Chapter 2

Deuterium, \(^{2} \mathrm{H}(2.0140 \mathrm{u}),\) is sometimes used to replace the principal hydrogen isotope \(^{1} \mathrm{H}\) in chemical studies. The percent natural abundance of deuterium is 0.015\%. If it can be done with 100\% efficiency, what mass of naturally occurring hydrogen gas would have to be processed to obtain a sample containing \(2.50 \times 10^{21}^{2} \mathrm{H}\) atoms?

A particular silver solder (used in the electronics industry to join electrical components) is to have the atom ratio of \(5.00 \mathrm{Ag} / 4.00 \mathrm{Cu} / 1.00 \mathrm{Zn}\). What masses of the three metals must be melted together to prepare \(1.00 \mathrm{kg}\) of the solder?

A low-melting Sn-Pb-Cd alloy called eutectic alloy is analyzed. The mole ratio of tin to lead is 2.73: 1.00 and the mass ratio of lead to cadmium is 1.78: 1.00 . What is the mass percent composition of this alloy?

In an experiment, \(125 \mathrm{cm}^{3}\) of zinc and \(125 \mathrm{cm}^{3}\) of iodine are mixed together and the iodine is completely converted to \(164 \mathrm{cm}^{3}\) of zinc iodide. What volume of zinc remains unreacted? The densities of zinc, iodine, and zinc iodide are \(7.13 \mathrm{g} / \mathrm{cm}^{3}, 4.93 \mathrm{g} / \mathrm{cm}^{3}\) and \(4.74 \mathrm{g} / \mathrm{cm}^{3}\), respectively.

Atoms are spherical and so when silver atoms pack together to form silver metal, they cannot fill all the available space. In a sample of silver metal, approximately \(26.0 \%\) of the sample is empty space. Given that the density of silver metal is \(10.5 \mathrm{g} / \mathrm{cm}^{3}\), what is the radius of a silver atom? Express your answer in picometers.

Before \(1961,\) the standard for atomic masses was the isotope \(^{16} \mathrm{O},\) to which physicists assigned a value of exactly \(16 .\) At the same time, chemists assigned a value of exactly 16 to the naturally occurring mixture of the isotopes \(^{16} \mathrm{O},^{17} \mathrm{O},\) and \(^{18} \mathrm{O}\). Would you expect atomic masses listed in a 60 -year-old text to be the same, generally higher, or generally lower than in this text? Explain.

The German chemist Fritz Haber proposed paying off the reparations imposed against Germany after World War I by extracting gold from seawater. Given that (1) the amount of the reparations was \(\$ 28.8\) billion dollars, (2) the value of gold at the time was about \(\$ 21.25\) per troy ounce ( \(1 \text { troy ounce }=31.103 \mathrm{g}),\) and (3) gold occurs in seawater to the extent of \(4.67 \times 10^{17}\) atoms per ton of seawater \((1 \text { ton }=2000\) lb), how many cubic kilometers of seawater would have had to be processed to obtain the required amount of gold? Assume that the density of seawater is \(1.03 \mathrm{g} / \mathrm{cm}^{3}\) (Haber's scheme proved to be commercially infeasible, and the reparations were never fully paid.)

In your own words, define or explain these terms or symbols: (a) \(\underset{\mathbf{Z}}{\mathbf{A}} \mathbf{E} ;\) (b) \(\boldsymbol{\beta}\) particle; \(\mathbf{( c )}\) isotope; \(\mathbf{( d )}^{16} \mathbf{O}\) (e) molar mass.

Briefly describe (a) the law of conservation of mass (b) Rutherford's nuclear atom (c) weighted-average atomic mass (d) a mass spectrum

Explain the important distinctions between each pair of terms: (a) cathode rays and X-rays (b) protons and neutrons (c) nuclear charge and ionic charge (d) periods and groups of the periodic table (e) metal and nonmetal (f) the Avogadro constant and the mole

When \(10.0 \mathrm{g}\) zinc and \(8.0 \mathrm{g}\) sulfur are allowed to react, all the zinc is consumed, \(14.9 \mathrm{g}\) zinc sulfide is produced, and the mass of unreacted sulfur remaining is (a) \(2.0 \mathrm{g}\) (b) \(3.1 g\) (c) \(4.9 \mathrm{g}\) (d) impossible to predict from this information alone

One oxide of rubidium has \(0.187 \mathrm{g}\) O per gram of Rb. A possible O:Rb mass ratio for a second oxide of rubidium is (a) \(16: 85.5 ;\) (b) \(8: 42.7 ;\) (c) \(1: 2.674 ;\) (d) any of these.

Cathode rays (a) may be positively or negatively charged (b) are a form of electromagnetic radiation similar to visible light (c) have properties identical to \(\beta\) particles (d) have masses that depend on the cathode that emits them

The scattering of \(\alpha\) particles by thin metal foils established that (a) the mass of an atom is concentrated in a positively charged nucleus (b) electrons are fundamental particles of all matter (c) all electrons carry the same charge (d) atoms are electrically neutral

Which of the following have the same charge and approximately the same mass? (a) an electron and a proton; (b) a proton and a neutron; (c) a hydrogen atom and a proton; (d) a neutron and a hydrogen atom; (e) an electron and an \(\mathrm{H}^{-}\) ion.

What is the correct symbol for the species that contains 18 neutrons, 17 protons, and 16 electrons?

The properties of magnesium will most resemble those of which of the following? (a) cesium; (b) sodium; (c) aluminum; (d) calcium; (e) manganese.

The two species that have the same number of electrons as \(^{3}\) th S are (a) \(^{32} \mathrm{Cl} ;\) (b) \(^{34} \mathrm{S}^{+} ;\) (c) \(^{33} \mathrm{P}^{+} ;\) (d) \(^{28} \mathrm{Si}^{2-}\) (e) \(^{35} S^{2-} ;(f)^{40} A r^{2+} ;(g)^{40} C a^{2+}\)

To four significant figures, all of the following masses are possible for an individual titanium atom except one. The exception is (a) 45.95 u; (b) 46.95 u; (c) 47.87 u; (d) 47.95 u; (e) 48.95 u; (f) 49.94 u.

The mass of the isotope \(\frac{84}{36} \mathrm{Xe}\) is 83.9115 u. If the atomic mass scale were redefined so that \(\frac{84}{36} \mathrm{Xe}=84 \mathrm{u},\) exactly, the mass of the \(^{12} \mathrm{C}\) isotope would be (a) \(11.9115 \mathrm{u}\) (b) \(11.9874 \mathrm{u} ;\) (c) \(12 \mathrm{u}\) exactly; \((\mathrm{d}) 120127 \mathrm{u} ;(\mathrm{e}) 12.0885 \mathrm{u}\)

A 5.585-kg sample of iron (Fe) contains (a) \(10.0 \mathrm{mol} \mathrm{Fe}\) (b) twice as many atoms as does \(600.6 \mathrm{g} \mathrm{C}\) (c) 10 times as many atoms as does \(52.00 \mathrm{g} \mathrm{Cr}\) (d) \(6.022 \times 10^{24}\) atoms

There are three common iron-oxygen compounds. The one with the greatest proportion of iron has one Fe atom for every \(\mathrm{O}\) atom and the formula \(\mathrm{FeO}\). A second compound has 2.327 g Fe per \(1.000 \mathrm{g} \mathrm{O},\) and the third has \(2.618 \mathrm{g}\) Fe per \(1.000 \mathrm{g}\) O. What are the formulas of these other two iron-oxygen compounds?

The four naturally occurring isotopes of strontium have the atomic masses 83.9134 u; 85.9093 u; 86.9089 u; and 87.9056 u. The percent natural abundance of the lightest isotope is \(0.56 \%\) and of the heaviest, \(82.58 \%\) Estimate the percent natural abundances of the other two. Why is this result only a rough approximation?

Gold is present in seawater to the extent of \(0.15 \mathrm{mg} /\) ton. Assume the density of the seawater is \(1.03 \mathrm{g} / \mathrm{mL}\) and determine how many \(\mathrm{Au}\) atoms could conceivably be extracted from 0.250 L of seawater \(\left(1 \text { ton }=2.000 \times 10^{3} \mathrm{lb} ; 1 \mathrm{kg}=2.205 \mathrm{lb}\right)\)

Appendix E describes a useful study aid known as concept mapping. Using the method presented in Appendix \(\mathrm{E}\), construct a concept map illustrating the different concepts in Sections \(2-7\) and \(2-8\).