24.3.

 

It rises from the Earth to Heaven and descends again to the Earth, and receives power from Above and from Below. Thus thou wilt have the glory of the Whole World. All obscurity shall be clear to thee.

 The Emerald Tablet of Hermes Trismegistos

A lime kiln, a slaker, a still, two absorbers, and a furnace make up the complete Solvay process. None of this is new; you have known how to make lime since Chapter 10; you grasped the secrets of distillation in Chapter 16; you learned how to build an absorber in Chapter 18; and the final furnace is quite similar to the one described in Chapter 20. You could build the whole plant out of pottery and soft-drink bottles if you wanted too, but I am afraid that few readers will want to go to all that trouble to produce something that might have been extracted in one step from seaweed ashes. After batteries, dyes, and photographs, the prospect of making one white powder from another might be a little bit anti-climactic. So how about a seance? Let us conjure some spirits, materialize some ghosts, bottle some genies, herd some bejeesical cats. Let us make some ammonium bicarbonate. Okay, so it is not going to be the perfect birthday present for Mom. You are not going to save a bottle of it for graduation day or mount it on your key-chain. Look, nobody is holding a gun to your head; if the prospect of making something "rise from Earth to Heaven and descend again to the Earth" does not float your boat, then go directly to the next chapter; do not pass "Go," do not collect the glory of the Whole World.

For anyone who made it past the last sentence, let us see whether we can clarify some obscurity. You have been using ammonia since Chapter 12, whether home-grown or store-bought. You are undoubtedly familiar with ammonia's unmistakable aroma, but how does it get from the bottle to your nose? The stuff in the bottle is an aqueous solution of ammonium hydroxide, NH4OH. Escaping from the bottle is bejeesical ammonia, NH3, the gas which makes your eyes water. Unfortunately, the word ammonia is often used indiscriminately to describe both the gas and its solution. Commercial ammonium hydroxide is 28-30% ammonia in water; household "ammonia" is more dilute. For this project we need gaseous ammonia, which we can get by distilling household ammonia.

In addition to ammonia, we need some carbon dioxide. In the industrial process this comes from the lime kiln, but we can use the carbon dioxide collected in Section 4.3 for this very purpose. Figure 4-3 details the fermentation lock consisting of a balloon glued to a bottle cap with a hole in it. This balloon is either still screwed onto your mead or you have wrapped its neck around and pencil and secured it with a twist tie. You will need a minimum of 2 L of carbon dioxide. If your balloon is round, measure its circumference with a piece of string; the circumference should be at least 50 cm. If your balloon is oblong it should be at least as big as a 2-liter soft-drink bottle. With your balloon of carbon dioxide handy, it is time to distill your ammonia.

Figure 24-2. Distillation and Absorption

Set up your still just as you did in Chapter 16, but instead of filling your Erlenmeyer flask with mead, fill it with 400 mL of household ammonia and a few boiling chips. For the receiver you can use our old friend, the 2-liter soft-drink bottle. Since we are collecting a gas there is no need to cool the receiver; there is no need for ice. Slip the receiver over the condenser tube and place the still on a hot-plate. Set the hot-plate power to "high," but as soon as the pot begins to boil turn the power down to half. Adjust the hot-plate power to keep the pot boiling without taking the head temperature above 82C (180F); you want to distill gaseous ammonia, not water. If you are not paying attention, the head will climb too high, too fast, and you will have to start over. If, however, you separate the gas by fire, the fine from the gross, gently and with great skill, then the head temperature will climb gradually to 82C. You will notice what looks like steam condensing on the sides of the receiver; this is concentrated ammonium hydroxide. Allow a few mL to collect in the bottom of the receiver and then shut down the distillation. Remove the receiver from the still, drain the ammonium hydroxide into a small beaker, and using a graduated pipette or graduated cylinder pour 2 mL of ammonium hydroxide back into the receiver. The reason for returning this ammonium hydroxide will be explained shortly.

Once the ammonia distillation is complete, transfer the balloon from your mead to your receiver as quickly as possible. Pinch the neck of your balloon, unscrew it from your mead, screw it onto the receiver, and release the neck of the balloon. Over the course of a few minutes bejeesical carbon dioxide will be absorbed by the ammonia; your receiver has miraculously changed into an absorber. The balloon will shrink as carbon dioxide becomes carbonic acid, as shown in Figure 24-2(R). The bottle will get hot as carbonic acid reacts with ammonium hydroxide to form ammonium bicarbonate. Roll the bottle from side to side to keep the walls wet. You will notice what looks like condensation on the inside of the bottle, but as the reaction proceeds this condensation will sprout crystals, as shown in Figure 24-3(L). While your crystals are growing, let us take a look at the stoichiometry.

CO2(g) + NH3(g) + H2O(l) = NH4HCO3(s)

At room temperature and normal atmospheric pressure a mole of gas occupies 24.5 liters. This unit factor, (24.5 L/mol CO2) or (24.5 L/mol NH3) allows us to answer stoichiometric questions:

Q: How many grams of ammonium bicarbonate can be produced from the reaction of 3.0 L of carbon dioxide with excess ammonia and water?
Q: How many grams of ammonium bicarbonate can be produced from the reaction of 2.0 L of ammonia with excess carbon dioxide and water?
Q: How many grams of ammonium bicarbonate can be produced from the reaction of 2.0 g of water with excess ammonia and carbon dioxide?

Figure 24-3. Spirit Made Flesh

So what is the theoretical yield, 22.6 grams? No, to produce 6.4 g of ammonium bicarbonate you need 2.0 L of carbon dioxide and 2.0 L of ammonia and 1.5 g of water. If you have 2.0 L of ammonia you can make at most 6.4 g of ammonium bicarbonate, no matter how much carbon dioxide and water are present. In this case the limiting reagent, the one which runs out first, is ammonia and the theoretical yield is 6.4 grams. If your balloon holds less than 2.0 L of carbon dioxide it will completely collapse; in this case carbon dioxide is the limiting reagent and your theoretical yield will be somewhat less than 6.4 g. Similarly, if there is less than 1.5 g of water present, water is the limiting reagent. We added 2 mL of ammonium hydroxide (ammonia in water) to ensure that there would be enough water present. Adding more ammonium hydroxide might have increased our yield since it supplies both water and ammonia, but we would have wound up with a solution of sodium bicarbonate rather than crystals. Limiting the water allowed us to collect crystals immediately without having to wait for the excess water to evaporate.

When the balloon stops shrinking and the bottle is cool, remove the balloon and cut the bottle open at the shoulder. Use a spoon or spatula to push the ammonium bicarbonate crystals to the bottom of the bottle. Trim away the walls of the bottle as you go until you are left with a shallow dish filled with crystals, as shown in Figure 24-3(R). Allow your crystals to dry overnight and then weigh them to get your actual yield, which is often expressed as a percentage of the theoretical yield.

Consider what has happened here; you started with an empty bottle; everything that went into the bottle was a gas, yet from these bejeesical spirits a solid body emerged. As an infant it smells of ammonia but when you allow it to dry overnight the smell almost goes away. It has so much potential; it might make bread or cake or soda, but this particular body is destined for a trial by fire. Place it into a small beaker and heat it with a hot-plate or spirit lamp and as it gets old and decrepit it will begin to smell of ammonia once more. It begins to lose weight and finally just fades away, departed once more into the spirit world. In the end, the only thing left of it is a story.

ImportantQuality Assurance
 

Include in your notebook safety information for ammonia, carbon dioxide, and ammonium bicarbonate. Record the actual yield of ammonium bicarbonate expressed as a percentage of the theoretical yield. Include a photograph of your crystals to illustrate your telling of their poignant saga.