Making sulfuric acid is simple and fun and it will put you in touch with the most important chemical of modern times. We could make it under glass bells like Spot did or we could make it in lead chambers like Roebuck did, but both of those methods would be more trouble than they'd be worth, given that we just want to make enough acid to show that we can. So we're going to use the same container we always do when we need a cheap, convenient container: the 2-liter pop bottle. You might call this the Pop Bottle Chamber Process for sulfuric acid manufacture.

We need two reactors, a burner and an absorber. You can make a nifty burner from a pop bottle cap, a threaded steel rod, four nuts, and a copper plumbing fitting called an endcap. For the absorber you can use a 2-liter pop bottle. The sizes don't matter as long as the endcap will fit into the mouth of your pop bottle. I use a half-inch endcap and an eight-inch length of quarter-inch threaded rod. Drill a hole in the center of the endcap to fit the threaded rod and secure it with one nut inside and one nut outside the endcap. Do the same thing at the other end of the rod with the pop bottle cap. The open ends of the two caps should face each other, like it shows in Figure 18-2.

Figure 18-2. The Sulfur Burner

You should operate your reactor outdoors or in a fume hood, because the smell of burning sulfur is pleasant only to a select few. Wash out the pop bottle and add 4 mL of water to it. Place 0.5 g of sodium nitrate into the copper endcap and then put 0.5 g of sulfur on top of the sodium nitrate. Light the nitrate/sulfur mixture by holding your burner over a spirit lamp or Bunsen burner. Hold the burner by the pop bottle cap because the threaded rod is going to get hot. The sulfur will turn black and melt into the sodium nitrate and then the nitrate will start to puff up and crackle as it decomposes. The nitrate/sulfur mixture will catch fire, but leave it over the lamp until it is really going good. Then carefully insert the burning endcap into the mouth of your pop bottle and screw the cap down tight. The bottle will start to fill with dense fumes of sulfur dioxide and nitrogen oxide. If you can, take your bottle into a dark corner to check whether your burner is still burning. If it goes out, carefully remove it from your pop bottle and light it over the spirit lamp again. Reinsert the flaming endcap into your pop bottle and repeat the cycle until it will no longer light. Remove the burner from your pop bottle and screw a fresh bottle cap onto the pop bottle. When the burner has cooled you can rinse the small amount of residue into a sink.

Figure 18-3. The Pop Bottle Chamber

You might think that the reaction is over, but it's only just begun. The bottle is now filled with sulfur dioxide, nitrogen oxide, oxygen, and of course, nitrogen. Over the course of the next few hours, the nitrogen oxide will catalyze the reaction of sulfur dioxide with oxygen, producing sulfur trioxide, which will dissolve in the water to form sulfuric acid. You will know that this is happening because as the oxygen is consumed and the sulfur trioxide dissolves, the bottle will start to collapse and the fog that fills the bottle will clear. You can speed up the process by opening the cap to admit more air and then sealing the cap again. If you leave the absorber to sit overnight, the acid product will be virtually odorless since all of the sulfur oxides will be gone. Whether you wait an hour or let it sit overnight, you can test your acid by opening the pop bottle and pouring its contents into the bottle cap. Test the liquid with pH test paper, the chemist's virtual tongue; if you have been successful, it should turn bright red. Congratulations! You have just manufactured the most important chemical of modern times. If you were in business, you would distill your dilute acid to separate the water from the acid. But given that this is just a test run producing dilute acid, you can pour it down the drain when you are done with it. After all, it is drain opener.

If you are interested in further exploration, try repeating the process without the sodium nitrate. You will find that the bottle does not collapse, the fog clears very slowly, and the resulting acid smells strongly of rotten eggs. I suggested a 50/50 mixture of nitrate and sulfur because there is limited oxygen in our small absorber. In commercial lead chambers, the usual ratio was 1 part nitrate to 7 parts sulfur. The nitrate ratio affects only the rate of the reaction, not the amount. In early chamber plants, nitrogen oxide went up the smokestack as a waste product, but from about 1840 the Gay-Lussac tower was used to recover nitrogen oxides. This practice reduced the nitrate consumption, making the process more economical. Also from the 1840's, sulfur dioxide from roasting pyrite ores (Equation 9-2) began to be used as an alternative to sulfur. Thus sulfuric acid turned out to be a good sideline for lead, copper, and iron smelters.

ImportantQuality Assurance

Record in your notebook the amounts of sodium nitrate, water, and sulfur you used. Describe the reactor and its operation. Note how long you waited to test your acid, whether additional air was allowed into the absorber, and whether or not your acid product had a strong smell. Tape your red pH test paper into your notebook as a keepsake.