Violent decomposition of hydrazine perchlorate

In this experiment, the perchlorate salt of hydrazine is made and allowed to crystallize and this salt is decomposed by heating it. This reaction is violent and spectacular, but also very beautiful. The experiment itself is very simple, provided you have the right chemicals.

Hydrazine perchlorate is quite stable on its own. It can be kept around without problems and it is stable. On heating, however, it quickly decomposes violently with a crackling noise and beautiful effects like spraying around of glowing fairy powder.

Required chemicals:

• perchloric acid, 20% solution in water

• hydrazine, 20% solution in water

Required equipment:

• test tubes
• glass rod
• pH paper (multi-range 4 ... 11)
• petri dish or hour glass

Safety:

• Perchloric acid at a concentration of 20% is moderately corrosive. Acid of much higher concentration, however, is highly corrosive and acid with a concentration of well above 70% can even cause explosions when it comes in contact with organic matter.
• Pure hydrazine is corrosive, prone to explosive decomposition and fumes in contact with air, but the 20% solution in water can be handled without any problem. Keep in mind though that hydrazine is a carcinogen and avoid exposure to its vapors.

Disposal:

• No waste should remain, all solid material can be decomposed above a flame.

Preparation of solid ethylene diamine perchlorate

One molecule of hydrazine combines with one molecule of perchloric acid. The salt with formula N₂H₅ClO₄ is formed. If the amounts below are used, then the synthesis certainly succeeds. Assure that no excess amount of perchloric acid remains. If excess hydrazine is present, then that simply evaporates. If excess perchloric acid is present, then a terribly hygroscopic and wet mess is obtained and no good dry crystals can be obtained, so it is best to assure a slight excess amount of hydrazine.

Take 2.5 ml of a 20% solution of perchloric acid and put this in a test tube.

Take 1 ml of a 20% solution of hydrazine. This is a slight excess amount, relative to the perchloric acid. Just to be sure, take a glass rod, dip this in the liquid and transfer some adhering liquid to a piece of pH paper. This paper should indicate a slightly alkaline solution. If the paper indicates an acidic solution, then add a few more drops of solution of hydrazine.

The resulting liquid (which has a slight excess of hydrazine) is transferred to a hour glass or petri dish and the glass or dish is put in a warm dry place (e.g. on a central heating radiator). Let the liquid evaporate for one day. After one day, a crystalline layer is formed in the petri dish. Scrap the solid from the glass and spread out the crystalline material again. Allow drying for another day. After this period, perfectly dry and non-hygroscopic crystals are obtained. The picture below shows the crystals, when added to a big test tube and photographed from above through the test tube.

The crystals look white in the picture, but in reality they are glass-like and transparent and perfectly colorless. A close-up of the crystals shows more details:

Igniting the solid material above a flame

The solid material can be put on a small spatula and kept above a flame. The solid first melts and sputters, giving rise to formation of beautiful fairy-like "glowing powder" and then suddenly the entire mass sets off with production of lots of glowing gas. No smoke remains. The reaction is not really explosive, but it goes fast and is quite spectacular.

A video of the reaction can be downloaded here. Download size is approximately 3 MByte.

Discussion of results

Hydrazine can be considered a diamine with two amino groups directly connected to each other. Both groups can accept a proton, but the second group does so with much more difficulty than the first group. This is because of the direct connection between the two -NH₂ groups. In this experiment, only one group is protonated:

      H₂NNH₂ + H⁺ → H₂NNH₃⁺

This ion easily forms salts with suitable anions. Commercial salts of this ion are available, such as the chloride and the sulfate.

With perchloric acid, the corresponding salt H₂NNH₃ClO₄ is formed. This salt forms colorless crystals which are not hygroscopic and which easily can be prepared by evaporating a solution of this.

The fairy powder effect is obtained due to boiling. A drop of the molten material is hanging under the spatula and this starts boiling. Little droplets of this boiling material decompose, giving bluish light and producing a noise which is somewhat between crackling and hissing.

The solid salt contains both the fuel and the oxidizer for the combustion. There is excess oxygen in the compound. All reaction products are gaseous and that explains the large fire ball and the lack of smoke. The orange color really is due to the glowing of the gas itself, it is not due to glowing particles like in a normal fire. For this reason, the orange glow is more 'ghost' like and no sharp flames are produced.

    H₂NNH₃ClO₄ → O₂ + HCl + 2H₂O + N₂

The reaction products are gaseous and colorless, hence no visible smoke nor visible gas can be perceived.

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