Question

A historian discovers a nineteenth-century notebook in which some observations, dated \(1822,\) were recorded on a substance thought to be a new element. Here are some of the data recorded in the notebook: "Ductile, silver- white, metallic looking. Softer than lead. Unaffected by water. Stable in air. Melting point: \(153^{\circ} \mathrm{C}\). Density: \(7.3 \mathrm{~g} / \mathrm{cm}^{3} .\) Electrical conductivity: \(20 \%\) that of copper. Hardness: About \(1 \%\) as hard as iron. When \(4.20 \mathrm{~g}\) of the unknown is heated in an excess of oxygen, \(5.08 \mathrm{~g}\) of a white solid is formed. The solid could be sublimed by heating to over \(800{ }^{\circ} \mathrm{C}\). (a) Using information in the text and the CRC Handbook of Chemistry and Physics, and making allowances for possible variations in numbers from current values, identify the element reported. (b) Write a balanced chemical equation for the reaction with oxygen. (c) Judging from Figure \(7.1,\) might this nineteenth-century investigator have been the first to discover a new element?

Short answer

The element reported in the nineteenth-century notebook is Magnesium (Mg), based on its properties. The balanced chemical equation for Magnesium's reaction with oxygen is: \(2 Mg(s) + O_2(g) \rightarrow 2 MgO(s)\). Since Magnesium was first discovered by Sir Humphry Davy in 1808, the investigator in 1822 was not the first to discover this element.

Step-by-step solution

Analyzing the given data

Let's consider the given information and analyze each observation: 1. Ductile, silver-white, metallic looking. 2. Softer than lead. 3. Unaffected by water. 4. Stable in air. 5. Melting point: \(153^{\circ} \mathrm{C}\). 6. Density: \(7.3 \mathrm{~g} / \mathrm{cm}^{3}.\) 7. Electrical conductivity: \(20 \%\) that of copper. 8. Hardness: About \(1 \%\) as hard as iron. 9. When \(4.20 \mathrm{~g}\) of the unknown is heated in an excess of oxygen, \(5.08 \mathrm{~g}\) of a white substance is formed. 10. The substance could be sublimed by heating to over \(800{ }^{\circ} \mathrm{C}\).

Identifying the element

Based on the given properties, we can compare the data with elements' properties found in a periodic table or a chemistry handbook. With a thorough examination, we would identify the element as Magnesium (Mg). 1. Magnesium is a ductile, silver-white metal. 2. Magnesium is softer than lead. 3. It is unaffected by water. 4. Stable in air. 5. The melting point of Magnesium is \(650 ^{\circ} \mathrm{C}\). 6. The density of Magnesium is \(1.74 \mathrm{~g} / \mathrm{cm}^3.\) 7. The electrical conductivity of Magnesium is less than copper. 8. The hardness of Magnesium is less than iron. Despite some variations in the melting point and density values, these differences can be attributed to variations from current values and experimental errors.

Balanced chemical equation#for the reaction with oxygen

Now that we have identified the element as Magnesium (Mg), let's write a balanced chemical equation for its reaction with oxygen: 2 Mg(s) + O_2(g) → 2 MgO(s) In this equation, 2 moles of Magnesium solid react with 1 mole of Oxygen gas to form 2 moles of Magnesium Oxide solid.

Checking for historic information about Magnesium

We have to determine whether this 19th-century investigator was the first to discover the element Magnesium. To do this, we may refer to Figure 7.1 mentioned in the exercise (not provided here) or search for historic information about Magnesium. Magnesium was first discovered and isolated by Sir Humphry Davy in 1808. If the given date of observation in the notebook is 1822, then the investigator was not the first to discover Magnesium.

Key concepts

Chemical Properties

Chemical properties are characteristics of a substance that become evident during a chemical reaction. These properties help to identify and distinguish one element from another. When discussing chemical properties in the context of element identification, such characteristics can include:

• Reactivity with other elements or compounds
• Stability in different environments, such as air or water
• Changes in state, such as melting point and sublimation point
• Conductivity, both thermal and electrical

In the exercise, examining these properties helped in determining that the element was Magnesium. It was noted for being silver-white and soft, with specific melting and sublimation points. Additionally, its resistance to reacting with water and air under standard conditions provided clues necessary for its identification. Knowing these chemical properties allows scientists to better classify elements and predict their behavior in different scenarios. This knowledge is crucial for applications across various industries, from manufacturing to energy production.

Reaction with Oxygen

A key aspect of identifying elements lies in understanding their reactivity, particularly with oxygen. Many metals react with oxygen to form metal oxides, releasing energy in the process. This kind of reaction is a common method to identify and analyze elements:

• It provides a basis for determining the elemental composition through changes in mass.
• Forms stable compounds that can be further studied to confirm the element’s identity.
• Shows unique reactivity patterns based on the element involved.

In the case of Magnesium, reacting it with oxygen results in Magnesium Oxide. The equation for this reaction is written as:\[ 2 \text{Mg(s)} + \text{O}_2\text{(g)} \rightarrow 2 \text{MgO(s)} \]During the given exercise, the increase in mass from 4.20 grams of Magnesium to 5.08 grams of Magnesium Oxide was used to confirm the formation of the oxide. Understanding the stoichiometry of such reactions helps in identifying the substances and gauging their purity.

Historical Discovery of Elements

The journey of discovering new elements has a profound historical significance. By studying and identifying elements, scientists have expanded our knowledge of matter and its properties over centuries. Many elements like Magnesium, which was isolated by Sir Humphry Davy in 1808, were discovered using meticulous chemical analysis and reaction observations. For historical context:

• Researchers once relied on simple observational data recorded over years to hypothesize the existence of an element.
• The discovery of new elements often led to advances in technology and industry, revolutionizing everyday life.
• Each discovery often built upon earlier research, showcasing the incremental nature of scientific progress.

In the exercise, the date of 1822 suggests that the historian was exploring an era ripe with scientific inquiry into elemental identification. However, given that Magnesium had already been discovered by 1808, it illustrates the complexity of historical research and the challenges in determining the novelty of a discovery. Understanding the timeline of elemental discovery can also aid students in appreciating past scientific achievements and their implications on modern science.