Question

Solid carbon dioxide is known as dry ice because:
a. It melts at 0 degree Celsius
b. Its boiling point is more than 199 degree Celsius
c. It evaporates at -78 degree Celsius without melting
d. None of the above

Answer 1

Hint: Solid carbon dioxide is a molecular solid, which undergoes sublimation and provides a cooling effect. As the name suggests, solid carbon dioxide is made by directly converting the carbon dioxide gas to solid.

Complete step by step answer:
As the name suggests, solid carbon dioxide is the solidified form of gaseous carbon dioxide, which appears as a dense, snow-like substance that sublimes at -78 degree Celsius. It is known as dry ice for the same reason.
Sublimation is the process of conversion of state of matter from solid to gas and vice-versa, without converting to liquid. The phase transition takes place through processes such as melting, freezing and evaporation.
Therefore, the answer is – option (c) – Solid carbon dioxide is known as dry because it evaporates at -78 degree Celsius without melting.

Additional Information:
Dry ice is very widely used as a refrigerant, especially in shipping of perishable food products. It is also used in packing frozen items.

Note: Solid carbon dioxide or dry ice is manufactured by spontaneous cooling of carbon dioxide at a temperature of around – 57 degree Celsius or lower under high pressure. After this, it is allowed to suddenly expand to atmospheric pressure. Now, the carbon dioxide freezes to a dense solid.