Chapter 10

Determine the number of molecules of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) in 47.0 \(\mathrm{g}\).

What mass of iron(III) chloride contains \(2.35 \times 10^{23}\) chloride ions?

Calculate the moles of aluminum ions present in 250.0 \(\mathrm{g}\) of aluminum oxide \(\left(\mathrm{Al}_{2} \mathrm{O}_{3}\right) .\)

Calculate the number of sodium ions present in 25.0 \(\mathrm{g}\) of sodium chloride.

Determine the number of oxygen atoms present in 25.0 g of carbon dioxide.

Espresso There is \(1.00 \times 10^{2} \mathrm{mg}\) of caffeine in a shot of espresso. The chemical formula of caffeine is \(\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{N}_{4} \mathrm{O}_{2}\). Determine the moles of each element present in the caffeine in one shot of espresso.

Explain what is meant by percent composition.

What information must a chemist have to determine the molecular formula for a compound?

What is the difference between an empirical formula and a molecular formula? Provide an example.

When can the empirical formula be the same as the molecular formula?

Which of the following formulas - NO, \(\mathrm{N}_{2} \mathrm{O}, \mathrm{NO}_{2}, \mathrm{N}_{2} \mathrm{O}_{4}\), and \(\mathrm{N}_{2} \mathrm{O}_{5}-\) represent the empirical and molecular for- mulas of the same compound? Explain your answer.

Do all pure samples of a given compound have the same percent composition? Explain.

Iron Three naturally occurring iron compounds are pyrite (FeS \(_{2} )\) , hematite \(\left(\mathrm{Fe}_{2} \mathrm{O}_{3}\right),\) and siderite \(\left(\mathrm{FeCO}_{3}\right)\) Which contains the greatest percentage of iron?

Express the composition of each compound as the mass percent of its elements (percent composition). \begin{equation} \begin{array}{l}{\text { a. sucrose }\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right) \quad \text { c. magnetite }\left(\mathrm{Fe}_{3} \mathrm{O}_{4}\right)} \\ {\text { b. aluminum sulfate }\left(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\right)}\end{array} \end{equation}

When a 35.07 -g sample of phosphorus reacts with oxygen, a 71.00 -g sample of phosphorus oxide is formed What is the percent composition of the compound? What is the empirical formula for this compound?

Cholesterol Heart disease is ligh blood cholesterol levels. What is the percent composition of the elements in a molecule of cholesterol \(\left(\mathrm{C}_{27} \mathrm{H}_{45} \mathrm{OH}\right) ?\)

Caffeine The stimulant effect of coffee is due to caffeine, \(\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{N}_{4} \mathrm{O}_{2}\) . Calculate the molar mass of caffeine. Determine its percent composition.

Which titanium-containing mineral, rutile \(\left(\mathrm{TiO}_{2}\right)\) or ilmenite \(\left(\mathrm{FeTiO}_{3}\right),\) has the larger percentage of titanium?

Vitamin E Many plants contain vitamin \(\mathrm{E}\left(\mathrm{C}_{29} \mathrm{H}_{50} \mathrm{O}_{2}\right)\), a substance that some think slows the aging process in humans. What is the percent composition of vitamin E?

Artificial Sweetener Determine the percent composition of aspartame \(\left(\mathrm{C}_{14} \mathrm{H}_{18} \mathrm{N}_{2} \mathrm{O}_{5}\right),\) an artificial sweetener.

MSG Monosodium glutamate, known as MSG, is sometimes added to food to enhance flavor. Analysis deter- mined this compound to be \(35.5 \% \mathrm{C}, 4.77 \% \mathrm{H}, 8.29 \% \mathrm{N},\) \(13.6 \% \mathrm{Na},\) and 37.9\(\% \mathrm{O} .\) What is its empirical formula?

Patina The Statue of Liberty has turned green because of the formation of a patina. Two copper compounds, \(\mathrm{Cu}_{3}(\mathrm{OH})_{4} \mathrm{SO}_{4}\) and \(\mathrm{Cu}_{4}(\mathrm{OH})_{6} \mathrm{SO}_{4}\) , form this patina. Find the mass percentage of copper in each compound.

What is a hydrated compound? Use an example to illustrate your answer.

Desiccants Why are certain electronic devices transported with desiccants?

In a laboratory setting, how would you determine if a compound was a hydrate?

Write the formula for the following hydrates. \begin{equation} \begin{array}{l}{\text { a. nickel(II) chloride hexahydrate }} \\ {\text { b. cobalt(II) chloride hexahydrate }} \\ {\text { c. magnesium carbonate pentahydrate }} \\ {\text { d. sodium sulfate decahydrate }}\end{array} \end{equation}

Determine the mass percent of anhydrous sodium carbonate \(\left(\mathrm{Na}_{2} \mathrm{CO}_{3}\right)\) and water in sodium carbonate decahydrate \(\left(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}\right)\).

Chromium(III) nitrate forms a hydrate that is 40.50\(\%\) water by mass. What is its chemical formula?

Determine the percent composition of \(\mathrm{MgCO}_{3} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) and draw a pie graph to represent the hydrate.

What is the formula and name of a hydrate that is 85.3\(\%\) barium chloride and 14.7\(\%\) water?

Gypsum is hydrated calcium sulfate. A 4.89 -g sample of this hydrate was heated. After the water was removed, 3.87 g anhydrous calcium sulfate remained. Determine the formula for this hydrate and name the compound.

Borax Hydrated sodium tetraborate \(\left(\mathrm{Na}_{2} \mathrm{B}_{4} \mathrm{O}_{7} \times x \mathrm{H}_{2} \mathrm{O}\right)\) is commonly called borax. Chemical analysis indicates that this hydrate is 52.8\(\%\) sodium tetraborate and 47.2\(\%\) water. Determine the formula and name the hydrate.

Rank samples \(A-D\) from least number of atoms to greatest number of atoms. A: 1.0 mol of \(\mathrm{H}_{2} ; \mathrm{B} : 0.75\) mol of \(\mathrm{H}_{2} \mathrm{O} ; \mathrm{C} : 1.5 \mathrm{mol}\) of \(\mathrm{NaCl} ; \mathrm{D} : 0.50 \mathrm{mol}\) of \(\mathrm{Ag}_{2} \mathrm{S}\)

One atom of an unknown element has a mass of \(6.66 \times 10^{-23} \mathrm{g} .\) What is the identity of this element?

Skunks Analysis of skunk spray yields a molecule with \(44.77 \% \mathrm{C}, 7.46 \% \mathrm{H}\) and 47.76\(\% \mathrm{S}\) . What is the chemical formula for this molecule found in the spray from skunks that scientists think is partly responsible for the strong odor?

How many moles are present in 1.00 \(\mathrm{g}\) of each compound? \begin{equation} \begin{array}{l}{\text { a. L-tryptophan }\left(\mathrm{C}_{11} \mathrm{H}_{12} \mathrm{N}_{2} \mathrm{O}_{2}\right), \text { an essential amino acid }} \\ {\text { b. magnesium sulfate heptahydrate, also known as }} \\\ {\text { Epsom salts }} \\ {\text { c. propane }\left(\mathrm{C}_{5} \mathrm{H}_{8}\right), \text { a fuel }}\end{array} \end{equation}

A compound contains 6.0 \(\mathrm{g}\) of carbon and 1.0 \(\mathrm{g}\) of hydrogen, and has a molar mass of 42.0 \(\mathrm{g} / \mathrm{mol}\) . What are the compound's percent composition, empirical formula, and molecular formula?

Which of these compounds has the greatest percent of oxygen by mass: \(\mathrm{TiO}_{2}, \mathrm{Fe}_{2} \mathrm{O}_{3},\) or \(\mathrm{Al}_{2} \mathrm{O}_{3} ?\)

Mothballs Naphthalene, commonly found in mothballs, is composed of 93.7\(\%\) carbon and 6.3\(\%\) hydrogen. The molar mass of naphthalene is 128 \(\mathrm{g} / \mathrm{mol}\) . Determine the empirical and molecular formulas for naphthalene.

Which of these molecular formulas are also empirical formulas: ethyl ether \(\left(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}\right),\) aspirin \(\left(\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4}\right),\) butyl dichloride \(\left(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\right),\) glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right) ?\)

Apply Concepts A mining company has two possible sources of copper: chalcopyrite (CuFeS \(_{2} )\) and chalcocite \(\left(\mathrm{Cu}_{2} \mathrm{S}\right)\) . If the mining conditions and the extraction of copper from the ore were identical for each of the ores, which ore would yield the greater quantity of copper? Explain your answer.

Design a concept map that illustrates the mole concept. Include the terms moles, Avogadro's mumber, molar mass, number of particles, percent composition, empirical formula, and molecular formula.

Two different compounds are composed of Elements \(\mathrm{X}\) and \(\mathrm{Y} .\) The formulas of the compounds are \(\mathrm{X}_{2} \mathrm{Y}_{3}\) and \(\mathrm{XY}\) . A 0.25 mol sample of XY has a mass of \(17.96 \mathrm{g},\) and a 0.25 mol sample of \(\mathrm{X}_{2} \mathrm{Y}_{3}\) has a mass of 39.92 \(\mathrm{g} .\) \begin{equation} \begin{array}{l}{\text { a. What are the atomic masses of elements } X \text { and } Y ?} \\ {\text { b. What are the formulas for the compounds? }}\end{array} \end{equation}

Express each answer with the correct number of significant figures. (Chapter 2\()\) \begin{equation} \begin{array}{l}{\text { a. } 18.23-456.7} \\ {\text { b. } 4.233 \div 0.0131} \\ {\text { c. }(82.44 \times 4.92)+0.125}\end{array} \end{equation}

Making Candy A recipe for pralines calls for the candy mixture to be heated until it reaches the "soft ball" stage, at about \(236^{\circ} \mathrm{F}\) . Can a Celsius thermometer with a range of \(-10\) to \(110^{\circ} \mathrm{C}\) be used to determine when the "soft ball" stage is reached? (Chapter 2\()\)

Contrast atomic number and mass number. Compare these numbers for isotopes of an element. (Chapter 4\()\)

Given the elements Ar, \(\mathrm{Cs}, \mathrm{Br}\) , and Ra, identify those that form positive ions. Explain your answer. (Chapter 7\()\)

Write the formula and name the compound formed when each pair of elements combine. (Chapter 7) \begin{equation} \begin{array}{l}{\text { a. barium and chlorine }} \\ {\text { b. aluminum and selenium }} \\ {\text { c. calcium and phosphorus }}\end{array} \end{equation}

Write balanced equations for each reaction. (Chapter 9) \begin{equation} \begin{array}{l}{\text { a. Magnesium metal and water combine to form solid }} \\\ {\text { magnesium hydroxide and hydrogen gas. }} \\ {\text { b. Dinitrogen tetroxide gas decomposes into nitrogen }} \\ {\text { dioxide gas. }} \\ {\text { c. Aqueous solutions of sulfuric acid and potassium }} \\\ {\text { hydroxide undergo a double-replacement reaction. }}\end{array} \end{equation}

Avogadro Research and report on the life of Italian chemist Amedeo Avogadro \((1776-1856)\) and how his work led scientists to determine the number of partides in a mole.