A Reactivity Example Problem

A train has collided with a truck at an intersection in the industrial section of a major city. A tank car and a flatbed car filled with containers have derailed. Now the tank car is lying in a ditch alongside the tracks, surrounded by some containers that have broken loose from the flatbed car.

• The tank car is labeled "hydrogen fluoride."
  
• The UNNA number shown on all the containers is 1806. (The UNNA number is the United Nations-North America number. This numbering system was developed by the U.S. Department of Transportation, and has since become the UN standard system for classifying hazardous materials.)

If you were responding to this incident, you would want to know:

What problems could occur if these chemicals were to be mixed together when crews right the tank car and collect the containers?

You can use the Worksheet to answer this question, as described below.

Working the Problem

First, download and install the Worksheet, if you haven't already done so, then start it. (See the Downloading link at page bottom.)

1. Click Next to view the Mixture Worksheet. You'll "mix" the two chemicals by finding them in the database and adding them to the Mixture Worksheet. The Worksheet will then predict the mixture's potential reactivity:
   
   
   
   Next, you'll need to search the database for each of the two chemicals you want to add:

2. Perform a basic search for chemicals with names that include "hydrogen fluoride." To do this, click Add a Chemical, then type "hydrogen fluoride" in the "Search for" text box:
   
   
   
   Then click Start Search.

3. Scroll through the list of five chemicals found to find hydrogen fluoride. To scroll forward through the list, click the right-hand arrow in the upper right corner of the card window:
   
   

4. Hydrogen fluoride is the third of the five chemicals. Check the information about the characteristics of hydrogen fluoride. First check the Special Hazards list to see the especially acute hazards (this list shows that hydrogen fluoride is both water- and air-reactive). Next, check
   • Air & Water Reactions to learn more about its reactions with air and/or water.
     
   • General Description to learn its general physical characteristics.
     
   • Chemical Profile (click Additional Information to see this section) to learn about past accidents involving hydrogen fluoride.
     
   • Belongs to Reactive Groups (click Additional Information to see this section) to find out which reactive groups include hydrogen fluoride.

5. Click Add This Chemical to Mixture to add hydrogen fluoride to the Mixture Worksheet:
   
   

6. Perform an advanced search for chemicals with the UNNA number of 1806. To do this, click Add a Chemical, then click Advanced Search. Set up your search so it looks like the picture below, then click Find:
   
   

7. This time, you'll find just one chemical, phosphorus pentachloride. Check its characteristics, and then click Add This Chemical To Mixture to add it to the Mixture Worksheet.

8. Check the Mixture Worksheet to see statements about the mixture's potential reactivity:
   
   

These statements tell you that the response team would need to be prepared for a possible explosion and release of a toxic gas, if the two chemicals were to accidentally mix. (The toxic gas that would be liberated in this reaction would be hydrogen chloride, but the Worksheet doesn't report this.)

As you plan your response to this accident, double-check the information specific to each chemical to learn more about potential hazards. Scroll down to see listings reminding you of the Special Hazards of each chemical in the mixture. To review all information about each chemical, in the Mixture Worksheet, click on the name of either chemical, then click More Info on Selection. (Once you've reviewed the information, click Cancel to return to the Mixture Worksheet.)

To learn more about how to interpret the results you obtain from the Worksheet, check our list of Tips for Worksheet Users (link below).

Final Note: In this exercise, you "mixed" two chemicals together to learn about their potential reactivity hazard. You can add more than two chemicals to a mixture. But whenever you do so, be aware that the Worksheet only predicts the potential reactivity between two chemicals at a time (to predict the reactivity of a mixture of more than two chemicals, it predicts the reactivity of all possible pairs). This means that the Worksheet can't recognize situations when more than two chemicals react together.