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Experiment 15: Hydrogen Boom


30 March 2010 by Quest 2, to link in with Chapter 15 of our book. (This experiment was done a week later than planned because important homework had not been completed.)


To see if hydrogen will seep out of rubber balloons.

To produce a boom from hydrogen.


  • Sodium hydroxide is very caustic.
  • The reaction of aluminium with sodium hydroxide is very exothermic. If a plastic bottle is used a lot of extra cooling (eg, cold water) will probably be required.
  • Hydrogen burns with an almost colourless flame. It can be very hard to see during daylight.
  • The glass bottle should never be stoppered.
  • Most of this experiment should be done outdoors, preferably in a shady location away from flammable objects.
  • A supply of fresh water such as a full bucket or a hose should be close at hand.
  • Safety goggles should be worn for the entire experiment, as well as rubber gloves for those handling sodium hydroxide.
  • Hearing protection should be worn when attempting the bits likely to be particularly noisy.

Sodium hydroxide burn.


The standard laboratory test for hydrogen is the pop test. If hydrogen is present in an upside down test tube (because hydrogen is lighter than air), a lit splint inserted into the test tube will ignite the hydrogen resulting in a squeaky pop. The splint will be extinguished.

Hydrogen gas has a very small molecule and containing it can be difficult.


Aluminium is actually a very reactive metal, but under normal circumstances aluminium does not react with water because an impermeable protective layer composed of aluminium oxide (Al2O3) either forms within seconds or is already in place. This means that strong nitric acid can be transported in aluminium containers quite safely.

Solid sodium hydroxide doesn't react with aluminium (sodium is more reactive than aluminium and is already bonded to the hydroxide ion), but the layer of aluminum oxide previously formed by passive corrosion can be dissolved with sodium hydroxide in solution.

Al2O3(s) + 2 NaOH(aq) + 3 H2O(l) → 2 Na+(aq) + 2 [Al(OH)4]-(aq)

This allows the reaction of aluminium and water to take place, but until the protective layer has been removed it occurs relatively slowly. Aluminium hydroxide, Al(OH)3, Alum, is the most stable form of aluminium in normal conditions.

2 Al(s) + 6 H2O(l) → 2 Al(OH)3(s) + 3 H2(g)

Aluminium hydroxide is amphoteric. It dissolves in acid, forming [Al(H2O)6]3+ (hexaaquaaluminate) or its hydrolysis products. It also dissolves in strong alkali, with the OH- ion (in this case from the sodium hydroxide) forming the soluable [Al(OH)4]- (tetrahydroxoaluminate).

Al(OH)3 + NaOH(aq) → Na+(aq) + [Al(OH)4]-(aq)

So with plenty of water the overall reaction is

2 Al(s) + 6 H2O(l) + 2 NaOH(aq) → 2 NaAl(OH)4(aq) + 3 H2(g)

The aluminium completely dissolves and the water acts here also as an acid. With less water the aluminium makes a solid.

2 Al(s) + 6 H2O(l) + 2 NaOH(aq) → 3 H2(g) + 2 NaAl(OHOHOHOH)(aq)

2 Al(s) + 2 H2O(l) [ + 4 H2O(l) ] + 2 NaOH(aq) → 3 H2(g) + 2 NaAlO2(aq) [ + 4 H2O(l) ]

2 Al(s) + 2 H2O(l) + 2 NaOH(aq) → 2 NaAlO2(s) + 3 H2(g)


  1. Place a small amount of solid sodium hydroxide in a test tube. Add a small amount of aluminium foil. Observe. Add a small amount of water and swirl to dissolve the sodium hydroxide. Observe. Capture the gas released with an upsidedown test tube. Attempt to light captured gas.
  2. Make a larger solution of sodium hydroxide in a glass bottle. Add a "sausage" of aluminium foil. Light gas released. Light some paper with the hydrogen flame.
  3. Stretch a balloon over the neck of the bottle and allow the balloon to inflate. When sufficiently inflated measure its diameter. Tie the balloon, measure again. Hold the balloon in wooden test tube holder at arm's length. Someone else light the balloon using BBQ lighter, also at arm's length.
  4. Repeat with heart shaped balloon.
  5. Repeat with round balloon. Attempt to get balloon larger.
  6. Repeat using pieces of an aluminium can.

Make fresh sodium hydroxide solution in the bottle as required.

Materials & Equipment

  • Sodium hydroxide, NaOH.
  • Aluminium foil, Al.
  • Water, H2O.
  • Safety goggles.
  • Rubber gloves (for handling caustic material).
  • Leather gloves (for handling hot objects).
  • Ear muffs or ear plugs.
  • Test tubes and holder.
  • Beaker.
  • Water jug.
  • Pipette.
  • Wooden board.
  • BBQ lighter.
  • Glass bottle.
  • Funnel.
  • Paper.
  • Rubber balloons.
  • Ruler or tape measure.


  1. No change occurred when just NaOH and Al was in the test tube. When water was added there was no change initially, then it started bubbling, getting more energetic as more time passed. The captured gas combusted with a quiet squeaky pop.

  2. This was actually done later in the experiment. Much of the time the flame was very hard to see and it was hard to tell if it was still lit, but a piece of paper lit from it showed it was still alight.

  3. The initial solution in the bottle was too weak, so the balloon was taken off and more NaOH was added. When the balloon was put on the bottle again it was initially hard to get a good seal between the balloon and the neck of the bottle. The balloon was hard to measure because it decreased in size so quickly after taking it off the bottle. By the time it was tied it was already much smaller, and smaller still by the time it was lit.

    Time (seconds) Action Approximate balloon
    diameter (cm)
    0 Taken off bottle 10
    ~30 Lit 8

    The balloon exploded with a loud pop and James says it "looked like a fireball". Kent, who lit it, was particularly surprised, as he didn't think it would work anywhere near as well as it did. After tipping the waste liquid down a drain Kent said the liquid was "pretty hot".

  4. The bottle was almost too hot to hold the heart shaped balloon onto while wearing leather gloves. When the balloon was lit it developed a hole near its base which spit burning hydrogen out with a whistling noise, with a slightly visible orange flame.

    A second attempt with a heart shaped balloon resulting in a split in the neck of the balloon while it was on the bottle.

  5. The next round balloon was much larger when on the bottle but went down very quickly when taken off, so it was not much larger than the previous attempt by the time it was lit.

    Time (seconds) Action Approximate balloon
    diameter (cm)
    0 Taken off bottle 17
    ~15 Tied 12
    ~30 Lit 10

    The balloon exploded with a louder pop than previously, along with an orange fireball that the young chemists described as quite large and Mrs D (from a safer distance) described as quite small.


  • Aluminium and concentrated sodium hydroxide solution are an effective way of making hydrogen.
  • The reaction makes a lot of heat.
  • The reaction takes a little bit of time to get going, and occurs much faster with concentrated NaOH solution.
  • A hydrogen flame is very hard to see unless it has burning rubber in it.
  • Hydrogen is hard to contain in old rubber balloons; it seeps out quickly.
  • Aluminium from a drink can does not react very quickly, even in concentrated NaOH solution.
  • Leather gloves are handy for holding hot objects but do not provide good finger dexterity.
  • Better quality balloons are needed.