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Chapter 7: Problem 102

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

Expert verified
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

01

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 \(800{ }^{\circ} \mathrm{C}\).
02

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.
03

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.
04

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.

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Most popular questions from this chapter

Identify at least two ions that have the following ground-state electron configurations: (a) \([\mathrm{Ar}] ;\) (b) \([\mathrm{Ar}] 3 d^{5}\); (c) \([\mathrm{Kr}] 5 s^{2} 4 d^{10}\)

Identify each statement as true or false. If it is false, rewrite it so that it is true: (a) Ionization energies are always negative quantitites. (b) Oxygen has a larger first ionization energy than fluorine. (c) The second ionization energy of an atom is always greater than its first ionization energy.

Make a simple sketch of the shape of the main part of the periodic table, as shown. (a) Ignoring \(\mathrm{H}\) and He, write a single straight arrow from the element with the smallest bonding atomic radius to the element with the largest. Ignoring \(\mathrm{H}\) and He, write a single straight arrow from the element with the smallest first ionization energy to the element with the largest. (c) What significant observation can you make from the arrows you drew in parts (a) and (b)? [Sections 7.3 and 7.4]

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Write balanced equations for the following reactions: (a) potassium oxide with water, (b) diphosphorus trioxide with water, (c) chromium(III) oxide with dilute hydrochloric acid, (d) selenium dioxide with aqueous potassium hydroxide.
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