Question

A dry ice piece is composed of: (a) Solid \(\mathrm{C}_{6} \mathrm{H}_{6}\) (b) Solid \(\mathrm{SO}_{2}\) (c) Solid \(\mathrm{CO}_{2}\) (d) Solid He

Short answer

(c) Solid \( \mathrm{CO}_{2} \) is dry ice.

Step-by-step solution

Identify the Components of Dry Ice

Dry ice is commonly referred to as solid carbon dioxide. It sublimates from a solid to a gas at room temperature and pressure. Among the given options, identify which one represents solid carbon dioxide.

Match Dry Ice to Chemical Formula

Among the chemical formulas provided, \( \mathrm{CO}_{2} \) represents carbon dioxide. Thus, solid \( \mathrm{CO}_{2} \) matches the description of dry ice.

Key concepts

Solid Carbon Dioxide

Solid carbon dioxide is commonly known as dry ice. Unlike regular ice that is made from water, dry ice is formed from carbon dioxide gas. When exposed to very low temperatures, carbon dioxide gas transitions into a solid state forming dry ice.

This solid form of carbon dioxide is incredibly cold, with a temperature of about -78.5 degrees Celsius or -109.3 degrees Fahrenheit. Due to this unique characteristic, it is often used for cooling purposes, especially when a colder temperature is required than what water ice can provide.

Dry ice is commonly used in shipping perishable items, creating fog effects for entertainment, and even in scientific experiments.

Sublimation

Sublimation is a fascinating process where a substance changes from a solid state directly into a gas, bypassing the liquid phase. This is exactly what happens with dry ice.

The reason dry ice sublimates instead of melting is due to its chemical structure and atmospheric pressure conditions. When exposed to room temperature, solid carbon dioxide absorbs heat energy and directly turns into carbon dioxide gas. This transition happens without wetness because it skips the liquid phase altogether.

This property is particularly useful when a clean, residue-free cooling agent is desired. Hence, dry ice is often used in situations where keeping things dry is paramount.

Chemical Formulas

Chemical formulas are a concise way of representing chemical substances using symbols for their elements. For example, the formula for water is \( \mathrm{H}_2\mathrm{O} \), which indicates it contains two hydrogen atoms and one oxygen atom.

In the context of dry ice, the chemical formula \( \mathrm{CO}_{2} \) signifies carbon dioxide. This formula tells us that each molecule consists of one carbon atom and two oxygen atoms. Recognizing chemical formulas is essential for identifying substances based on their elemental composition.

For students, understanding and becoming familiar with chemical formulas will greatly aid in recognizing and predicting the behavior of different chemical substances.

Identification of Substances

Identifying substances is a critical skill in chemistry that involves recognizing the unique properties and formulas of materials. To identify dry ice, look for its solid state and characteristic sublimation process.

In exercises where multiple options are presented, being able to identify the correct chemical formula (such as \( \mathrm{CO}_{2} \) for dry ice) is important. Noticing the physical characteristics, such as its extreme coldness and sublimating nature, further aids in confirming the identity.

Moreover, using other identifiers, such as weight, color, and interaction with other substances, can help confirm the identity of a substance, though dry ice is mostly identified through its unique thermal and chemical behavior.