Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Return to stao.org CRUCIBLE online Airbags: Is There a Price Limit on Safety? ««« By Susan Miller Susan was a preservice teacher at the University of Western Ontario when she wrote this article. Susan was a recipient of the 2007 STAO Preservice Award for this submission. Curriculum Connetion: SCH3U, Quantities in Chemical Reactions & SCH4C, Chemical Calculations units. The following activities and worksheets were developed for the SCH3U, Quantities in Chemical Reactions & SCH4C, Chemical Calculations units. The aim is to allow the student to become aware of the uses of stoichiometry in everyday situations and to further their critical thinking process by discussing an issue with which they are familiar. Airbag technology was 30 years in development before it was considered safe and reliable enough to employ in cars. However, with increased safety, there is an increased cost of insurance associated with vehicles due to the high costs of repairs. In addition, there are still safety concerns for underweight and under-height passengers and environmental concerns with disposal of airbags after deployment. take for their own safety through the use of other safety features such as seat belts. In short, is the safety benefit of having airbags fitted in cars outweighed by the high cost of insurance, deaths on inflation and environmental concerns with disposal even for a low-speed collision? The lesson begins with an introduction to airbags, using the newspaper style article included in this lesson plan. Questions are provided at the end of the article to help focus student discussion. The students will be given one of six hats, (creativity, bad points, good points, organization, emotions and information) and be required in their group to come up with supporting stances for their hat. Then, in a group that has one representative with each type of hat (6 in the group in total), students will discuss their position. Time may also be taken to conduct Internet searches to support their positions. The teacher may want to It is well-known that airbags save lives and prevent serious injuries when cars are involved in high-speed accidents. In this activity, however, students are encouraged to consider the implications of cost versus safety in a lowspeed collision. Students are asked to evaluate whether the higher costs of repairs and disposal concerns associated with airbags are validated by increased safety. Furthermore students are asked to consider whether there is a level of personal responsibility that one should Airbags: Is there a price limit on safety? Volume 39 • 2 November/December 2007 Return to stao.org CRUCIBLE online include information about the cost of repairs for a vehicle involved in a low-speed collision and the discussion about the costs of insurance rates, if known. Students are asked to consider following stakeholders in their discussion and evaluation of this issue: • Car drivers and passengers – safety versus expensive insurance costs • Insurance companies – expensive repairs, use of used airbags instead of new • Environment – recycling/disposing of used airbags. The final activity is to write a letter to the editor of a news- paper, voicing their opinion on the airbag article. In this case, the student may take the stand they wish. This activity fits nicely with the ministry expectations for this unit as students are able to see the application of chemical quantities and calculations in an example with which they will be familiar. The letter to the editor provides a valuable chance for students to demonstrate science literacy. In addition, the stoichiometry pages that follow this discussion provide concrete examples of the importance of chemical quantities and valuable practise exercises on a real case. Airbag Chemistry In the 1980s, Lee Iacocca warned of problems surrounding the development of airbag technology. He was concerned that people would consider wearing seat belts unnecessary and about the general safety of the technology itself. higher if the airbags are deployed. Upon detonation, the fabric on the dash is torn and therefore must be replaced. On modern cars, the labour involved in re-setting the dashboard electronics is intensive and therefore the cost is significant. New airbags typically cost around $800-$1000. Although many advances have been made to allow more flexibility in the use of airbags, these systems were developed for the 1.72m, 82kg male sitting 25cm from the steering wheel. Women and children under 1.5m tall and weighing less than 50kg have been injured. ed to produce nitrogen gas and sodium. The nitrogen gas is used to fill the airbag and protect the passenger. Sodium is, however, a very reactive metal (it may be sodium hydroxide if there is moisture in the airbag) and therefore must be reacted to allow for safe disposal. Airbag technology was patented in 1953. The reaction involved is an explosion, similar to that used to launch the space shuttle. It took 30 years to develop and refine the technology to allow for safe inflation in 40 milliseconds. When a car is involved in a collision, the sensors must be able to distinguish between a minor bump and a crash. A magnet holds a ball in place. If a car decelerates quickly, a ball is released from the magnets. This connects an electrical circuit and this connection causes the airbag to be deployed. The following chemical reactions occur in sequence upon detonation of an airbag: 1. 2NaN3 → 3N2 + 2Na 2. 10Na + 2KNO3 → N2 + 5Na2O + K2O 3. 2K2O + SiO2 → K4SiO4 2Na2O + SiO2 → Na4SiO4 In the first reaction, sodium azide is ignit- In the second reaction, the sodium is reacted with potassium nitrate, releasing more nitrogen and two more dangerous oxides that must be neutralized. The final stage involves the reaction of potassium oxide and sodium oxide with silicon dioxide to produce silica glass. Until an airbag is completely neutralized, it is an environmental hazard and must be handled with caution. Airbags are set to deploy at a minimum of 30km/hr, a speed that could cause significant injury if a passenger was not wearing their seat belt, but unlikely to cause serious injury if properly belted in. If a vehicle is involved in a minor crash, the cost of repairs is likely to be 50% Airbags: Is there a price limit on safety? – Page 2 In conclusion, it seems clear that airbag technology has resulted in fewer fatalities from high-speed collisions. New advances are making their deployment safer all the time. However, safety comes at a cost, including higher rates for insurance, injury on inflation and environmental concerns with disposal. Review Questions: 1. What are some of the disposal concerns for detonated and intact airbags? 2. Should passengers have the option of turning off airbags at their discretion? 3. Current deployment speed is set to around 30 km/hr. Given the high costs of repairs & insurance, is this set too high or too low? Volume 39 • 2 November/December 2007 Return to stao.org CRUCIBLE online Cost of Repairs PARTS QTY DESC. UNIT PRICE- 1 1 1 1 1 1 1 1 1 1 8 2 1 1 1 1 1 1 NPC NPC NPC NPC NPC NPC NPC NPC WOODSTO-CK WOODSTO-CK NPC NPC COREYS COREYS CRSS CROS NPC NPC REBAR AIRBAG AIRBAG AIRDAM C/SPRING HOSE A/C LINE GRILLE RADIATOR CONDENSOR FREEZE BULBS DASH COLUMN HEADLIGHT FASCIA PRETENSIO PRETENSIO $332.00 $865.00 $670.00 $49.00 $70.50 $10.05 $117.00 $161.00 $180.00 $180.00 $2.88 $7.50 $600.00 $300.00 $205.61 $357.10 $92.25 $147.00 $332.00 $865.00 $670.00 $49.00 $70.50 $10.05 $117.00 $161.00 $180.00 $180.00 $23.04 $15.00 $600.00 $300.00 $205.61 $357.10 $92.25 $147.00 TOTAL - PARTS TOTAL - SUBLET $4,374.55 $262.95 TOTAL - SUPPLIES TOTAL - LABOUR SUBTOTAL: TAXES: TOTAL: $198.00 $5.00 $203.00 $2,061.00 $6,901.50 $966.21 $7,867.71 1 BODY SHOP MATERIALS 1 HAZARDOUS WASTE Airbags: Is there a price limit on safety? – Page 3 $865.00 $670.00 $49.00 $600.00 $300.00 $2,484.00 Volume 39 • 2 November/December 2007 Return to stao.org CRUCIBLE online Student Worksheet Airbag Chemistry When an airbag explodes, there are 3 different types of reactions that occur. Sodium azide produces nitrogen gas but there is a bi-product of Na. Na is very reactive and must be neutralized. For this, potassium nitrate is used. This creates two further compounds, sodium oxide and potassium oxide which must be neutralized by silicon dioxide. Chemical reactions: 1 Sodium Azide is ignited. Nitrogen gas fills nylon bag at 150-250 miles/hr NaN3 → N2 + Na 2. Sodium is very reactive and must be neutralized. Using the number of moles of Na produced from the first reaction, calculate using stoichiometry, Na + KNO3 → N2 + Na2O + K2O a) how many moles of Na2O are created? b) how many moles of K2O are created? 2 Reaction with potassium nitrate (1st stage to eliminating dangerous by-products) Na + KNO3 → N2 + Na2O + K2O 3. These products Na2O + K2O are also dangerous, and must further be neutralized by SiO2 to produce K4SiO4 and Na4SiO4 3 Reaction with sodium and potassium oxide to form silicate glass (2nd stage to eliminating dangerous by-products) K2O + SiO2 → K4SiO4 Na2O + SiO2 → Na4SiO4 a) What mass of SiO2 would be required in order to fully react with all of the of K2O from part (2)? K2O + SiO2 → K4SiO4 A typical 60L airbag requires 5.82 moles of nitrogen gas to fill it up. A manufacturer puts 65g of SiO2 in an airbag. Using stoichiometry, we are going to find out how many grams of SiO2 is required to completely neutralize the dangerous by-products of the airbag reaction & conclude whether 65 g is enough. 1. Use stoichiometry to calculate the number of moles of sodium produced by the first reaction if 378.3g of NaN3 is used. (Balance the equation first): NaN3 → N2 + Na Airbags: Is there a price limit on safety? – Page 4 b) What mass of SiO2 would be required in order to fully react with all of the of Na2O from part (2) Na2O + SiO2 → Na4SiO4 4. How much SiO2 is needed in total? Was 65 g of SiO2 enough? Volume 39 • 2 November/December 2007 Return to stao.org CRUCIBLE online Teacher answer sheet Airbag Chemistry (Solutions) 1. Use stoichiometry to calculate the number of moles of sodium produced by the first reaction if 378.3g of NaN3 is used. (balance the equation first): NaN3 → N2 + Na a) What mass of SiO2 would be required in order to fully react with all of the of K4SiO4 from part (2)? K2O + SiO2 → K4SiO4 2K2O + SiO2 → K4SiO4 2NaN3 → 3N2 + 2Na if 378.3g of NaN3 was used then 5.82 mol Na was produced. Ratio of 2NaN3 : 2Na is , thus 2/2*5.82 = 5.82 mol Na was produced by this reaction 2. Sodium is very reactive and must be neutralized. Using the # of moles of Na produced from the first reaction, calculate using stoichiometry, Na + KNO3 → N2 + Na2O + K2O 10Na + 2KNO3 → N2 + 5Na2O + K2O a) how many moles of Na2O are created? 5/10*5.82 = 2.91 1 *0.58 = 0.29 2 0.29 mol * (28.09+16*2) .29*60.06 17.42 grams of silicon dioxide (b) What mass of SiO2 would be required in order to fully react with all of the of Na4SiO4 from part (2) Na2O + SiO2 → Na4SiO4 2Na2O + SiO2 → Na4SiO4 1 2 *2.91 = 1.46 1.46 mol * (28.09+16*2) 1.46*60.06 87.39 grams of silicon dioxide (b) how many moles of K2O are created? 1/10*5.82 = 0.58 4. How much SiO2 is needed in total? 87.39+17.42 = 104.81 grams of silicon dioxid. 3. These products Na2O + K2O are also dangerous, and must further be neutralized by SiO2 to produce K4SiO4 and Na4SiO4 Airbags: Is there a price limit on safety? – Page 5 Volume 39 • 2 November/December 2007