Chapter 2

Pepto-Bismol, which helps provide relief for an upset stomach, contains \(300 \mathrm{mg}\) bismuth subsalicylate, \(\mathrm{C}_{7} \mathrm{H}_{5} \mathrm{BiO}_{4},\) per tablet. (a) You take two tablets for your stomach distress. Calculate the amount of the "active ingredient" you are taking. (b) What mass of Bi did the two tablets contain?

Draw diagrams of each nanoscale situation given in parts (a) and (b). Represent atoms or monoatomic ions as circles; represent molecules or polyatomic ions by overlapping circles for the atoms that make up the molecule or ion; and distinguish among different kinds of atoms by labeling or shading the circles. In each case draw representations of at least five nanoscale particles. Your diagrams can be two-dimensional. (a) A crystal of solid sodium chloride (b) The sodium chloride from part (a) after it has been melted

Draw diagrams of each nanoscale situation given in parts (a)-(c). Represent atoms or monoatomic ions as circles; represent molecules or polyatomic ions by overlapping circles for the atoms that make up the molecule or ion; and distinguish among different kinds of atoms by labeling or shading the circles. In each case draw representations of at least five nanoscale particles. Your diagrams can be two-dimensional. (a) A sample of solid lithium nitrate, \(\mathrm{LiNO}_{3}\) (b) A sample of molten lithium nitrate (c) A molten sample of lithium nitrate after electrodes have been placed into it and a direct current applied to the electrodes

Which sets of values are possible? Why are the others not possible? Explain your reasoning. $$ \begin{array}{lrrrr} \hline & \begin{array}{l} \text { Mass } \\ \text { Number } \end{array} & \begin{array}{l} \text { Atomic } \\ \text { Number } \end{array} & \begin{array}{l} \text { Number of } \\ \text { Protons } \end{array} & \begin{array}{l} \text { Number of } \\ \text { Neutrons } \end{array} \\ \hline \text { (a) } & 19 & 42 & 19 & 23 \\ \text { (b) } & 235 & 92 & 92 & 143 \\ \text { (c) } & 53 & 131 & 131 & 79 \\ \text { (d) } & 32 & 15 & 15 & 15 \\ \text { (e) } & 14 & 7 & 7 & 7 \\ \text { (f) } & 40 & 18 & 18 & 40 \\ \hline \end{array} $$

Which sets of values are possible? Why are the others not possible? Explain your reasoning. $$ \begin{array}{lrrrr} \hline & \begin{array}{l} \text { Mass } \\ \text { Number } \end{array} & \begin{array}{l} \text { Atomic } \\ \text { Number } \end{array} & \begin{array}{l} \text { Number of } \\ \text { Protons } \end{array} & \begin{array}{l} \text { Number of } \\ \text { Neutrons } \end{array} \\ \hline \text { (a) } & 53 & 25 & 25 & 29 \\ \text { (b) } & 195 & 78 & 195 & 117 \\ \text { (c) } & 33 & 16 & 16 & 16 \\ \text { (d) } & 52 & 24 & 24 & 28 \\ \text { (e) } & 35 & 17 & 18 & 17 \\ \hline \end{array} $$

Potassium has three stable isotopes, \({ }^{39} \mathrm{~K},{ }^{40} \mathrm{~K},\) and \({ }^{41} \mathrm{~K}\) but \({ }^{40} \mathrm{~K}\) has a very low natural abundance. Which of the other two is the more abundant? (No calculation should be necessary.)

Lithium has two stable isotopes, \({ }^{6} \mathrm{Li}\) and \({ }^{7} \mathrm{Li}\). The atomic weight of lithium is 6.941 . Without doing a calculation, explain which is the more abundant isotope.

Which member of each pair has the greater number of atoms? Explain why. (a) \(1 \mathrm{~mol} \mathrm{Cl}\) or \(1 \mathrm{~mol} \mathrm{Cl}_{2}\) (b) 1 molecule \(\mathrm{O}_{2}\) or \(1 \mathrm{~mol} \mathrm{O}_{2}\) (c) 1 nitrogen atom or 1 nitrogen molecule (d) \(6.032 \times 10^{23}\) fluorine molecules or \(1 \mathrm{~mol}\) fluorine molecules (e) \(20.3 \mathrm{~g} \mathrm{Ne}\) or \(1 \mathrm{~mol} \mathrm{Ne}\) (f) 1 molecule \(\mathrm{Br}_{2}\) or \(159.8 \mathrm{~g} \mathrm{Br}_{2}\) (g) \(107.9 \mathrm{~g} \mathrm{Ag}\) or \(9.6 \mathrm{~g} \mathrm{Li}\) (h) \(58.9 \mathrm{~g} \mathrm{Co}\) or \(58.9 \mathrm{~g} \mathrm{Cu}\) (i) \(1 \mathrm{~g}\) calcium or \(6.022 \times 10^{23}\) calcium atoms (j) \(1 \mathrm{~g}\) chlorine atoms or \(1 \mathrm{~g}\) chlorine molecules

Which member of each pair has the greater mass? Explain why. (a) \(1 \mathrm{~mol}\) iron or \(1 \mathrm{~mol}\) aluminum (b) \(6.022 \times 10^{24}\) lead atoms or 1 mol lead (c) 1 copper atom or \(1 \mathrm{~mol}\) copper (d) \(1 \mathrm{~mol} \mathrm{Cl}\) or \(1 \mathrm{~mol} \mathrm{Cl}_{2}\) (e) \(1 \mathrm{~g}\) oxygen atoms or \(1 \mathrm{~g}\) oxygen molecules (f) \(23.4 \mathrm{~g} \mathrm{Mg}\) or \(1 \mathrm{~mol} \mathrm{Mg}\) (g) \(1 \mathrm{~mol} \mathrm{Na}\) or \(1 \mathrm{~g} \mathrm{Na}\) (h) \(4.1 \mathrm{~g} \mathrm{He}\) or \(6.022 \times 10^{23} \mathrm{He}\) atoms (i) 1 molecule \(\mathrm{I}_{2}\) or \(1 \mathrm{~mol} \mathrm{I}_{2}\) (j) 1 oxygen molecule or 1 oxygen atom

One way to solve problems is to find an analogy between what you know and what you need to determine. For example, if you know that the formula of magnesium oxide is \(\mathrm{MgO}\), and that sulfur is in Group \(6 \mathrm{~A}\) along with oxygen, by analogy the formula of magnesium sulfide is MgS. By analogy with sulfur or phosphorus compounds, name these compounds: (a) \(\mathrm{Na}_{2} \mathrm{SeO}_{3}\) (b) \(\mathrm{AlSbO}_{4}\) (c) \(\mathrm{K}_{3} \mathrm{AsO}_{4}\) (d) \(\mathrm{Ag}_{2} \mathrm{TeO}_{4}\)

When asked to draw all the possible constitutional isomers for \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O},\) a student drew these structures. The student's instructor said some of the structures were identical. (a) How many actual isomers are there? (b) Which structures are identical? (i) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{OH}\) (ii) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{O}-\mathrm{CH}_{3}\) (iii) \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

The formula for thallium nitrate is \(\mathrm{TINO}_{3}\). Based on this information, what would be the formulas for thallium carbonate and thallium sulfate?

The name given with each of these formulas is incorrect. What are the correct names? (a) \(\mathrm{CaF}_{2}\), calcium difluoride (b) \(\mathrm{CuO}\), copper oxide (c) \(\mathrm{NaNO}_{3},\) sodium nitroxide (d) \(\mathrm{NI}_{3}\), nitrogen iodide (e) \(\mathrm{FeCl}_{3}\), iron(I) chloride (f) \(\mathrm{Li}_{2} \mathrm{SO}_{4},\) dilithium sulfate

A high-quality analytical balance can weigh accurately to the nearest \(1.0 \times 10^{-4} \mathrm{~g}\). A sample of carbon weighed on this balance has a mass of \(1.000 \mathrm{mg}\). Calculate the number of carbon atoms in the sample. Given the precision of the balance, determine the maximum and minimum number of carbon atoms that could be in the sample.

The element bromine is \(\mathrm{Br}_{2}\), so the mass of a \(\mathrm{Br}_{2}\) molecule is the sum of the mass of its two atoms. Bromine has two isotopes. The mass spectrum of \(\mathrm{Br}_{2}\) produces three peaks with relative masses of \(157.836,159.834,\) and 161.832 , and relative heights of \(6.337,12.499,\) and 6.164, respectively. (a) What isotopes of bromine are present in each of the three peaks? (b) What is the mass of each bromine isotope? (c) What is the average atomic mass of bromine? (d) What is the abundance of each of the two bromine isotopes?

Uranium is used as a fuel, primarily in the form of uranium(IV) oxide, in nuclear power plants. This question considers some uranium chemistry. (a) A small sample of uranium metal \((0.169 \mathrm{~g})\) is heated to \(900{ }^{\circ} \mathrm{C}\) in air to give \(0.199 \mathrm{~g}\) of a dark green oxide, \(\mathrm{U}_{x} \mathrm{O}_{y} .\) How many moles of uranium metal were used? What is the empirical formula of the oxide \(\mathrm{U}_{x} \mathrm{O}_{y}\) ? What is the name of the oxide? How many moles of \(\mathrm{U}_{x} \mathrm{O}_{y}\) must have been obtained? (b) The oxide \(\mathrm{U}_{x} \mathrm{O}_{y}\) is obtained if \(\mathrm{UO}_{2} \mathrm{NO}_{3} \cdot n \mathrm{H}_{2} \mathrm{O}\) is heated to temperatures greater than \(800{ }^{\circ} \mathrm{C}\) in air. However, if you heat it gently, only the water of hydration is lost. If you have \(0.865 \mathrm{~g} \mathrm{UO}_{2} \mathrm{NO}_{3} \cdot n \mathrm{H}_{2} \mathrm{O}\) and obtain \(0.679 \mathrm{~g}\) \(\mathrm{UO}_{2} \mathrm{NO}_{3}\) on heating, how many molecules of water of hydration were there in each formula unit of the original compound?

A mixture contains only \(\mathrm{MgSO}_{4}\) and \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4} .\) If the mass percent of \(\mathrm{MgSO}_{4}\) in the mixture is \(32.0 \%,\) what is the mass percent of sulfate in the mixture?

Hemoglobin is an iron-containing protein (molar mass \(64,458 \mathrm{~g} / \mathrm{mol}\) ) that is responsible for oxygen transport in our blood. Hemoglobin is \(0.35 \%\) iron by mass. Calculate how many iron atoms are in each hemoglobin molecule.

There are three naturally occurring isotopes of potassium: \({ }^{39} \mathrm{~K} 38.963707 \mathrm{u} ;{ }^{40} \mathrm{~K} 39.963999 \mathrm{u}\); and \({ }^{41} \mathrm{~K}\) \(40.961825 \mathrm{u}\). The average atomic mass of potassium is \(39.0983 \mathrm{u}\) and the natural abundance of the lightest isotope is \(93.2581 \% .\) Calculate the natural abundances of the other two isotopes.

The diatomic compound \(\mathrm{BrCl}\) is a reddish-brown gas. Consider the naturally occurring isotopes of each element: $$ \begin{array}{lc} \hline \text { Isotope } & \text { Natural Abundance, \% } \\ \hline \text { Br-79 } & 50.69 \\ \text { Br-81 } & 49.31 \\ \text { Cl-35 } & 75.77 \\ \text { Cl-37 } & 24.23 \\ \hline \end{array} $$ (a) Name the compound. (b) Determine how many different types of \(\mathrm{BrCl}\) molecules are possible by using the sum of mass numbers as the criterion for type. (c) Determine which is the most abundant type in (b). (d) Determine which is the second most abundant type.

The stainless steel used in the Gateway Arch in St. Louis contains \(72.0 \% \mathrm{Fe}, 19.0 \% \mathrm{Cr}\), and the remainder is nickel. A 10.0 -g sample of this stainless steel is treated to convert the metals to their oxides: \(10.3 \mathrm{~g} \mathrm{Fe}_{2} \mathrm{O}_{3}, 2.71 \mathrm{~g}\) \(\mathrm{Cr}_{2} \mathrm{O}_{3},\) and \(1.14 \mathrm{~g} \mathrm{NiO} .\) Calculate the mass percent of each metal in the sample.

Galinstan, a gallium-indium-tin alloy, is a liquid at room temperature and is used as a nontoxic replacement for mercury in thermometers. Its mass ratio of gallium-toindium is \(3.186 .\) The mole ratio of indium-to-tin is \(2.223 .\) Calculate the mass percent composition of galinstan.

An adult human body contains \(6.0 \mathrm{~L}\) blood, which contains about \(15.5 \mathrm{~g}\) hemoglobin per \(100.0 \mathrm{~mL}\) blood. The molar mass of hemoglobin is approximately \(64,500 \mathrm{~g} / \mathrm{mol}\) and there is 4 mol iron per 1 mol hemoglobin. A news item claims that there is sufficient iron in the hemoglobin of the body that this iron, if it were in the form of metallic iron, could make a 3 -in. iron nail that weighs approximately \(3.7 \mathrm{~g}\). Show sufficient calculations to either support or refute the claim.

A 1.546 -g sample of magnesium metal is heated in sufficient air at a high temperature so that all of the magnesium reacts. The reaction forms \(2.512 \mathrm{~g} \mathrm{MgO}\) and a small quantity of another magnesium-containing compound that is \(72.24 \%\) magnesium by mass. (a) Determine the formula of the other magnesiumcontaining compound. (b) Name this compound. (c) Calculate what fraction of the original \(\mathrm{Mg}\) is in this second compound.

There are four binary potassium compounds of oxygen. They contain these mass percents of potassium: Compound I, \(83.0 \%\); Compound II, \(55.0 \%\); Compound III, \(44.9 \%\); and Compound IV, \(71.0 \%\). One compound has molar mass equal to \(110.2 \mathrm{~g} / \mathrm{mol}\). Use this information to determine the chemical formula of each compound.

Direct reaction of fluorine with xenon produces three different xenon fluorides. One of the compounds, call it compound "I", contains twice the mass of fluorine as another xenon fluoride. Let's call the latter one compound "II". The third compound, compound "III", contains 1.5 times the mass of fluorine contained in compound "I". Compound II contains \(77.5 \%\) Xe. (a) Determine the formula of each compound. (b) Name each compound.

A 20.00 g mixture of \(\mathrm{PCl}_{3}\) and \(\mathrm{PCl}_{5}\) contains 79.50 mass percent chlorine. (a) Name each compound. (b) Calculate the individual masses of \(\mathrm{PCl}_{3}\) and \(\mathrm{PCl}_{5}\) in the mixture.

The present average concentration (mass percent) of magnesium ions in seawater is \(0.13 \%\). A chemistry textbook estimates that if \(1.00 \times 10^{8}\) tons \(\mathrm{Mg}\) were taken out of the sea each year, it would take one million years for the Mg concentration to drop to \(0.12 \% .\) Do sufficient calculations to either verify or refute this statement. Assume that Earth is a sphere with a diameter of \(8000 \mathrm{mi}, 67 \%\) of which is covered by oceans to a depth of \(1 \mathrm{mi}\), and that no \(\mathrm{Mg}\) is washed back into the oceans at any time.

Through a series of reactions, a 12.3-g sample of potassium carbonate was chemically reacted so that all of its carbon was found in \(\mathrm{K}_{2} \mathrm{Zn}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{2} .\) Calculate the mass of \(\mathrm{K}_{2} \mathrm{Zn}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{2}\) formed.

A 4.22-g mixture of calcium chloride and sodium chloride was treated so that all of the calcium was converted to calcium carbonate. This product was then heated, converting it to \(0.959 \mathrm{~g}\) pure calcium oxide. Calculate the mass percent of calcium chloride in the original mixture.

A certain metal, M, forms two oxides, \(\mathrm{M}_{2} \mathrm{O}\) and MO. If the percent by mass of \(\mathrm{M}\) in \(\mathrm{M}_{2} \mathrm{O}\) is \(73.4 \%,\) calculate the percent by mass in MO.

If you heat Al with an element from Group \(6 \mathrm{~A},\) an ionic compound is formed that contains \(18.55 \%\) Al by mass. (a) What is the likely charge on the nonmetal in the compound formed? (b) Using \(\mathrm{X}\) to represent the nonmetal, what is the empirical formula for this ionic compound? (c) Which element in Group 6 A has been combined with \(\mathrm{Al}\) ?