Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
ethylene diamine : NH2 CH2 CH2 NH2
iodic acid : HIO3
Class:
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elem=C,I
acid/base
precipitation
Summary:
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Ethylene diamine (NH2CH2CH2NH2) and iodic acid form a moderately soluble salt.
In the dry state, this salt is fairly stable. Only when it is heated strongly,
it decomposes with a soft puff, giving a yellow/brown smoke and a bad smell.
Description:
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Mix approximately 0.3 ml of ethylene diamine with 0.5 ml of water. To this mix
add a solution of iodic acid: As soon as the solution of iodic acid touches the
liquid, a white solid is formed. This solid, however, quickly redissolves
again.
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Add a few drops of the mix of ethylene diamine to a solution of iodic acid: A
white precipitate is formed.
Add a few more drops of the mix of ethylene diamine: The white solid
redissolves again.
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Mix all of the iodic acid and ethylene diamine with each other: A clear
solution is obtained.
Pour this solution in a petridish and put this in a warm and dry place (appr.
40 C): Slowly, a white crystalline solid (needle-like crystals) is formed while
the water (and probably excess ethylene diamine as well) evaporates. After 24
hours, a dry solid obtained. This solid appears to be slightly hygroscopic.
Take a small spatula full of the solid and keep it in a flame: The solid, which
is in the flame decomposes with a soft puff/hiss and some yellow/brown smoke,
together with some purple iodine vapor is produced. The decomposition stops
when the solid is taken out of the flame, it is not self-sustaining.
Take another spatula of this solid and add it to a few drops of 30%
hydrochloric acid: The solid quickly dissolves while fizzling and the liquid
becomes bright yellow and clear. A strong smell of chlorine can be observed.
There also is some white smoke (most likely this is due to the presence of some
free ethylene diamine in the solid).