass, with Glass Stopcock, 50-mL, 10
Flinn Scientific Electronic Balance, 300 x 0.1-g, 10
DLAB Classic Magnetic Stirrer/Hot Plate, 10
Single Buret Clamp, Plastic-Coated Jaw, 10
Flask, Erlenmeyer, Borosilicate Glass, 125 mL, 30
Cylinder, Borosilicate Glass, 25 mL, 10
Cylinder, Borosilicate Glass, 50 mL, 10
Cylinder, Borosilicate Glass, 500 mL, 10

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Determination of Reaction Output

In this lab experience, students use stoichiometry calculations to predict the mass of product in a reaction of sodium bicarbonate with heat. This lab really helps students practice stoichiometry calculations and understand the molar relationship between reactants and products. Here they are given a target value of product they must generate. The success of their reaction depends on the accuracy of their math. This challenge of hitting a specific value of product gives students an appreciation for how industrial chemists work toward a quota of material to be produced every day.

Materials Included in Kit

Consumable:
Calcium acetate, 25 g
Calcium chloride, 300 g
Magnesium sulfate, 50 g
Potassium carbonate, 100 g
Sodium bicarbonate, 100 g
Sodium carbonate, 100 g
Universal indicator solution, 20 mL
Zinc sulfate, 25 g
Glass wool, 3 g
Non-Consumable:
Universal indicator charts, 10
Additional Materials Required
Flinn Scientific Electronic Balance, 410 x 0.01-g, 10
Beakers, Borosilicate Glass, 50-mL, 20
Beakers, Borosilicate Glass, 150-mL, 10
Büchner Funnel, Porcelain, 100-mm, 10
Oven, Laboratory, 0.7 Cubic Feet, 10
Stopper for Büchner funnel, no. 6, 10
Filtering Flask, 250-mL, 10
Oven, Laboratory, 2.0 Cubic Feet, 1

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Formation of Barium Iodate

In this lab experience, students vary the amounts of either barium ion or iodate ion to evaluate limiting reagents and how the mole ratio between the reactants plays a role. The importance of stoichiometry calculations is the primary focus of this lab. Students will use different reactant volumes to evaluate limiting and excess reagents. They will see that one single reactant is not always limiting. The molar ratio between the reactants is what determines whether one is limiting and the other is in excess. This lab will also help students understand the difficulty in achieving perfect molar equality between the reactants. There is generally always an excess and limiting reactant. But with careful calculations that excess can be minimized.

Materials Included in Kit

Consumable:
Barium chloride solution, 0.2 M, 1 L
Potassium iodate solution, 0.2 M, 1 L
Sodium bisulfate/starch indicator solution, 200 mL
Sodium sulfate solution, 0.1 M, 125 mL
Syringes, 10 mL, 20
Pipets, 100
Wood splints, package of 100
Non-Consumable:
Test tubes, 16 mm x 100 mm, 50
Additional Materials Required
Reaction Plates, 24 Wells, 10
Ruler, Metric, Clear, 30 cm, 10
Test Tube Rack, Economy Choice, 10

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Build a Film Canister Rocket

Engineering Design Challenge

In this lab experience, students design a film canister rocket that will fly at least one meter into the air using a specific ratio of reactants as fuel. Students will find that the mass difference between the rocket and the baking soda was a key factor in a successful launch. Sodium bicarbonate will be the limiting reactant when the mass is less than one gram since the volume of acetic acid remains constant. Students will also observe that the heavier rockets are slower to launch, but generally the most successful. This lab also helps students understand the importance of stoichiometry calculations because they are given a finite amount of sodium bicarbonate to use for three launches. They must plan carefully so they do not use up their allotment too quickly.

Materials Included in Kit

Consumable:
Sodium bicarbonate, 100 g
Vinegar, 500 mL
Manila folders, 10
Paper clips, box of 100
Tissue (lens) paper, box
Weighing dishes, 20
Non-Consumable:
Film canisters with caps, 15
Additional Materials Required
Demonstration Tray, Large, 10
Flinn Scientific Electronic Balance, 300 x 0.1-g, 10
Meter Stick, Plastic, 10
Spatulas, Disposable, Box of 300, 1
Student Timer, 12-pack, 1