Preparation of Silver Tetraiodomercurate(II) for a demonstration.

Silver Tetraiodomercurate(II) is a quite special compound, since it’s thermochromic. It changes color from yellow to orange/red when heated:

Silver Tetraiodomercurate (Ag2HgI4) is yellow at room temperature, but when it’s heated above 50 °C, it turns orange. Since the color change is reversible, when it is cooled back to room temperature, the color changes back to its original color.

The compound was prepared from mercury(II)-iodide (that red powder on the first picture) and some potassium iodide with a little silver nitrate. The silver nitrate was added to the solution of potassium tetraiodomercurate (K2HgI4,   what was previously prepared from mercury-iodide and potassium iodide). The addition of the silver salt caused the immediate precipitation of the yellow colored silver tetraiodomercurate (as seen on the gif).

What happened? This:

HgI2 + 2 KI + 2 AgNO3 –> Ag2HgI4 + 2 KNO3

Good move, Old-Timey Ad Lady!

4 Tiny Historical Changes That Made Modern Life Possible

#4. You Have a Higher IQ Because of Chemicals Added to Salt

For most of history, humankind has been tormented by goiter, which is one of those rare words that is exactly as unfortunate as the thing it describes. Basically, goiter is a condition that makes you look like you swallowed a plastic shopping bag full of golf balls. … It wasn’t until the 1920s that a doctor called David Murray Cowie heard about how landlocked Switzerland had vitalized their neck modeling industry by adding sodium iodide to the nation’s table salt. Cowie convinced some of America’s biggest salt manufacturers to follow the Swiss plan and dose America’s salt right up. At the time, iodine fans were focused on preventing deficiency and wiping out those nasty neck lumps. But then, in what was the exact opposite of every science fiction plot ever, this newfangled chemical in our food came with an unexpected side effect … it made people smarter. In areas where iodine deficiency was formerly the norm, iodizing table salt increased people’s IQ an average of 15 points.

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Lifesaving bindi is a wearable iodine supplement

In rural India, iodine deficiency contributes to the medical problems of millions of women each year. Despite the country supplementing its salt with the vital nutrient, there are still an estimated 350 million Indians who don’t get enough in their diet. That deficiency can cause complications during pregnancy, preventable brain damage and more. Now, an initiative called Life Saving Dot is helping underprivileged women to get their required iodine dosage, via enhanced, nutritious bindis. READ MORE…


Because yesterday the whole amount of my compound decomposed to give a black tar, I have to prepare it again. One easy method for the production of iodinated compounds from bromine or chlorine substituted alkanes is the Finkelstein reaction.

What is the Finkelstein reaction? Finkelstein Reaction is a HalEx (Halogen Exchange) reaction what lets to change a bromine or chlorine to an iodine atom on an organic molecule. The trick is, that sodium iodide is well soluble in acetone (first pics), while the sodium chloride and sodium bromide is nearly insoluble. What happens is simple: R-X + NaI = R-I + NaX. The reaction is based on an equilibrium what only goes one direction, since the NaX gets removed from the reaction since it precipitates (third pics).  On the second pics the pressure tube was heated during the reaction what causes the product to decompose a bit and this is the reason of the yellow color. Luckily there is  alot stabilizer in the reaction mixture so at the end (third pics) only the precipitated sodium chloride is seen in the tube.