Problem 19 - Chemistry The Central Science

Question

In the process of attempting to characterize a substance, chemist makes the following observations: The substance i a silvery white, lustrous metal. It melts at \(649^{\circ} \mathrm{C}\) and boils a \(1105^{\circ} \mathrm{C} .\) 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 of \(649^{\circ}\mathrm{C}\), boiling point of \(1105^{\circ}\mathrm{C}\), density at \(20^{\circ}\mathrm{C}\) (1.738 g/cm³), malleability, ductility, and electrical conductivity. The chemical properties are its reaction with oxygen (burns in air, producing intense white light) and reaction with chlorine (forming a brittle white solid).

Step 1: List the observations

1. Silvery-white, lustrous metal 2. Melts at 649°C and boils at 1105°C 3. Density at 20°C is 1.738 g/cm³ 4. Burns in air, producing intense white light 5. Reacts with chlorine to give a brittle white solid 6. Can be pounded into thin sheets or drawn into wires 7. Good conductor of electricity

Step 2: Identify physical properties

Physical properties can be observed without changing the chemical identity of the substance. From the given observations, the following are physical properties: 1. Silvery-white, lustrous metal (appearance) 2. Melts at 649°C and boils at 1105°C (melting and boiling points) 3. Density at 20°C is 1.738 g/cm³ (density) 6. Can be pounded into thin sheets or drawn into wires (malleability and ductility) 7. Good conductor of electricity (electrical conductivity)

Step 3: Identify chemical properties

Chemical properties describe how a substance reacts with other substances, and they can only be observed during a chemical reaction. From the given observations, the following are chemical properties: 4. Burns in air, producing intense white light (reaction with oxygen) 5. Reacts with chlorine to give a brittle white solid (reaction with chlorine) Now we have identified the physical and chemical properties based on the chemist's observations.

Key Concepts

Chemical Reactivity

Chemical reactivity is a term that refers to the ability of a substance to undergo chemical changes. This involves the substance's tendency to engage in chemical reactions with other substances, such as acids, bases, or oxidizing agents. The observations from the exercise that link to chemical reactivity would be the substance burning in air to produce an intense white light and its reaction with chlorine to form a brittle white solid. Burning in air indicates a reaction with oxygen, which demonstrates the substance's reactivity towards oxidizing environments.

Furthermore, the formation of a brittle white solid upon reacting with chlorine shows the substance's specific reactivity to halogens. These observations are crucial because they reveal how the substance interacts at the molecular level and can significantly influence the way the substance can be used. For instance, a high reactivity with oxygen might suggest that the substance needs to be stored and handled in an inert atmosphere to prevent unwanted reactions.

Material Properties

Material properties are the characteristics of a substance that become evident during the testing of its reaction to external influences, such as force, temperature, and other environmental factors. These properties are essential for determining the applications and limitations of a material. In the exercise, physical properties such as the appearance of the substance being a silvery-white, lustrous metal, its melting and boiling points, density, and its ability to be shaped into thin sheets or wires, represent critical material properties.

Each property potentially affects its practical use. For example, a high melting and boiling point would suggest suitability for high-temperature applications, whereas malleability and ductility dictate its ability to be fashioned into various shapes and forms without breaking. Understanding these material properties is paramount for engineers and designers when selecting materials for different purposes.

Conductivity in Chemistry

Conductivity in chemistry refers to a material's ability to allow the flow of electric charge or heat. This physical property is significant as it dictates the potential applications of a material in electronic and thermal devices. In the provided exercise, the substance is described as a good conductor of electricity, indicating that it allows electrical current to pass through with minimal resistance.

Good conductivity is essential in materials used for wiring, electronic components, and circuitry. The ability to conduct electricity relates to the structure and bonding of elements and compounds. Materials with free moving electrons - often metals - tend to exhibit high electrical conductivity. In teaching this concept, drawing parallels between the movement of electrons and the flow of water in pipes can be a helpful illustration for students to visualize how conductivity works.

Malleability and Ductility

Malleability and ductility are material properties that describe a substance's ability to deform under compressive stress and its ability to stretch into a wire, respectively. The exercise mentions that the substance can be pounded into thin sheets or drawn into wires, identifying it as both malleable and ductile.

Malleable materials, like certain metals, can withstand rolling and hammering to form thin sheets without breaking. Similarly, ductile materials can be extended into wires. These two properties are important for various manufacturing processes and are highly valued in industries that require metalworking. For educational purposes, invoking common examples like aluminum foil (malleability) and copper wires (ductility) can make these concepts more tangible for students.