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Chapter 8: Problem 138

One allotropic form of an element \(X\) is a colorless crystalline solid. The reaction of \(\mathrm{X}\) with an excess amount of oxygen produces a colorless gas. This gas dissolves in water to yield an acidic solution. Choose one of the following elements that matches \(\mathrm{X}:\) (a) sulfur, (b) phosphorus, (c) carbon, (d) boron, and (e) silicon.

Short Answer

Expert verified
The element X is phosphorus.

Step by step solution

01

Review the characteristics of the unknown element

The unknown element, X, has an allotropic form which is a colorless crystalline solid. It reacts with oxygen to produce a colorless gas that subsequently dissolves in water to yield an acidic solution.
02

Analyze the known elements

Now, review each of the given elements (a) sulfur, (b) phosphorus, (c) carbon, (d) boron, and (e) silicon in reference to the characteristics of the unknown element.
03

Identify the matching element

On comparison, only phosphorus (in its white allotropic form) aligns with all of the given characteristics of the unknown element: it's a colorless crystalline solid, it reacts with an excess amount of oxygen to produce a colorless gas (phosphorus pentoxide), which dissolves in water to give an acidic solution (phosphoric acid).

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Most popular questions from this chapter

A student is given samples of three elements, \(\mathrm{X}, \mathrm{Y}\), and \(\mathrm{Z}\), which could be an alkali metal, a member of Group \(4 \mathrm{~A},\) and a member of Group \(5 \mathrm{~A} .\) She makes the following observations: Element X has a metallic luster and conducts electricity. It reacts slowly with hydrochloric acid to produce hydrogen gas. Element \(Y\) is a light-yellow solid that does not conduct electricity. Element \(Z\) has a metallic luster and conducts electricity. When exposed to air, it slowly forms a white powder. A solution of the white powder in water is basic. What can you conclude about the elements from these observations?

Explain why the first electron affinity of sulfur is \(200 \mathrm{~kJ} / \mathrm{mol}\) but the second electron affinity is \(-649 \mathrm{~kJ} / \mathrm{mol} .\)

Why is the radius of the lithium atom considerably larger than the radius of the hydrogen atom?

Explain why alkali metals have a greater affinity for electrons than alkaline earth metals.

A technique called photoelectron spectroscopy is used to measure the ionization energy of atoms. A sample is irradiated with UV light, and electrons are ejected from the valence shell. The kinetic energies of the ejected electrons are measured. Because the energy of the UV photon and the kinetic energy of the ejected electron are known, we can write $$ h \nu=I E+\frac{1}{2} m u^{2} $$ where \(\nu\) is the frequency of the UV light, and \(m\) and \(u\) are the mass and velocity of the electron, respectively. In one experiment the kinetic energy of the ejected electron from potassium is found to be \(5.34 \times 10^{-19} \mathrm{~J}\) using a UV source of wavelength \(162 \mathrm{nm} .\) Calculate the ionization energy of potassium. How can you be sure that this ionization energy corresponds to the electron in the valence shell (that is, the most loosely held electron)?
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