Question

Iodine is a (a) blue-black, (b) crystalline, and (c) solid. It (d) sublimes to a violet-colored gas and (e) reacts with aluminum and many other metals. Which of these five properties are physical, and which are chemical?

Short answer

Properties (a), (b), (c), and (d) are physical; (e) is chemical.

Step-by-step solution

Identify Physical Properties

Physical properties are characteristics that can be observed or measured without changing the substance's identity. These include color, state of matter, and appearance. In the provided descriptions: - "Blue-black" describes the color, which is a physical property. - "Crystalline" refers to the structure and appearance, another physical property. - "Solid" represents the state of matter, another physical property. - "Sublimes to a violet-colored gas" shows the ability to change state without changing the chemical structure, which is a physical property.

Identify Chemical Properties

Chemical properties describe a substance's ability to undergo changes that transform it into different substances. These properties often include reactivity with other substances. - "Reacts with aluminum and many other metals" indicates a chemical property since it involves a transformation of iodine into different compounds when it reacts with metals.

Key concepts

Substance Reactivity

Substance reactivity is an essential concept in chemistry, defining how a substance interacts with other materials. In the case of iodine, it reacts with aluminum and many other metals. This property is considered a chemical property because it involves a transformation into different compounds. Chemical properties are primarily concerned with how substances change their identity during reactions.
Substances vary widely in their reactivity. Factors influencing reactivity include:

• Reaction Conditions: Temperature, pressure, and the presence of catalysts can affect reactivity.
• Nature of Reactants: Some substances are naturally more reactive than others.
• Concentration: Higher concentrations can increase the rate of reaction.

Understanding reactivity helps chemists to predict how substances will behave in different environments and applications, such as in industrial processes or chemical synthesis.

State of Matter

The state of matter is a physical property that describes the form a substance takes based on its temperature and pressure conditions. Iodine is mentioned as being 'solid,' which is one of the classical states of matter. The three main states include solid, liquid, and gas, with others such as plasma and Bose-Einstein condensates being less common.
Key characteristics of different states:

• Solid: Defined shape and volume, with particles closely packed together.
• Liquid: Defined volume but no fixed shape, allowing it to flow and take the shape of its container.
• Gas: Neither defined shape nor volume, with particles spread apart and moving freely.

Physical changes in state do not alter the chemical structure of a substance. For example, when iodine sublimes from solid to gas, it retains its chemical identity.

Color and Appearance

Color and appearance are significant when identifying substances physically. Iodine, for example, is described as 'blue-black' and 'crystalline.' These descriptors are important because they help in recognizing the substance without altering its chemical nature.
Physical properties such as color and appearance can be observed with the senses and do not require altering the material's identity. They are stable constant properties at specified conditions:

• Color can be an essential identifier, though it's not always specific to a substance.
• Appearance involves shape, form, and structure, like the 'crystalline' form mentioned for iodine.

These properties are often used in everyday contexts, such as in quality control, identifying minerals, or artistic uses.

Sublimation

Sublimation is an intriguing physical process where a solid transitions directly into a gas without passing through the liquid phase. Iodine is a classic example, as it sublimates to form a violet-colored gas. This change of state is a physical property because it does not alter the chemical identity of iodine.
The process is important in various scientific and industrial applications, including:

• Purification Techniques: Sublimation can be used to purify substances.
• Manufacturing: Used in processes such as freeze-drying and the manufacture of dry ice.
• Analytical Chemistry: Helps in detecting and identifying volatile solids.

By understanding sublimation, scientists can manipulate conditions to separate or refine substances efficiently.