Question

State whether the following properties are physical or chemical. (a) A piece of sliced apple turns brown. (b) A slab of marble feels cool to the touch. (c) A sapphire is blue. (d) A clay pot fired in a kiln becomes hard and covered by a glaze.

Short answer

(a) Chemical property, (b) Physical property, (c) Physical property, (d) Chemical property.

Step-by-step solution

Define Physical and Chemical Properties

Physical properties are characteristics that can be observed or measured without changing the identity of the substance. Examples include color, odor, texture, state of matter, boiling and melting point, and hardness. Chemical properties describe a substance's ability to undergo a chemical change, turning it into a different substance. Examples are reactivity, flammability, and the ability to rust or oxidize.

Identify Property (a)

When an apple is cut or bruised, it turns brown due to a chemical reaction between enzymes in the apple and oxygen in the air. This change affects the composition of the apple, thus it's a chemical property.

Identify Property (b)

When a slab of marble feels cool to the touch, that is a physical property. This sensation is related to the marble's ability to conduct heat, which does not involve a change in the substance's composition.

Identify Property (c)

The color of a sapphire is a physical property. The color is observable without interacting with the substance and changing its composition.

Identify Property (d)

When a clay pot is fired in a kiln and becomes hard and covered by a glaze, the clay undergoes a chemical change. This process alters the chemical structure of the clay, making it a chemical property.

Key concepts

Chemical Reactions

A chemical reaction involves a process that changes the molecular structure of a substance. It occurs when substances interact to form new products. These interactions often result in observable changes, such as color shift, gas production, or temperature change. In the context of the exercise, when a sliced apple turns brown, this results from a chemical reaction between enzymes and oxygen. Similarly, firing a clay pot in a kiln involves chemical reactions that change its composition. Understanding chemical reactions helps us predict how substances will behave under various conditions, informing fields like medicine, industry, and everyday life.

Physical Change

A physical change refers to alterations affecting the form of a substance, without changing its chemical identity. Common examples include melting, freezing, and the transition from one state of matter to another, such as water turning to steam. Notably, cooling a marble slab doesn't alter its molecular structure; it simply feels cool due to its thermal properties, a classic physical change. Similarly, the color of a sapphire is an intrinsic characteristic not altered chemically. These changes are typically reversible, allowing substances to return to their original state.

Observing Properties

Observing properties of substances helps us determine whether a change is physical or chemical. Characteristics like color, temperature, and texture can offer clues. For instance:

• Color: While a sapphire is blue as its inherent trait without chemical alteration, a browning apple signifies a chemical change due to oxidation.
• Temperature: Marble feels cool without a chemical transformation.

Observations are crucial for scientists and students, allowing them to explore substances' behaviors and reactions with simple senses or instruments, aiding in assessments of material properties.

Substance Composition

Substance composition refers to the specific makeup of a material, defining its chemical structure and properties. Changes in composition often signal chemical changes, like the hardening of clay in a kiln. These modifications alter the molecular structure, leading to new substances with different properties. Conversely, physical changes, such as the marble slab's thermal response, maintain the inherent composition. Understanding substance composition is vital for identifying substances, predicting their interactions, and applying this knowledge in real-world scenarios ranging from material science to environmental studies.