Problem 19 - Chemistry: The Central Science in SI Units, Global Edition

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 appearance (silvery white, lustrous metal), melting point (\(649^{\circ}\mathrm{C}\)), boiling point (\(1105^{\circ}\mathrm{C}\)), density (\(1.738 \mathrm{~g}/\mathrm{cm}^{3}\) at \(20^{\circ}\mathrm{C}\)), malleability (can be pounded into thin sheets), ductility (can be drawn into wires), and electrical conductivity (good conductor of electricity). The chemical properties of the substance are its reaction with oxygen (burns in air, producing an intense white light) and reaction with chlorine (reacts 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. Melts at \(649^{\circ}\mathrm{C}\). 3. Boils at \(1105^{\circ}\mathrm{C}\). 4. Density at \(20^{\circ}\mathrm{C}\) is \(1.738 \mathrm{~g}/\mathrm{cm}^{3}\). 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. 8. Can be drawn into wires. 9. Good conductor of electricity.

Step 2: Identify Physical Properties

Let's find out the physical properties among the given observations. Remember, physical properties can be observed without changing the substance's identity. The physical properties are: 1. Silvery white, lustrous metal (appearance). 2. Melts at \(649^{\circ}\mathrm{C}\) (melting point). 3. Boils at \(1105^{\circ}\mathrm{C}\) (boiling point). 4. Density at \(20^{\circ}\mathrm{C}\) is \(1.738 \mathrm{~g}/\mathrm{cm}^{3}\) (density). 7. Can be pounded into thin sheets (malleability). 8. Can be drawn into wires (ductility). 9. Good conductor of electricity (electrical conductivity).

Step 3: Identify Chemical Properties

Now let's identify the chemical properties among the given observations. Chemical properties describe how a substance interacts with other substances or changes its chemical composition during chemical reactions. The chemical properties are: 5. Burns in air, producing an intense white light (reaction with oxygen). 6. Reacts with chlorine to give a brittle white solid (reaction with chlorine).

Step 4: Summarize the Physical and Chemical Properties

Based on our analysis, we can categorize the observations as follows: Physical Properties: 1. Appearance: Silvery white, lustrous metal. 2. Melting Point: \(649^{\circ}\mathrm{C}\). 3. Boiling Point: \(1105^{\circ}\mathrm{C}\). 4. Density: \(1.738 \mathrm{~g}/\mathrm{cm}^{3}\) at \(20^{\circ}\mathrm{C}\). 7. Malleability: Can be pounded into thin sheets. 8. Ductility: Can be drawn into wires. 9. Electrical Conductivity: Good conductor of electricity. Chemical Properties: 5. Reaction with Oxygen: Burns in air, producing an intense white light. 6. Reaction with Chlorine: Reacts with chlorine to give a brittle white solid.

Key Concepts

Chemical Properties

When we talk about chemical properties, we are focusing on how the substance behaves when it comes to reacting with other materials. These properties reveal the chemical nature and transformations a substance can undergo. It's about what the substance does when it interacts with other elements or compounds, not about what it looks like or feels like.
- One of the key observations in the original exercise is that the substance burns in air, producing an intense white light. This property indicates a reaction with oxygen, which is a chemical property.
- Another observation is the reaction with chlorine to form a brittle white solid. This signifies a chemical change where the substance combines with chlorine, resulting in a new product.
These reactions are essential for understanding how the substance behaves in different environments, providing insight into its potential uses and hazards.

Physical Properties

Physical properties are all about the description of a substance without changing its chemical identity. These properties can be observed or measured without altering the makeup of the material. Think of physical properties as the traits you can assess just by looking at and touching the substance.

• Appearance: The substance being a silvery white, lustrous metal falls under this category. It's all about how it looks in its natural state.
• Melting and Boiling Point: The substance melts at 649°C and boils at 1105°C. These temperature points tell us about the energy required to change states from solid to liquid to gas.
• Density: At 20°C, the density is 1.738 g/cm³. This property conveys the mass that the substance packs into a given volume, which can influence its applications.
• Malleability and Ductility: Being able to be pounded into sheets or drawn into wires indicates its flexibility or strength without breaking.
• Electrical Conductivity: Being a good conductor of electricity tells us about its potential use in electrical and related fields.

All these properties provide a clear understanding of what the substance is like in physical form, setting up expectations for handling and use.

Chemical Reactions

Chemical reactions are processes where substances interact to form new substances with different properties. Every chemical reaction involves the reorganization of atoms and bonds, resulting in new products. They can be as simple or complex as taking elements or compounds and forming entirely new compounds.
- In the context of the exercise, burning in air is an example of a chemical reaction where the substance combines with oxygen. Such reactions typically require energy and release energy in the form of light or heat. This particular reaction shows how the substance could be a source of intense energy when ignited. - The reaction with chlorine results in a brittle white solid, which emphasizes a transfer or sharing of electrons between atoms during the reaction. Such transitions lead to the formation of entirely new materials, which have different properties from the original reactants.
Chemical reactions are fundamental for creating new materials, and they are central to fields like chemistry, materials science, and engineering. Understanding how a substance reacts can open doors to new applications or even uncover potential hazards.