Question:
I am doing a high school project on soda-acid fire extinguishers. I am supposed to talk about what makes fire extinguishers work and why soda-acid fire extinguishers are obsolete. I am also supposed to make a soda-acid fire extinguisher.

Answer: They work because when you tip them over, an internal container of diluted sulphuric acid mixes with a solution of sodium bicarbonate (baking soda) or sodium carbonate (washing soda) (I don't remember which sodium compound is used.) A chemical reaction takes place, releasing carbon dioxide gas. The gas increases the pressure in the tank. The hose is connected near the bottom of the (inverted) tank, so the pressure forces the mixture out the hose.

Why are they obsolete? Consider this: there are several classes of fire. Class A: Wood, paper, cloth, etc.; Class B: Oil; Class C: Electrical; and Class D: Combustible metals (?) like magnesium.

Classes A through C are the most common ones to occur in homes and schools. The soda-acid extinguisher should work fine on Class A fires by wetting the burning the material. But for Class B, the mixture, which is mostly water, might only cause the fire to spread. And for Class C fires, the mixture might really be bad news, because the mixture is electrically conducting. There are other types of fire extinguishers around that can handle Classes A, B, and C. (Look up "fire extinguisher" in a decent encyclopedia and read about them.)

To make a simple fire extinguisher, you need somethingair-tight, otherwise the CO2 will leak and fail to push on the mixture enough. For acid, be very careful! Concentrated sulphuric acid is extremely dangerous, and diluting it should only be done by someone who knows how to do it properly. Even the diluted form should be treated with respect, lest it get in your or someone else's eye. You could use something safer, like vineger, which also releases CO2 when added to a solution of NaHCO3 or Na2CO3. Sodium bicarbonate is probably more readily available to you than sodium carbonate, and should work well. Try out your extinguisher several times before demonstrating it in class, and keep notes so you know how much of each thing to mix to get a decent demo