Question

Classify each as a physical property or a chemical property. a. Aluminum has a silvery color. b. Gold has a density of 19 \(g/cm^{3}\) . c. Sodium ignites when dropped in water. d. Water boils at \(100^{\circ} C\) e. Silver tarnishes. f. Mercury is a liquid at room temperature.

Short answer

a. Physical property b. Physical property c. Chemical property d. Physical property e. Chemical property f. Physical property

Step-by-step solution

a. Aluminum has a silvery color.

This is describing Aluminum's appearance, which is a physical property since it doesn't involve any chemical reactions.

b. Gold has a density of 19 \(g/cm^{3}\).

Density is related to the mass and volume of a substance, making it a physical property.

c. Sodium ignites when dropped in water.

Ignition involves Sodium reacting with water to create a new substance, making it a chemical property.

d. Water boils at \(100^{\circ} C\).

Boiling is a phase transition, which makes it a physical property as no chemical reaction is occurring.

e. Silver tarnishes.

Tarnishing involves Silver reacting with sulfur or other elements in the air to form a new compound; therefore, it is a chemical property.

f. Mercury is a liquid at room temperature.

This statement is describing the phase of Mercury, making it a physical property.

Key concepts

Physical Property

A physical property is an attribute or characteristic of a substance that we can observe or measure without altering the substance itself. For instance, the color, density, and melting or boiling points are all physical properties. These properties help to describe the state of the material and how it looks or feels.

When you hear that aluminum has a silvery color or that gold has a density of 19 \(g/cm^{3}\), these are typical examples of physical properties. They give us an idea about the material's appearance and mass characteristics without hinting at any chemical changes. Similarly, the fact that mercury is a liquid at room temperature tells us about its state of matter without undergoing any chemical reaction.

Chemical Property

Chemical properties define how a substance interacts with other substances, which involves a chemical change. These properties indicate the potential of a material to undergo certain chemical reactions, resulting in a change in its chemical structure and making new substances.

Sodium igniting when dropped in water is a classic example of a chemical property. This scenario showcases sodium's tendency to react violently with water, producing a new chemical substance. Another example is silver tarnishing. This involves a slow reaction with sulfur compounds in the air, leading to a dull, blackish layer of silver sulfide. Both incidents illustrate how chemical properties revolve around reactivity and the formation of new materials.

Phase Transition

Phase transition refers to the change from one state of matter to another. Common transitions include solid to liquid, liquid to gas, and vice versa. Importantly, phase transitions are physical changes because they do not alter the chemical identity of the substance.

When water boils at \(100^{\circ}C\), it undergoes a liquid to gas phase transition. This process does not involve a chemical reaction; instead, it is a physical change where water molecules move into a gaseous state due to increased temperature. The overriding factor remains: the water's chemical structure remains intact.

Reaction with Water

A reaction with water is often a telltale sign of a chemical property. This involves the interaction between a substance and water, resulting in a new chemical composition.

An excellent example of this is sodium. When sodium is introduced to water, it reacts vigorously, often igniting, and forms sodium hydroxide and hydrogen gas. This highlights sodium's chemical property, as a chemical reaction causes the transformation into new compounds.

• This reinforces the principle that chemical reactions involve substance transformation.
• Different substances may react variably with water, indicating their unique chemical properties.

By understanding these reactions, we gain deeper insight into the behaviors and characteristics of substances when exposed to different environments.