Problem 43 - Chemistry A Molecular Approach

Question

Classify each of the listed properties of isopropyl alcohol (also known as rubbing alcohol) as physical or chemical. MISSED THIS? Read Section 1.4 a. colorless b. flammable c. liquid at room temperature d. density \(=0.79 \mathrm{~g} / \mathrm{mL}\) e. mixes with water

Step-by-Step Solution

Answer

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

Step 1: Identify Physical Properties

Physical properties can be observed or measured without changing the identity of the substance. They include attributes such as color, state of matter (solid, liquid or gas at room temperature), density, melting point, boiling point, and solubility.

Step 2: Classify Property 'a'

'Colorless' is a physical property because it describes the appearance of isopropyl alcohol without changing its chemical makeup.

Step 3: Classify Property 'b'

'Flammable' is a chemical property because it describes the substance's ability to undergo a chemical change; in this case, the ability to burn in the presence of oxygen.

Step 4: Classify Property 'c'

'Liquid at room temperature' is a physical property because it describes the state of the substance under normal conditions and does not involve changing into another substance.

Step 5: Classify Property 'd'

A density of '0.79 g/mL' is a physical property as it is a measure of how much mass there is in a given volume of the substance.

Step 6: Classify Property 'e'

'Mixes with water' is a physical property because it describes how isopropyl alcohol behaves in the presence of water, indicating it is miscible, without undergoing a chemical change.

Key Concepts

Chemical Properties

Chemical properties of a substance provide insights into the potential ways that material can undergo a chemical change to form new substances. These properties can only be observed during a chemical reaction and are associated with the ability of a substance to change its chemical structure.

Examples of chemical properties include reactivity with other chemicals, flammability, acidity, and the ability to rust or tarnish. For instance, consider the flammability of isopropyl alcohol (rubbing alcohol). This chemical property implies that when isopropyl alcohol is introduced to an ignition source within the presence of oxygen, it will ignite and burn. The process transforms the alcohol into different substances, such as carbon dioxide and water, which is why flammability is a chemical property.

Physical Properties

Physical properties are characteristics that can be observed or measured without altering the composition or identity of a substance. These properties are the most apparent attributes we identify with our senses or with the help of instruments.

An excellent introductory list of physical properties includes color, phase of matter (such as solid, liquid, or gas), density, melting point, boiling point, and solubility. For example, isopropyl alcohol being colorless and liquid at room temperature are physical properties. These traits can be identified without triggering a chemical reaction or changing the chemical makeup of the alcohol. The same goes for its density at 0.79 g/mL, which relates the substance's mass to its volume.

Isopropyl Alcohol Characteristics

Isopropyl alcohol, commonly known as rubbing alcohol, exhibits several distinctive physical and chemical properties. As a colorless liquid at room temperature, it has a physical property similar to that of water, which makes it easy to identify visually.

Moreover, isopropyl alcohol is notable for its miscibility with water, meaning they can be mixed in any proportion without separating, which reflects on the nature of its intermolecular forces. Physically, it has a lower density than water, precisely 0.79 g/mL, and this property is often used to determine the quality or concentration of the alcohol. Chemically, its ability to be flammable is a critical property regarding handling and storage as it can easily be a source of fire.

Property Classification

Property classification is an essential practice in chemistry, as it helps to distinguish between the intrinsic characteristics of substances. It allows scientists and students alike to organize and understand materials based on observable and measurable traits.

Classifying a property as either physical or chemical depends on whether the observation or measurement involves changing the substance's chemical identity. Therefore, if the property can be noted without changing the substance itself, such as its color or melting point, it is physical. In contrast, if the property involves the substance's interaction and transformation into a new material, like reactivity or flammability, it is chemical. By understanding these classifications, one can predict how a substance will behave in different conditions and how it can be used or should be handled.