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Chapter 1: Problem 16

In 1807 the English chemist Humphry Davy passed an electric current through molten potassium hydroxide and isolated a bright, shiny reactive substance. He claimed the discovery of a new element, which he named potassium. In those days, before the advent of modern instruments, what was the basis on which one could claim that a substance was an element?

Short Answer

Expert verified
In the early 1800s, substances were considered elements if they could not be broken down into simpler substances by any known chemical means. Humphry Davy's experiment involved using electrolysis to decompose molten potassium hydroxide (KOH) into potassium (K) and hydroxide (OH). By investigating potassium's unique properties and demonstrating that it could not be further broken down, Davy was able to claim the discovery of a new element, which he named potassium.

Step by step solution

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1. Understanding the historical context

During the time of Humphry Davy, substances were determined to be elements based on their inability to be broken down into simpler substances by any known chemical means. Davy's method of using electrical current to isolate elements was a new approach that enabled him to discover elements that were not discovered previously using only chemical reactions.
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2. Davy's experiment with molten potassium hydroxide

Davy isolated potassium by passing an electrical current through molten potassium hydroxide (KOH). This process is known as electrolysis. Through electrolysis, a chemical compound is decomposed into simpler substances when an electric current is passed through it. In his experiment, the molten potassium hydroxide broke down into its simpler components: potassium (K) and hydroxide (OH).
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3. Investigating the properties of potassium

In order to determine if a substance is a new element, it is important to investigate its properties. Potassium is a soft, reactive metal that looks bright and shiny when first isolated. It is highly reactive, especially with water, and forms strong alkaline solutions. These properties distinguish potassium from other known elements, suggesting that it could be a new element.
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4. Establishing potassium as a new element

To claim that potassium was an element, Davy needed to demonstrate that it cannot be broken down into simpler substances. At the time, no known chemical process could further break down potassium into other substances, indicating that it was a new element. In addition to this chemical evidence, potassium has a unique atomic weight, which serves as a key identifier for an element. In conclusion, based on the inability of potassium to be broken down into simpler substances and its unique properties and atomic weight, Humphry Davy was able to claim the discovery of a new element, which he named potassium.

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Most popular questions from this chapter

(a) The diameter of Earth at the equator is \(7926.381 \mathrm{mi}\). Round this number to three significant figures, and express it in standard exponential notation. (b) The circumference of Earth through the poles is \(40,008 \mathrm{~km}\). Round this number to four significant figures, and express it in standard exponential notation.

(a) After the label fell off a bottle containing a clear liquid believed to be benzene, a chemist measured the density of the liquid to verify its identity. A 25.0-mL portion of the liquid had a mass of \(21.95 \mathrm{~g}\). A chemistry handbook lists the density of benzene at \(15^{\circ} \mathrm{C}\) as \(0.8787 \mathrm{~g} / \mathrm{mL}\). Is the calculated density in agreement with the tabulated value? (b) An experiment requires \(15.0 \mathrm{~g}\) of cyclohexane, whose density at \(25{ }^{\circ} \mathrm{C}\) is \(0.7781 \mathrm{~g} / \mathrm{mL}\). What volume of cyclohexane should be used? (c) A spherical ball of lead has a diameter of \(5.0 \mathrm{~cm}\). What is the mass of the sphere if lead has a density of \(11.34 \mathrm{~g} / \mathrm{cm}^{3}\) ? (The volume of a sphere is \(\left(\frac{4}{3}\right) \pi r^{3}\) where \(r\) is the radius.)

Two students determine the percentage of lead in a sample as a laboratory exercise. The true percentage is \(22.52 \%\). The students' results for three determinations are as follows: 1\. \(22.52,22.48,22.54\) 2\. \(22.64,22.58,22.62\) (a) Calculate the average percentage for each set of data, and tell which set is the more accurate based on the average. (b) Precision can be judged by examining the average of the deviations from the average value for that data set. (Calculate the average value for each data set, then calculate the average value of the absolute deviations of each measurement from the average.) Which set is more precise?

Round each of the following numbers to four significant figures, and express the result in standard exponential notation: (a) \(102.53070\), (b) 656,980 , (c) \(0.008543210\), (d) \(0.000257870,(\mathrm{e})-0.0357202 .\)

A \(15.0\) -cm long cylindrical glass tube, sealed at one end, is filled with ethanol. The mass of ethanol needed to fill the tube is found to be \(11.86 \mathrm{~g}\). The density of ethanol is \(0.789 \mathrm{~g} / \mathrm{mL}\). Calculate the inner diameter of the tube in centimeters.
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