[IndianCheese]

My chemistry teacher gave us this end-of-year bonus assignment.  He held up an empty water bottle and said "Using as many things you have learned this year as you can, come up with a way that you could theoretically pop (blow up) this bottle."  (He likes to relate chemistry to real-life things and how it can actually be used for things.)  He also warned us not to actually do it for our safety.  I wanted to check with you guys to see what you think.  Mine involves solubility, electrochemistry, and pressure.

Materials:
Water
Salt
Aluminum foil
5 9volt batteries
Cellophane
Bottle with screw-on lid
Rubbing alcohol
Lighter
A big-*ss pair of balls

Fill bottle with 0.5 mL of water.  Add 87.5 g of salt to it (approximate max grams that will dissolve).  Wrap 9volt batteries in cellophane, exposing only the poles.  Connect batteries into a chain at the poles, but do not complete the circuit.  Jam one large aluminum foil balls onto each of the 2 free poles.  Drop this into the bottle.

From what I have learned, this would theoretically happen.

When the battery/foil contraption hits the salt water, the circuit would be completed and electrons would start flowing.  The anode would attract the sodium ions and attempt to form sodium metal, but would instantly react with the water to form sodium hydroxide and hydrogen gas.  The sodium hydroxide would then begin to react with the aluminum foil (which is serving two purposes: being the anode, and serving the following reaction) to form even MORE hydrogen gas.  On the other side, the chlorine ions would begin to move towards the cathode, react to form Cl₂, and result in chlorine gas.  All of this gas SHOULD continue to build and build and build until one of two things happen: the batteries unfortunately die (), or the bottle bursts with the sound of a shotgun crack.  It is essentially a sort of Drano bomb, but on steroids.

In addition, the same MIGHT occur if you just dropped a few batteries into a bottle of salt water if you don't feel like going through the aluminum/cellophane stuff (however, sodium hydroxide would be produced and would not be able to react with the aluminum to produce the additional hydrogen gas).

What do you think?

[UnintentionalChaos]

Under pressure, almost all of the chlorine would be reabsorbed and react with the NaOH, making NaOCl and NaCl (this is how bleach is made). This will attack the aluminum foil (and the battery, probably killing the reaction prematurely)

[IndianCheese]

What if I used salt substitute (potassium chloride)?  Since that would make KOH instead of NaOH, would that change the bleach-making reaction at all?

[UnintentionalChaos]

Potassium behaves (in most ways, especially in terms of salts) exactly like sodium. You'd form potassium hypochlorite instead of sodium hypochlorite. I'd try to use as little liquid as possible to achieve what you want.

[Donaldson Tan]

When the battery/foil contraption hits the salt water, the circuit would be completed and electrons would start flowing.  The anode would attract the sodium ions and attempt to form sodium metal, but would instantly react with the water to form sodium hydroxide and hydrogen gas.

That is themodynamically impossible to achieve with batteries.

[Borek]

When the battery/foil contraption hits the salt water, the circuit would be completed and electrons would start flowing.  The anode would attract the sodium ions and attempt to form sodium metal, but would instantly react with the water to form sodium hydroxide and hydrogen gas.

That is themodynamically impossible to achieve with batteries.

But the final conclusion - hydrogen evolution and hydroxide production - is nonetheless correct. Just there is no sodium metal step.

[DrCMS]

Back to the orginal question would the 9V batteries even fit into the bottle?

Why not use a reaction between say acid and a carbonate that generates CO₂ to pop the bottle?

[The Tao]

Why don't you just drive to a really high mountain with the bottle sitting in your trunk.