Airbag lab baking soda and vinegar answers

CHEMISTRY

Engineering a Better Air Bag Investigation Manual

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ENGINEERING A BETTER AIR BAG

Table of Contents

2 Overview 2 Objectives 3 Time Requirements 3 Background 4 Materials 5 Safety 5 Preparation 6 Activity 1 7 Activity 2 8 Activity 3 10 Disposal and Cleanup

Overview This investigation is a chemical engineering challenge. The task is to investigate a less expensive and less toxic chemical air bag system for the automobile industry. An air bag restraint system will be modeled through a series of steps. First, the quantity in moles of carbon dioxide required to fill a model air bag at room temperature and pressure will be determined using the Ideal Gas Law. Second, the amounts of sodium bicarbonate and acetic acid reactants required to produce a sufficient volume of carbon dioxide to fill the model air bag without bursting it will be calcu- lated. Third, the reaction will be performed to test the inflation of the prototype model air bag with the predicted reactants. The final step involves scale-up and calculation of the reactant quantities required to produce enough carbon dioxide to fill driver-side and passenger-side air bags at room temperature and pressure.

Objectives • Determine the volume of a scale model air bag in liters. • Apply the Ideal Gas Law to calculate the moles of CO2 produced

in a reaction. • Calculate the stoichiometric amounts of reactants required to

produce a specific quantity of product. • Assess reactant amounts by mixing and observing the inflation

of the model air bag.

Key Personal protective equipment (PPE)

goggles gloves apron follow link to video

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stopwatch required

warning corrosion flammable toxic environment health hazard

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Time Requirements Preparation 10 minutes Activity 1: Stoichiometry of

Reactants and Products 20 minutes Activity 2: Testing Model Air Bags 30 minutes Activity 3: Amount of CO2 for Full-

Size Air Bags 10 minutes

Background This lab illustrates how stoichiometry and the Ideal Gas Law can be used to predict the moles of gas needed to fill a model of an automo- bile air bag and how to scale up to predict the number of moles needed to fill full-size air bags.

Stoichiometry is the quantitative study of a chemical reaction and is based upon the coef- ficients of a balanced chemical equation. Coef- ficients represent the molar ratios of reactants to products. These ratios predict the number of moles of reactant needed to produce a given number of moles of product. These molar amounts can be converted into grams for solids or into liters for gases at given temperatures and pressures.

The Ideal Gas Law shows the relationship of all four variables for gases in one equation. That equation is PV = nRT, where P represents pres- sure (in atmospheres [atm]), V represents volume (in liters), n represents the number of moles, R represents the gas law constant (0.0821 L-atm/ mole·K), and T represents temperature (in degrees Kelvin).

Air bags in automobiles activate when an accel- erometer in a microchip senses an impact force equivalent to hitting a wall at a speed of 10–15 miles per hour. The accelerometer closes a switch that ignites a charge, causing a pellet of sodium azide (NaN3) to explode. This explosion releases sodium metal and harmless nitrogen gas that inflate the bag. The reaction is shown in the following equation:

2NaN3(s) ➝ 2Na(s) + 3N2(g)

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ENGINEERING A BETTER AIR BAG

Background continued The sodium metal produced is highly reactive and will react violently with water. Therefore, iron oxide (Fe2O3) is placed in the compartment along with the sodium azide. The sodium metal produced by the inflation reaction in turn reacts with the iron oxide to produce harmless sodium oxide (Na2O) and iron (Fe). Talcum powder or cornstarch is also released during the inflation. These substances keep the air bag pliable and lubricated during storage.

Sodium azide is very toxic. The fate of this compound when it is left in junked cars is a significant environmental concern. Because of sodium azide’s potential to harm the environ- ment, manufacturers are searching for safer, “greener” reactant chemicals for air bag infla- tion. This lab investigates the nontoxic reac- tion of sodium bicarbonate and acetic acid to produce carbon dioxide gas and a harmless salt, sodium acetate.

Materials Included in the materials kit:

6 Resealable plastic bags, 6 × 9 in

Needed from chemical kit 1:

Vinegar, white distilled, 1 pt

Baking soda (sodium bicarbonate), 15 g

Reorder Information: Replacement supplies for the Engineering a Better Air Bag investigation can be ordered from Carolina Biological Supply Company, kit 580308.

Call 800-334-5551 to order.

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Needed from the equipment kit:

Graduated cylinder, 50 mL

Electronic balance

Weighing boat

Plastic spoon

Beaker, 250 mL Thermometer

Safety Wear your safety goggles, chemical apron, and gloves at all times while conducting this investigation.

Read all the instructions for this laboratory activity before beginning. Follow the instructions closely and observe established laboratory safety practices, including the use of appropriate personal protective equipment (PPE) described in the Safety and Procedure sections.

The vinegar and baking soda are not suitable for household consumption or use. They should be considered chemicals and kept away from children and pets.

Do not eat, drink, or chew gum while performing this activity. Wash your hands with soap and water before and after performing the activity. Clean up the work area with soap and water after completing the investigation. Keep pets and children away from lab materials and equip- ment.

Preparation 1. Read the procedure. 2. Obtain all materials. 3. Select a clean work area.

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ACTIVITY

ACTIVITY 1

A Stoichiometry of Reactants and Products

Simulate air bag deployment by mixing reactants to fill a resealable plastic bag with carbon dioxide gas. The goal is to determine the exact stoichiometric amounts of sodium bicarbonate and acetic acid that will react to completely fill a sealed bag without bursting it.

1. The volume of each 6 × 9-inch resealable bag is 1.20 liters.

2. The current air pressure in inches of mercury can be found on local weather reports or by an internet search using the keywords, “air pressure for XXXXX” (where XXXXX is the local zip code).

3. Convert the air pressure from inches of mercury to the nearest 0.01 atmospheres using the following conversion (and record in Data Table 1):

4. Measure the room temperature in °C with a thermometer. Convert to Kelvin by adding 273, and record in Data Table 1 as Kelvin temperature.

5. Use the Ideal Gas Law to calculate the number of moles (n) of carbon dioxide required to fill a 6 × 9-inch bag. Record the number of moles (n) in Data Table 1.

6. Examine the reaction of the weak base, sodium bicarbonate (NaHCO3), and the weak acid found in vinegar, acetic acid (CH3COOH). The products are the aqueous

salt, sodium acetate (CH3COONa), and carbonic acid (H2CO3), an intermediate compound. This quickly breaks down into water and carbon dioxide, as shown in the following equation in bold print:

1. NaHCO3(s) + CH3COOH(aq) ➝ 2. H2CO3(aq) + CH3COONa(aq) ➝ 3. H2O(l) + CO2(g) + CH3COONa(aq)

7. In Data Table 1, write a balanced equation for only the reactants and products in bold print shown above in lines 1 and 3. Line 1 are the reactants and line 3 are the products.

8. Beginning with the moles of carbon dioxide determined in step 5 and the balanced chemical equation, calculate the grams of sodium bicarbonate reactant [MW = 84.0 g/ mol] needed to produce this number of moles of carbon dioxide. Record your results in Data Table 1.

9. The source of acetic acid is a solution of vinegar, which is 0.833 M acetic acid. Beginning with the number of moles of carbon dioxide determined in step 5 and the balanced chemical equation, calculate the volume of vinegar solution required. Record your results in Data Table 1.

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Data Table 1: Model Air Bag

Activity Data and Calculations

Volume of 6 × 9-inch bag 1.2 Liters

Room pressure in atm

Room temperature in Kelvin

Moles of CO2 required to inflate bag at room temperature and pressure

Balanced equation for the reaction of NaHCO3 and CH3COOH to produce CO2

Mass of NaHCO3 needed for the reaction (84.0 g/mol)

Volume of vinegar required (0.833 M acetic acid)

ACTIVITY 2

A Testing Model Air Bags 1. Using the balance and a weigh boat, weigh

the grams of sodium bicarbonate that was calculated in step 8 of Activity 1. Record exact mass in Data Table 2.

2. Using the 50 mL graduated cylinder, measure out the volume of vinegar that was calculated in step 9 of Activity 1.

3. Open a 6 x 9-inch resealable bag and hold it upright with the narrower 6-inch end over the edge of the 250-mL beaker. This should create a peak and two valleys in the bag. See Figure 1.

4. In the valley outside of the beaker, add the sodium bicarbonate powder. After adding the powder, hold the portion of the bag containing the powder tightly against the outside of the beaker. This will help prevent a premature reaction in the next steps.

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ACTIVITY

ACTIVITY 2 continued

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Figure 1.

5. Pour the vinegar into the other valley. Take care not to mix the two reactants before sealing the bag.

6. Carefully remove all the excess air from the bag and seal the bag. The bag must be sealed completely to avoid losing any gas during the reaction.

7. Pick up the bag and tilt it so that the vinegar flows over the sodium bicarbonate and begins to react.

8. Hold the bag by the top seal and shake the bag to mix all the reactants. The reaction should look similar to Figure 2.

9. The reaction is complete when there is only a clear solution left. Leave the bag inflated for comparing to the bags in the next two steps. Record all data and observations in Data Table 2.

10. Repeat the experiment using a fresh, clean bag. Increase the amount of sodium bicarbonate by an additional 0.3 g and the

vinegar by an additional 5 mL. Record exact mass of sodium bicarbonate in Data Table 2. Observe and compare how quickly and how much more the bag inflates.

Figure 2.

11. Repeat the experiment a third time using a fresh, clean bag. Increase the amount of sodium bicarbonate over the original amount by an additional 0.5 g and the vinegar by an additional 10 mL. Record exact mass of sodium bicarbonate in Data Table 2. Observe and compare how quickly and how much more the bag inflates.

ACTIVITY 3 A Amount of CO2 for Full-Size

Air Bags The following activity is intended as an exten- sion activity and requires the application of concepts from the Background and previous activities to solve a mathematical problem.

1. The volume of a driver-side air bag is 80.0 L. Calculate the number of moles of CO2 needed to fill the air bag and the grams of sodium bicarbonate and milliliters of vinegar needed for the reaction. Record all calculations in Data Table 3.

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2. The volume of a passenger-side air bag is 160.0 L. Calculate the number of moles of CO2 needed to inflate the air bag and the

grams of sodium bicarbonate and milliliters of vinegar needed for the reaction. Record all calculations in Data Table 4.

Data Table 2: Model Air Bag

Trial # NaHCO3 (grams)

Vinegar (mL)

Observations

1

2

3

Data Table 3: 80-L Driver-Side Air Bag

Activity Calculations

Moles of CO2 required to inflate 80-L driver-side air bag at room temperature and pressure

Balanced equation for the reaction of NaHCO3 and CH3COOH to CO2

Mass of NaHCO3 needed for the reac- tion (84.0 g/mol)

Volume of vinegar required (0.833 M acetic acid)

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ACTIVITY

ACTIVITY 3 continued Data Table 4: 160-L Front Passenger-Side Driver Air Bag

Activity Calculations

Moles of CO2 required to inflate 160-L front passenger-side air bag at room temperature and pressure

Balanced equation for the reaction of NaHCO3 and CH3COOH to CO2

Mass of NaHCO3 needed for the reaction (84.0 g/mol)

Volume of vinegar required (0.833 M acetic acid)

Disposal and Cleanup 1. Dispose of plastic bags, plastic spoon, and

weighing boat. 2. Rinse graduated cylinder, dry with paper

towel, and return to equipment kit. 3. Clean counter space. 4. Leftover baking soda and vinegar should be

returned to the chemical kit.

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NOTES

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CB780111609

CHEMISTRY Engineering a Better Air Bag

Investigation Manual

www.carolina.com/distancelearning 866.332.4478

Carolina Biological Supply Company www.carolina.com 800.334.5551 ©2016 Carolina Biological Supply Company

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Engineering a Better Air Bag
Table of Contents
Overview
Objectives
Key
Time Requirements
Background
Materials
Included in the materials kit:
Needed from chemical kit 1:
Needed from the equipment kit:
Safety
Preparation
ACTIVITY
ACTIVITY 1
A Stoichiometry of Reactants and Products
ACTIVITY 2
A Testing Model Air Bags
ACTIVITY 3
A Amount of CO2 for Full-Size Air Bags
Disposal and Cleanup
NOTES