Recently we've seen several discussions of the internet on the use of liquid chalk and the possible effects it has on the Corona virus; will the alcohol stay on your hands long enough to break down the virus, is the alcohol concentration high enough etc.
The question I have, is on the addition of water to the mixture. Isn't the idea that chalk (magnesium-carbonate) is very hygroscopic, and it will drive water off your hands by a reaction of the pure magnesium-carbonate to one of its hydrated forms (di, tri or pentahydrate).
In my thought you would want to get a suspension of pure magnesium-carbonate in alcohol. Any addition of water to the mix will cause formation of a hydrate, and thereby lower the ability of the chalk to take up liquid from your hands. Of course, after initial evaporation of the alcohol, your hands will be bone dry regardless of the chalk in the mixture. But climbing with nice white coated hands, will the white layer do anything for you if its hydrated chalk, other than lower the friction.
So I've bought all the ingredients to make liquid chalk myself (isopropanol and chalk). Could probably make a litre of the stuff for the price of two small bottles liquid chalk in the shops.
Now I've done the experiment of mixing chalk with 99.7% isopropanol, and a second mixture using 70% isopropanol and water.
- adding water immediately thickens the mixture
- the thicker mixture smears better, but the mixture with pure alcohol feels nicer on the skin
- after the alcohol evaporated I sprinkled a few drops of water on my white coated hands, and I have the idea that the pure alcohol mixtures leaves a layer that absorbs more water
I then tried to do some proper science, by mixing equal amounts (10 grams of chalk) and leaving the mixture to dry on a very precise laboratory scale. The scale should be accurate enough to measure the differences between pure and hydrated magnesium-carbonate. And then the battery died, and I had no spares
Any chemists around that can contribute?