Problem 18 - Chemistry: The Central Science

Question

Read the following description of the element zinc, and indicate which are physical properties and which are chemical properties. Zinc is a silver-gray- colored metal that melts at \(420^{\circ} \mathrm{C}\). When zinc granules are added to dilute sulfuric acid, hydrogen is given off and the metal dissolves. Zinc has a hardness on the Mohs scale of \(2.5\) and a density of \(7.13 \mathrm{~g} / \mathrm{cm}^{3}\) at \(25^{\circ} \mathrm{C}\). It reacts slowly with oxygen gas at elevated temperatures to form zinc oxide, \(\mathrm{ZnO}\).

Step-by-Step Solution

Answer

The physical properties of zinc are its silver-gray color, melting point of \(420^{\circ} \mathrm{C}\), hardness on the Mohs scale of 2.5, and density of \(7.13 \mathrm{~g} / \mathrm{cm}^{3}\) at \(25^{\circ} \mathrm{C}\). The chemical properties of zinc are its reactions with sulfuric acid and oxygen gas to produce hydrogen and zinc oxide, respectively.

Step 1: 1. Silver-gray color

The color of a substance is a physical property because it can be observed or measured without changing the identity of the substance. In this case, zinc's silver-gray color is a physical property.

Step 2: 2. Melting point

The melting point of a substance is the temperature at which it changes from a solid to a liquid. This is a physical property because it can be measured without changing the identity of the substance. So, zinc's melting point of \(420^{\circ} \mathrm{C}\) is a physical property.

Step 3: 3. Reaction with sulfuric acid

When zinc granules are added to dilute sulfuric acid, hydrogen is given off, and the metal dissolves. This is a chemical property because it describes how zinc reacts with another substance (sulfuric acid) to produce new substances (hydrogen and a dissolved zinc compound).

Step 4: 4. Hardness on the Mohs scale

Hardness is a measure of a material's resistance to deformation, which is a physical property. The Mohs scale is a qualitative scale used to classify the hardness of minerals. Zinc's Mohs hardness of 2.5 is a physical property.

Step 5: 5. Density

Density is the ratio of mass to volume for a substance. It is a physical property because it can be measured without changing the identity of the substance. Zinc's density of \(7.13 \mathrm{~g} / \mathrm{cm}^{3}\) at \(25^{\circ} \mathrm{C}\) is a physical property.

Step 6: 6. Reaction with oxygen gas

The reaction of zinc with oxygen gas at elevated temperatures to form zinc oxide is a chemical property. It describes how zinc reacts with another substance (oxygen) under specific conditions (elevated temperatures) to produce a new substance (zinc oxide). In summary, the physical properties of zinc mentioned in the description are its silver-gray color, melting point, hardness on the Mohs scale, and density. The chemical properties are its reactions with sulfuric acid and oxygen gas.

Key Concepts

Physical Properties of Elements

Understanding the physical properties of elements such as zinc is crucial for grasping how these substances interact with their environment without altering their chemical identity. Physical properties can be observed and measured and include aspects such as color, melting point, hardness, and density.

For example, zinc's silvery-gray color allows us to visually identify the metal. This characteristic, along with the metal's melting point of \(420^{\text{\tiny o}}C\), which indicates the temperature at which zinc transitions from solid to liquid, are intrinsic features that do not involve a chemical transformation.

The hardness of an element, scaled on Mohs' scale, gives us an idea about its resistance to being scratched. With zinc's Mohs hardness of 2.5, we understand it is a relatively soft metal. Lastly, the density of zinc provides us with its mass per unit volume, \(7.13 \frac{g}{cm^3}\), offering us insight into its compactness and how it will feel when we handle it. These physical attributes are essential in various applications, from design to functionality.

Chemical Properties of Elements

While the physical properties of an element like zinc can be measured or observed easily, its chemical properties describe zinc's ability to undergo changes that transform it into a new substance. One such property is zinc’s behavior when it interacts with dilute sulfuric acid—producing hydrogen gas and a dissolved zinc compound, a reaction that is essential in validating zinc's reactivity and its applications in industries such as galvanization

Another chemical property is zinc's reaction with oxygen when heated. This reaction results in the formation of zinc oxide (\(ZnO\)), a compound used in paints, foods, and sunscreens for its protective properties. Understanding these chemical properties is key for students, as they influence how elements like zinc are harnessed in chemical processes and manufacturing.

Reactivity of Metals

Reactivity in metals such as zinc dictates how they will chemically interact with other substances such as acids, water, and oxygen. Reactivity is influenced by an element's electron configuration and its position in the periodic table.

Metals like zinc, while not the most reactive, still participate in various reactions, such as the slow formation of zinc oxide when heated in the presence of oxygen. Another demonstration of its reactivity is seen when zinc granules are placed in sulfuric acid, which leads to a chemical reaction producing hydrogen gas and a zinc sulfate solution.

This concept of reactivity is especially important as it determines how metals can be used. For instance, zinc's moderate reactivity makes it suitable for roles like corrosion-resistant coating for other metals, as well as an important component in batteries and alloys.

Metals and Nonmetals

In exploring the world of elements, distinguishing between metals like zinc and nonmetals is a fundamental concept. Metals usually have certain shared characteristics such as good electrical and thermal conductivity, malleability, and a shiny luster. Conversely, nonmetals tend to be brittle when solid, poor conductors of heat and electricity, and lack metallic luster.

Zinc is classified as a metal and displays several metallic properties such as having a high density and the ability to conduct heat and electricity. Its use in galvanization, which involves coating steel or iron with zinc to prevent rusting, exemplifies the practical applications of these metallic traits. Understanding the differences between metals and nonmetals helps students predict behavior and usage scenarios for these materials, playing a crucial role in disciplines such as chemistry and materials science.