Have you ever seen a “chicken of time”? They are those bibelots in the shape of a small rooster that, depending on weather conditions, can be blue or pink. If this decoration is pink, it is likely that the weather will be rainy and cold. But if it's blue, the day will likely remain warm with no rain forecast.
It's true that forecasting the weather is something much more complex that involves several variables. Currently, meteorology uses many equipment that study the properties of the atmosphere to be able to predict whether it will rain or not, such as barometers (measure air pressure), thermometers (measure air temperature) and hygrometers (measure moisture).
Thus, the time twigs cannot actually determine the weather variations that will occur in the future; rather, they just serve to record current weather variations. But how does he do it?
Well, this knickknack has an aqueous solution of cobalt II chloride on its surface, which establishes the following chemical balance:
[CoCℓ4]2-(here) + 6 H2O(ℓ)↔ [Co(H2O)6]2+(here)+ 4 Cℓ1-(here)
The ion [CoCl4]2-(here) has a blue color, and its coordination number (amount of anions that surround the cation in the crystalline arrangement) is 4. The ion [Co (H2O)6]2+ it is pink and its coordination number is 6.
According to Le Chatelier's Principle, this balance can be shifted to the right, leaving the salt pink or to the left, turning the color blue. There are two factors in the case of "chickens of time" that can shift the ionic balance of this reaction, which are:
1- Degree of hydration:
When the weather is dry, the salt becomes anhydrous, since the amount of water in the atmosphere is low, the balance shifts towards the inverse reaction, formation of water and ion [CoCl4]2-. Thus, the salt turns blue, indicating that the weather is dry, with no forecast of rain.
However, when the air is humid, the reaction is shifted towards the direct reaction, forming the hydrated salt ([Co (H2O)6]2+), which is pink. Therefore, when the rooster turns pink, it indicates wet weather with the possibility of rain.
2- Temperature variation:
On hot days (high temperature) the equilibrium of the reaction shifts towards the heat-absorbing reaction (endothermic), which, in this case, is the opposite. The rooster then turns blue, confirming that the weather will be hot.
On cold days, on the other hand, the low temperature causes the equilibrium to be shifted towards the reaction that releases heat (exothermic), which, in the example considered here, is the right one. In this case, the weather cock turns pink, confirming that it will be a cold day.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/como-funciona-galinho-tempo.htm
