Question

why is solid co2 known as ice

Answer 1

Solid form of CO2 is called dry ice. It is called so because CO2 gas on solidification it resembles ice. Unlike normal ice (water ice) does not melt into a liquid but changes directly into CO2 gas, a phenomenon known as sublimation. It changes into gaseous state at and above -78.5 degree Celsius. This temperature is much lower than water; hence it is much colder than water ice. It is also denser than water.

It is mainly used as a cooling agent because it has temperature lower than that of water ice. It is used for preserving frozen foods; ice cream etc. where mechanical cooling is unavailable.