Question

Identify each property as chemical or physical. (Chapter 3) a. The element mercury has a high density. b. Solid carbon dioxide sublimes at room temperature. c. Zinc oxidizes when exposed to air. d. Sucrose is a white crystalline solid.

Short answer

a. Physical property (high density) b. Physical property (sublimation) c. Chemical property (oxidation) d. Physical properties (color and physical state)

Step-by-step solution

a. High density of mercury

Density is a measure of mass per unit volume of a substance and does not involve any change in the chemical composition of the substance. Therefore, the high density of mercury is a physical property.

b. Sublimation of solid carbon dioxide at room temperature

Sublimation is the process in which a substance changes its state from solid to gas without passing through the liquid stage. There is no change in the chemical composition of carbon dioxide during this process, only a phase change. Thus, the sublimation of solid carbon dioxide at room temperature is a physical property.

c. Oxidation of zinc when exposed to air

Oxidation is a chemical process where a substance loses electrons and reacts with oxygen, causing a change in its chemical composition. When zinc is exposed to air, it reacts with oxygen to form a new substance, zinc oxide. Therefore, the oxidation of zinc when exposed to air is a chemical property.

d. Sucrose being a white crystalline solid

The color (white) and the physical state (crystalline solid) of sucrose describe its appearance and do not involve any change in its chemical composition. These are both examples of physical properties.

Key concepts

Chemical Properties

Chemical properties are characteristics of a substance that become evident during a chemical reaction. They relate to a substance's ability to undergo changes that transform it into different substances.
A key aspect of chemical properties is that they involve a change in the identity of the material you start with. For example:

• Flammability - A material's ability to catch fire and burn.
• Reactivity with acids - How a substance might react when it comes into contact with an acid.
• Oxidation - The process where a material reacts with oxygen, which could result in rusting or tarnishing.

Understanding chemical properties is crucial in fields such as chemistry and materials science because it helps predict how substances will behave in different environments.

Physical Properties

Physical properties are characteristics of a substance that can be observed or measured without changing the substance's chemical identity. These properties include features like color, smell, freezing/melting point, and density.
Physical properties can be either extensive or intensive:

• Extensive properties depend on the amount of matter, such as mass and volume.
• Intensive properties do not depend on the amount of matter, such as density and boiling point.

These properties are vital for identifying materials and determining their applications in various industries. For instance, knowing the melting point of a metal is essential in metallurgy to ensure the metal can withstand certain temperatures without changing state.

Density

Density is an intensive physical property defined as the mass per unit volume of a substance. It is usually expressed in units such as grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³).
This property provides insights into how closely packed or concentrated the particles within a substance are. High-density materials have tightly packed particles, whereas low-density materials have more spaced-out particles.
Density is crucial in identifying substances and can be used to predict if an object will float or sink in a fluid. For example, mercury, known for its high density, is used in barometers and thermometers. Calculating density involves the formula:\[\text{Density} = \frac{\text{Mass}}{\text{Volume}}\]
This straightforward calculation is key to many practical fields, including physics and engineering.

Phase Change

Phase changes are transitions between different states of matter: solid, liquid, gas, and plasma. Common examples include melting, freezing, condensation, and sublimation.
These changes occur due to variations in temperature and pressure, and don't involve a change in the chemical composition of the substance. During sublimation, for example, a solid like dry ice transforms directly into gas without becoming liquid.
Phase changes are crucial in understanding natural phenomena and are applied in various fields such as meteorology, cooking, and materials science. They are often accompanied by energy transfer, such as heat absorption or release. Thus, knowing about phase changes helps in controlling and utilizing heat energy effectively in industrial processes.

Oxidation

Oxidation is a chemical process involving the loss of electrons from a substance, which often leads to the substance reacting with oxygen. This can result in the formation of oxides, such as when iron forms rust or zinc forms zinc oxide.
Oxidation is a critical concept in chemistry, particularly in the study of redox reactions, where oxidation and reduction occur simultaneously. Everyday examples of oxidation include:

• The browning of fruits when exposed to air.
• Certain reactions in metabolism that release energy from food.
• Corrosion of metals.

Understanding oxidation helps in developing methods to prevent damage caused by it, such as using coatings to protect metals from rusting. It's also essential in biological systems, where controlled oxidation processes are necessary for life-sustaining reactions.