Stoichiometry and Real Life

 

If you saw the movie “Apollo 13” you saw an example of stoichiometry and problem solving in action.

 

Because of an accident, the Apollo 13 crew never got to land on the moon.

 

In addition, part of their oxygen supply was lost in the accident.

 

As a result, the crew was forced to “re-breathe” the cabin air.  The problem you are asked to consider is the fact that air breathed over and over again in a confined space becomes lower in oxygen and higher in carbon dioxide.  The carbon dioxide levels can become toxic very quickly, and the crew can asphyxiate.

 

Excess carbon dioxide can be absorbed or “scrubbed” from the air by a strong, solid base like lithium hydroxide.

 

Here are some questions for you to answer regarding Apollo 13’s lunar mission.

 

1.    What are the formulas for carbon dioxide and lithium hydroxide?

2.    What is the balanced equation for the reaction of these 2 chemical compounds?

3.    What phase (physical form) will the product(s) be in when the reaction is complete?

 

Human tidal volume (the volume of air that moves in and out of the lungs during normal quiet respiration is about 500 mL for an adult.  Total respiratory volume for an adult male is about 6000 mL.  Under the respiratory distress of increasing carbon dioxide, tidal volume may increase to as much as 3000 mL.  For the sake of argument, let’s use an average of 1400 mL for the tidal volume each of the three Apollo 13 astronauts.

 

Resting respiratory rate for adults is 12-18 breaths per minute (bpm).  Under stressful conditions, we would expect to be at the high end of that, so let’s use 18 bpm for our problem.

 

 For a human adult breathing normal air, inhaled air is about 0.04% or 0.3 mm Hg partial pressure carbon dioxide.  Exhaled air is approximately 5.2% or 40 mm Hg partial pressure carbon dioxide. The density of normal air is about 1.2g/L.

 

4.    Using the information given so far, calculate the number of grams of carbon dioxide exhaled in each breath (not counting what was inhaled.)

5.    What mass of carbon dioxide did all 3 astronauts exhale over a 5-day period?

6.    What mass of lithium hydroxide would be required to react with (absorb) all the carbon dioxide exhaled by the astronauts over 5 days?

7.    If the toxic level of carbon dioxide were 15 mm Hg, what would have been the minimum mass of lithium hydroxide necessary to keep the astronauts alive?

8.    Find the physical properties and cost of lithium hydroxide in one of the classroom reference books or on the Internet and suggest a possible reason why lithium hydroxide was used instead of sodium or potassium hydroxides.