Problem 17 - Chemistry: The Central Science

Question

In the process of attempting to characterize a substance, a chemist makes the following observations: The substance is a silvery white, lustrous metal. It melts at 649 \({ }^{\circ} \mathrm{C}\) and boils at \(1105{ }^{\circ} \mathrm{C}\) Its density at \(20{ }^{\circ} \mathrm{C}\) is \(1.738 \mathrm{~g} / \mathrm{cm}^{3} .\) The substance burns in air, producing an intense white light. It reacts with chlorine to give a brittle white solid. The substance can be pounded into thin sheets or drawn into wires. It is a good conductor of electricity. Which of these characteristics are physical properties, and which are chemical properties?

Step-by-Step Solution

Answer

The physical properties of the substance are its silvery-white, lustrous appearance, melting point (649°C), boiling point (1105°C), density (1.738 g/cm³ at 20°C), malleability (can be pounded into thin sheets or drawn into wires), and conductivity (good conductor of electricity). The chemical properties are its ability to burn in air, producing an intense white light (reaction with oxygen), and its reaction with chlorine to give a brittle white solid.

Step 1: List the observations

Here are the given observations about the substance: 1. Silvery white, lustrous metal. 2. Melting point is 649°C. 3. Boiling point is 1105°C. 4. Density at 20°C is 1.738 g/cm³. 5. Burns in air, producing an intense white light. 6. Reacts with chlorine to give a brittle white solid. 7. Can be pounded into thin sheets or drawn into wires. 8. Good conductor of electricity.

Step 2: Identify physical properties

Physical properties are characteristics that can be observed or measured without changing the composition of the substance. In the given observations, the following are physical properties: 1. Silvery white, lustrous metal (appearance). 2. Melting point (649°C). 3. Boiling point (1105°C). 4. Density (1.738 g/cm³ at 20°C). 7. Malleability (can be pounded into thin sheets or drawn into wires). 8. Conductivity (good conductor of electricity).

Step 3: Identify chemical properties

Chemical properties describe how a substance reacts with other substances or changes its composition. In the given observations, the following are chemical properties: 5. Burns in air, producing an intense white light (reacts with oxygen). 6. Reacts with chlorine to give a brittle white solid (reacts with chlorine). In conclusion, the observations of the substance can be divided into physical properties (appearance, melting point, boiling point, density, malleability, and conductivity) and chemical properties (reaction with oxygen and reaction with chlorine).

Key Concepts

Physical Properties of Matter

Understanding the physical properties of matter is crucial for students as these properties can be observed and measured without changing the substance's composition. Physical properties include characteristics like color, melting point, boiling point, density, malleability, and electrical conductivity. For instance, when a substance is described as 'silvery white and lustrous,' it refers to its color and sheen, which are surface properties.

Another physical property is the state of matter, which can be solid, liquid, or gas at room temperature. The melting point, like the 649°C for the substance in our exercise, is the temperature at which a solid becomes a liquid. Similarly, a boiling point is where a liquid turns into gas – for our substance, that's 1105°C. The density, another key physical property, is defined as mass per unit volume and affects how substances interact with one another in a mixture. Lastly, malleability and conductivity tell us how a substance can be deformed or how well it conducts electricity respectively. These properties are all essential when identifying a substance and predicting how it will behave in different scenarios.

Chemical Properties of Matter

Contrary to physical properties, chemical properties of matter describe a substance's potential to undergo changes that alter its composition. These are not as readily observable as physical properties and typically involve a chemical reaction. For example, a chemical property of a substance might be its reactivity with oxygen, like how the substance in the exercise burns in air to produce an intense white light.

Another aspect is its behavior with other chemicals, like how the substance reacts with chlorine to form a brittle white solid. These chemical reactions result in the formation of a new substance with different properties from those of the original substance. Understanding chemical properties is instrumental in predicting how a substance will behave in a chemical reaction, which is essential for safety and in applications like pharmaceuticals, materials science, and environmental science. It's important for students to grasp that while physical changes can be reverted, chemical changes typically result in new materials that cannot easily be changed back.

Conductivity in Metals

The conductivity of metals is a major physical property that limns their ability to transport heat and electricity. Metals are known for their high conductivity, which is why they are widely used in electrical wiring and electronic components. The free electrons in metals, also known as conduction electrons, are responsible for their high conductivity. When a voltage is applied across a metal, these free electrons move towards the positive side, creating an electric current.

Metal conductivity can change with temperature, with most metals becoming less conductive as the temperature rises, due to increased electron scattering. The metal in our exercise is noted for being a 'good conductor of electricity,' indicating a significant presence of free electrons that can move with ease, which accounts for its effectiveness in conducting electric current. This property is fundamental in applications where efficient energy transfer is desired.

Malleability of Metals

The malleability of metals is a fascinating physical property that allows them to be hammered or rolled into thin sheets without breaking. This malleability is due to the metallic bonding, where metal atoms share a sea of electrons that can slide past each other under stress without fracturing the material. The exercise mentions the substance can be 'pounded into thin sheets or drawn into wires,' exemplifying its malleability.

Metals like gold, silver, and the one described in our exercise are malleable, making them invaluable in industries like manufacturing and jewelry making. A thorough understanding of a metal’s malleability can assist in determining its applications. For example, metals that are highly malleable are often used in areas where they need to be shaped into complex forms, such as in aerospace, automotive, and consumer electronics.