Professor Emeritus Rein Munter. Photo by TalTech
Readers’ questions will be answered by Rein Munter, professor emeritus of the Tallinn University of Technology, chemical scientist.
How do ice and snow form and what is the most common shape of a snowflake?
Water in a solid state is called ice. Ice has a crystalline structure and has voids in its crystal lattice, which is why ice is less dense than liquid water. Snow is nothing more than water frozen in the atmosphere into ice crystals. Weather researchers have known for more than 70 years that ice crystals grow in clouds at certain temperature ranges.
At -2°C thin plaques form. When the temperature drops to -5 degrees, needles and columnar crystals form. At a temperature of -15 degrees, ultra-thin plates form, when the temperature drops below -30°C columns and pillars form again. So far, no one has been able to reasonably explain why snow crystals of completely different shapes form even with a temperature change of just a few degrees.
The most common shape of the snowflake (hexagonal) comes from the structure of the ice crystal. Snow, like diamond or table salt, is a mineral, it has a defined crystalline structure. Water molecules form hydrogen bonds with other water molecules in ice, the internal angles of the polygons formed are 60 degrees. Even during the formation of ice, the structure with the greatest stability under certain environmental conditions is formed, i.e. the hexagonal ice crystals in the Earth’s lower atmosphere.
When does salt water freeze?
Water freezes at 0 oC. The presence of salt (3.5%) lowers the freezing point by ~2 °C and at the same time lowers the temperature at which the density of water reaches its maximum to the freezing point. The surface of salt water begins to freeze at a temperature of -1.9 °C (water with a salinity of 3.5%), however the ice that forms is almost free of salt and the density is comparable to that of ‘fresh water. The density of water in normal conditions is approximately 1 g/cm3, but it depends directly on the temperature. At around 4°C water reaches its maximum density. The density of water also depends on the concentration of dissolved substances.
Why are frozen water pipes bursting just as the climate warms?
When it freezes, the ice grows from the wall to the center, and the elasticity of the tube can resist the ice. Ice does not melt immediately when it heats up. Instead, it begins to expand like any normal solid body and forces the tube to rupture at the final breaking point.
2023-12-19 13:03:56
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