Engineering Air Bag

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In this experiment, we inspect the airbag systems for the automobile industry. The vehicle industry has used the airbags composed of a chemical compound known as sodium azide (NaN3). However, environmental chemists have criticized the use of NaN3 due to its environmental air pollution since it is a toxic chemical. Engineers had been also faced with the hassle of dealing with the hot nitrogen gas that is supposed to inflate the airbag in the collisions. However, in the modern automobile vehicles, the airbag graph has been costumed to deal with the problem of the hot nitrogen gas. This test focuses on the alternative chemicals that may additionally be used which are less toxic and less expensive. Therefore, the acetic acid and sodium bicarbonate are used to produce carbon dioxide gas that inflates the airbag in the case of a collision that will prompt the reaction of the two chemicals. It should be noted that the reaction produces sodium acetate which is a harmless salt to the environment.

Material and Apparatus

Sodium bicarbonate

Acetic acid

Plastic spoon

250 ml beakers

Thermometer

Graduated cylinder, 50ml

Electronic balance

Weighing boat

6 resealed plastic bags

Procedure

Activity 1

Stoichiometry of Reactants and Products

This activity entails finding the exact amount that will inflate a sealed plastic bag after acetic acid reacts with sodium bicarbonate.

Activity 2

Testing Model Air Bags

Activity 3

Amount of CO2 for Full-Size Air Bags

Results and Discussion

Stoichiometry of Reactants and Products

Activity

Data and Calculations

Volume of 6 × 9-inch bag

1.2 Liters

Room temperature in Kelvin

Room pressure in atm

(“U.S. City Barometric Pressure Records”, 2017)

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

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

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

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

If 1 mole84g

0.0473 moles?

Volume of vinegar required (0.833 M acetic acid)

Mole ratio 1:1

If 0.883 moles 1000 ml

0.0473 moles?

Trial

NaHCO3(s)

Vinegar (ml)

Observations

1

3.9732

56.78

The gas fills the plastic bag

2

4.2732

59.78

The plastic bag fills more tightly than in trial one.

A white powder is seen in the plastic bag.

3

4.4732

66.78

A white sold is observed in the plastic bag

The plastic bag fills more tightly

The white powder observed is sodium bicarbonate which did not react since all the acetic acid was used up in the process. According to the law of mass action, increasing the quantity of reactants subsequently increases the products produced as depicted from trial 2 and 3 (Casiday & Frey, 2000).

Amount of CO2 for Full-Size Air Bags

80-L Driver-Side Air Bag

Activity

Calculations

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

Balanced equation for the reaction of NaHCO3 and CH3COOH to CO2

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

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

If 1 mole84g

3.1552 moles?

g

Volume of vinegar required (0.833 M acetic acid)

Mole ratio 1:1

If 0.883 moles 1000 ml

3.1552 moles?

ml

160-L Front Passenger-Side Air Bag

Activity

Calculations

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

Balanced equation for the reaction of NaHCO3 and CH3COOH to CO2

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

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

If 1 mole84g

6.3104 moles?

Volume of vinegar required (0.833 M acetic acid)

Mole ratio 1:1

If 0.883 moles 1000 ml

6.3104 moles?

ml

Pre-laboratory Questions

What does the term stoichiometry mean for a balanced chemical equation?

Stoichiometry defines the quantity of the reagents and products from a theoretical point of view of a chemical reaction.

What is the Ideal Gas Law?

It is an equation that indicates the relationship between the variables for gases. These variables include atmospheric pressure (P), moles of the gas (n), volume in liters (V), the temperature in kelvins (P) and a gas constant (R) (Timberlake, 2015). This law is given by,

Write a balanced equation for the reaction of sodium azide.

Explain how an airbag deploys when an impact of 10–15 miles per hour is detected.

The sodium azide pellets explode after the accelerometer closes a switch that ignites a charge. The nitrogen gas produced is responsible for filling the airbags at a velocity between 150 and 250 mph (Casiday & Frey, 2000). Since sodium metal reacts violently with water, a less reactive iron oxide is placed in the compartment to react with sodium. It should be noted that sodium azide has been used by engineers because the reaction takes milliseconds to start after an ignition.

Laboratory Questions

Does temperature make a difference in how much carbon dioxide gas is needed to inflate a 60-L air bag using the reaction of sodium bicarbonate and acetic acid? Compare a winter day at 0°C and standard pressure with a summer day at 35°C and standard pressure. Calculate the number of moles of carbon dioxide gas required for 60-L inflation at both temperatures and then calculate the percent difference in moles.

Winter Day at 0°C:

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

Temperature in kelvins = (0 + 273) K = 273K

Standard pressure = 1 atm

Therefore, the moles of carbon dioxide needed to inflate the airbag is given by,

Summer Day at 35°C:

Temperature in kelvins = (35 + 273) K = 308K

Standard pressure = 1 atm

Therefore, the moles of carbon dioxide needed to inflate

Percentage difference in moles

Difference in moles = (2.677 – 2.3728) moles = 0.3042 moles

Percentage difference in moles

Therefore, from the above working, it is evident from the difference of 11.36% that temperature affects the quantity of carbon dioxide required to fill an airbag. When temperatures are high, a lesser amount of reactants are required to inflate an airbag unlike when the temperatures are low.

Calculate the number of moles of nitrogen gas (N2) that are needed to inflate a 67-L driver-side air bag at standard temperature (0°C) and pressure (1 atm). Start by balancing the reaction shown below.

Solution

2NaN3 (s) → 2Na (s) + 3N2 (g)

Temperature in kelvins = (0 + 273) K = 273K

Standard pressure = 1 atm

Calculate the grams of sodium azide (NaN3) required to produce the number of moles of nitrogen gas calculated in Question 2.

Solution

2NaN3 (s) → 2Na (s) + 3N2 (g)

Mole ratio NaN3 (s): N2 (g) = 2:3

Therefore, the number of moles of sodium azide is obtained as follows,

Moles of NaN3 (s) moles

How many grams of sodium metal are produced in the decomposition of sodium azide shown in Question 2

Solution

Mole ratio NaN3 (s): Na (s) = 1:1

From the mole ratio, 1 moles of sodium azide produces 1 moles of nitrogen metal. Thus, to determine the mass in grams of sodium metal produced we proceed as follows,

Molecular mass of sodium = 23 g/mol

Moles of sodium = 1.9927

Mass = Molecular mass × moles

Mass of sodium metal = 23 × 1.9927 = 45.8321 g

General Lab Question

Based on the observed performance of the air bag models and the amounts of sodium bicarbonate and acetic acid (vinegar) needed for an automotive air bag of 80 or 160 L, are these reactants a good substitute for sodium azide? One additional note regarding sodium azide: the rate of inflation after a triggering impact is 40 milliseconds (0.04 s).

Even though the products formed after the reaction of sodium carbide reacts and acetic acid is environmentally friendly, it is not the best substitute for sodium azide. This is because sodium azide has a faster reaction time of approximately 40 milliseconds after a collision of significant impact has been detected. Also, 0.8 g of sodium carbide requires 11.26 liters for an automotive airbag of 80 L and 160 L which is a large amount as compared to that required by sodium carbide. For instance, the amount of sodium azide needed to fill 80 L automotive airbag is calculated below.

Solution

The amount of sodium azide required to fill 80 L of airbag considering the same conditions as that in the experiment,

2NaN3 (s) → 2Na (s) + 3N2 (g)

Pressure in atm = 0.9358 atm

Temperature = 289 K

Number of moles of nitrogen =

Mole ratio NaN3 (s): N2 (g) = 2:3

Therefore, the number of moles of sodium azide is obtained as follows,

Moles of NaN3 (s) moles

Molecular mass of sodium azide = 65 g/mol. Therefore,

If 1 mole → 65 g

2.1035 moles → ?

g

It is evident that the amount of sodium carbide is far much less as compared to the alternative method in the experiment for 80 L airbag.

References

Casiday, R., & Frey, R. (2000). Chemistry Behind Airbags. Retrieved from http://www.chemistry.wustl.edu/~edudev/LabTutorials/Airbags/airbags.html

Timberlake, K. C. (2015). General, organic, and biological chemistry: structures of life. Pearson Education.

U.S. City Barometric Pressure Records | Weather Underground. (2017). Retrieved from https://www.wunderground.com/resources/pressure_records.asp

Wetmore, J. M. (2008). Engineering with uncertainty: Monitoring airbag performance. Science and engineering ethics, 14(2), 201-218.

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