Chapter 3

Write "true" or "false" for each statement. (a) We balance chemical equations as we do because energy must be conserved. (b) If the reaction 2 \(\mathrm{O}_{3}(g) \rightarrow 3 \mathrm{O}_{2}(g)\) goes to completion and all \(\mathrm{O}_{3}\) is converted to \(\mathrm{O}_{2},\) then the mass of \(\mathrm{O}_{3}\) at the beginning of the reaction must be the same as the mass of \(\mathrm{O}_{2}\) at the end of the reaction. (c) You can balance the "water-splitting" reaction \(\mathrm{H}_{2} \mathrm{O}(I) \rightarrow \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)\) by writing it this way: \(\mathrm{H}_{2} \mathrm{O}_{2}(l) \rightarrow \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)\)

A key step in balancing chemical equations is correctly identifying the formulas of the reactants and products. For example, consider the reaction between calcium oxide, CaO(s), and \(\mathrm{H}_{2} \mathrm{O}(l)\) to form aqueous calcium hydroxide. (a) Write a balanced chemical equation for this combination reaction, having correctly identified the product as \(\mathrm{Ca}(\mathrm{OH})_{2}(a q)\) . (b) Is it possible to balance the equation if you incorrectly identify the product as \(\mathrm{CaOH}(a q),\) and if so, what is the equation?

Balance the following equations: $$ \begin{array}{l}{\text { (a) } \mathrm{CO}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)} \\ {\text { (b) } \mathrm{N}_{2} \mathrm{O}_{5}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{HNO}_{3}(a q)} \\ {\text { (c) } \mathrm{CH}_{4}(g)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{CCl}_{4}(l)+\mathrm{HCl}(g)} \\ {\text { (d) } \mathrm{Zn}(\mathrm{OH})_{2}(s)+\mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l)}\end{array} $$

Balance the following equations: $$ \begin{array}{l}{\text { (a) } \mathrm{Li}(s)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{Li}_{3} \mathrm{N}(s)} \\ {\text { (b) } \mathrm{TiCl}_{4}(l)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{TiO}_{2}(s)+\mathrm{HCl}(a q)} \\ {\text { (c) } \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (d) } \mathrm{AlCl}_{3}(s)+\mathrm{Ca}_{3} \mathrm{N}_{2}(s) \longrightarrow \mathrm{AlN}(s)+\mathrm{CaCl}_{2}(s)}\end{array} $$

Balance the following equations: $$ \begin{array}{l}{\text { (a) } \mathrm{Al}_{4} \mathrm{C}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Al}(\mathrm{OH})_{3}(s)+\mathrm{CH}_{4}(g)} \\ {\text { (b) } \mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (c) } \mathrm{Fe}(\mathrm{OH})_{3}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l)} \\ {\text { (d) } \mathrm{Mg}_{3} \mathrm{N}_{2}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{MgSO}_{4}(a q)+\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(a q)}\end{array} $$

Write balanced chemical equations corresponding to each of the following descriptions: (a) Solid calcium carbide, \(\mathrm{CaC}_{2}\) , reacts with water to form an aqueous solution of calcium hydroxide and acetylene gas, \(\mathrm{C}_{2} \mathrm{H}_{2}\) . (b) When solid potassium chlorate is heated, it decomposes to form solid potassium chloride and oxygen gas. (c) Solid zinc metal reacts with sulfuric acid to form hydrogen gas and an aqueous solution of zinc sulfate. (d) When liquid phosphorus trichloride is added to water, it reacts to form aqueous phosphorous acid, \(\mathrm{H}_{3} \mathrm{PO}_{3}(a q)\), and aqueous hydrochloric acid. (e) When hydrogen sulfide gas is passed over solid hot iron(III) hydroxide, the resulting reaction produces solid iron(II) sulfide and gaseous water.

Write balanced chemical equations to correspond to each of the following descriptions: (a) When sulfur trioxide gas reacts with water, a solution of sulfuric acid forms. (b) Boron sulfide, \(B_{2} S_{3}(s),\) reacts violently with water to form dissolved boric acid, \(H_{3} B O_{3},\) and hydrogen sulfide gas. (c) Phosphine, PH \(_{3}(g),\) combusts in oxygen gas to form water vapor and solid tetraphosphorus decaoxide. (d) When solid mercury(II) nitrate is heated, it decomposes to form solid mercury(II) oxide, gaseous nitrogen dioxide, and oxygen.(e) Copper metal reacts with hot concentrated sulfuric acid solution to form aqueous copper(II) sulfate, sulfur dioxide gas, and water.

(a) When a compound containing \(\mathrm{C}, \mathrm{H},\) and \(\mathrm{O}\) is completely combusted in air, what reactant besides the hydrocarbon is involved in the reaction? (b) What products form in this reaction? (c) What is the sum of the coefficients in the balanced chemical equation for the combustion of one mole of acetone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(l),\) in air?

Write a balanced chemical equation for the reaction that occurs when (a) \(\mathrm{Mg}(s)\) reacts with \(\mathrm{Cl}_{2}(g) ;\) (b) barium carbonate decomposes into barium oxide and carbon dioxide gas when heated; (c) the hydrocarbon styrene, \(\mathrm{C}_{8} \mathrm{H}_{8}(l),\) is combusted in air; (d) dimethylether, \(\mathrm{CH}_{3} \mathrm{OCH}_{3}(g),\) is combusted in air.

Write a balanced chemical equation for the reaction that occurs when (a) titanium metal reacts with \(\mathrm{O}_{2}(g) ;(\mathbf{b})\) silver(I)oxide decomposes into silver metal and oxygen gas when heated; (c) propanol, \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}(l)\) burns in air; (d) methyl tert- butyl ether, \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}(l),\) burns in air.

Balance the following equations and indicate whether they are combination, decomposition, or combustion reactions: $$ \begin{array}{l}{\text { (a) } \mathrm{C}_{3} \mathrm{H}_{6}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (b) } \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow \mathrm{N}_{2} \mathrm{O}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (c) } \mathrm{C}_{5} \mathrm{H}_{6} \mathrm{O}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (d) } \mathrm{N}_{2}(g)+\mathrm{H}_{2}(g) \longrightarrow \mathrm{NH}_{3}(g)} \\\ {\text { (e) } \mathrm{K}_{2} \mathrm{O}(s)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{KOH}(a q)}\end{array} $$

Balance the following equations and indicate whether they are combination, decomposition, or combustion reactions: $$ \begin{array}{l}{\text { (a) } \mathrm{PbCO}_{3}(s) \longrightarrow \mathrm{PbO}(s)+\mathrm{CO}_{2}(g)} \\ {\text { (b) } \mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ {\text { (c) } \mathrm{Mg}(s)+\mathrm{N}_{2}(g) \longrightarrow \mathrm{Mg}_{3} \mathrm{N}_{2}(s)} \\ {\text { (d) } \mathrm{C}_{7} \mathrm{H}_{8} \mathrm{O}_{2}(l)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)} \\ \text { (e) } \mathrm{Al}(s)+\mathrm{Cl}_{2}(g) \longrightarrow \mathrm{AlCl}_{3}(s) \end{array} $$

Determine the formula weights of each of the following compounds: (a) nitric acid, HNO \(_{3} ;\) (b) \(\mathrm{KMnO}_{4} ;\) (c) \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) (d) quartz, SiO \(_{2} ;\) (e) gallium sulfide, (f) chromium(III) sulfate, (g) phosphorus trichloride.

Determine the formula weights of each of the following compounds: (a) nittrous oxide, \(\mathrm{N}_{2} \mathrm{O}\) , known as laughing gas and used as an anesthetic in dentistry; (b) benzoic acid; \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) a substance used as a food preservative; \((c) \mathrm{Mg}(\mathrm{OH})_{2},\) the active ingredient in milk of magnesia; (d) urea, \(\left(\mathrm{NH}_{2}\right)_{2} \mathrm{CO},\) a compound used as a nitrogen fertilizer; (e) isopentyl acetate, \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{C}_{5} \mathrm{H}_{11},\) responsible for the odor of bananas.

Calculate the percentage by mass of the indicated element in the following compounds: \((\mathbf{a})\) carbon in acetylene, \(\mathrm{C}_{2} \mathrm{H}_{2}, \mathrm{a}\) gas used in welding; \((\mathbf{b} )\) hydrogen in ascorbic acid, \(\mathrm{HC}_{6} \mathrm{H}_{7} \mathrm{O}_{6}\) also known as vitamin \(\mathrm{C} ;(\mathbf{c})\) hydrogen in ammonium sulfate, \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4},\) a substance used as a nitrogen fertilizer; \((\mathbf{d})\) platinum in \(\mathrm{PtCl}_{2}\left(\mathrm{NH}_{3}\right)_{2},\) a chemotherapy agent called cisplatin; \((\mathbf{e})\) oxygen in the female sex hormone estradiol, \(\mathrm{C}_{18} \mathrm{H}_{24} \mathrm{O}_{2} ;(\mathbf{f})\) carbon in capsaicin, \(\mathrm{C}_{18} \mathrm{H}_{27} \mathrm{NO}_{3},\) the compound that gives the hot taste to chili peppers.

(a) Write "true" or "false" for each statement. (a) A mole of horses contain a mole of horse legs. (b) A mole of water has a mass of 18.0 \(\mathrm{g} .\) (c) The mass of 1 molecule of water is 18.0 \(\mathrm{g}\) (d) A mole of NaCl (s) contains 2 moles of ions.

(a) What is the mass, in grams, of one mole of \(^{12} \mathrm{C} ?\) (b) How many carbon atoms are present in one mole of \(^{12} \mathrm{C} ?\)

Without doing any detailed calculations (but using a periodic table to give atomic weights), rank the following samples in order of increasing numbers of atoms: 0.50 mol \(\mathrm{H}_{2} \mathrm{O}, 23 \mathrm{g} \mathrm{Na}, 6.0 \times 10^{23} \mathrm{N}_{2}\) molecules.

Without doing any detailed calculations (but using a periodic table to give atomic weights, rank the following samples in order of increasing numbers of atoms: 42 gof NaHCO \(_{3}, 1.5 \mathrm{mol} \mathrm{CO}_{2}, 6.0 \times 10^{24} \mathrm{Ne}\) atoms.

What is the mass, in kilograms, of an Avogadro's number of people, if the average mass of a person is 160 \(\mathrm{lb}\) ? How does this compare with the mass of Earth, \(5.98 \times 10^{24} \mathrm{kg}\) ?

If Avogadro's number of pennies is divided equally among the 321 million men, women, and children in the United States, how many dollars would each receive? How does this compare with the gross domestic product (GDP) of the United States, which was \(\$ 17.419\) trillion in 2015\(?\) (The GDP is the total market value of the nation's goods and services.)

Calculate the following quantities: $$ \begin{array}{l}{\text { (a) mass, in grams, of } 1.50 \times 10^{-2} \text { mol CdS }} \\ {\text { (b) number of moles of } \mathrm{NH}_{4} \mathrm{Cl} \text { in } 86.6 \mathrm{g} \text { of this substance }} \\ {\text { (c) number of molecules in } 8.447 \times 10^{-2} \mathrm{mol} \mathrm{C}_{6} \mathrm{H}_{6}} \\ {\text { (d) number of } \mathrm{O} \text { atoms in } 6.25 \times 10^{-3} \mathrm{mol} \mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}}\end{array} $$

(a) What is the mass, in grams, of \(2.50 \times 10^{-3}\) mol of ammonium phosphate? (b) How many moles of chloride ions are in 0.2550 g of aluminum chloride? (c) What is the mass, in grams, of \(7.70 \times 10^{20}\) molecules of caffeine, \(\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{N}_{4} \mathrm{O}_{2} ?\) (d) What is the molar mass of cholesterol if 0.00105 \(\mathrm{mol}\) has a mass of 0.406 \(\mathrm{g}\) ?

(a) What is the mass, in grams, of 1.223 mol of iron( III) sulfate? (b) How many moles of ammonium ions are in 6.955 g of ammonium carbonate? (c) What is the mass, in grams, of \(1.50 \times 10^{21}\) molecules of aspirin, \(\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4} ?\) (d) What is the molar mass of diazepam (Valium') if 0.05570 mol has a mass of 15.86 \(\mathrm{g} ?\)

The molecular formula of allicin, the compound responsible for the characteristic smell of garlic, is \(\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{OS}_{2}\) . (a) What is the molar mass of allicin? (b) How many moles of allicin are present in 5.00 \(\mathrm{mg}\) of this substance? (c) How many molecules of allicin are in 5.00 \(\mathrm{mg}\) of this substance? (d) How many S atoms are present in 5.00 \(\mathrm{mg}\) of allicin?

The molecular formula of aspartame, the artificial sweetener marketed as NutraSweet, is \(\mathrm{C}_{14} \mathrm{H}_{18} \mathrm{N}_{2} \mathrm{O}_{5}\) . (a) What is the molar mass of aspartame? (b) How many moles of aspartame are present in 1.00 \(\mathrm{mg}\) of aspartame? (c) How many molecules of aspartame are present in 1.00 \(\mathrm{mg}\) of aspartame? (d) How many hydrogen atoms are present in 1.00 \(\mathrm{mg}\) of aspartame?

A sample of glucose, \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},\) contains \(1.250 \times 10^{21}\) carbon atoms. (a) How many atoms of hydrogen does it contain? (b) How many molecules of glucose does it contain? (c) How many moles of glucose does it contain? (d) What is the mass of this sample in grams?

A sample of the male sex hormone testosterone, \(\mathrm{C}_{19} \mathrm{H}_{28} \mathrm{O}_{2}\) , contains \(3.88 \times 10^{21}\) hydrogen atoms. (a) How many atoms of carbon does it contain? (b) How many molecules of testosterone does it contain? (c) How many moles of testosterone does it contain? (d) What is the mass of this sample in grams?

The allowable concentration level of vinyl chloride, \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}\) , in the atmosphere in a chemical plant is \(2.0 \times 10^{-6} \mathrm{g} / \mathrm{L}\) . How many moles of vinyl chloride in each liter does this represent? How many molecules per liter?

At least 25\(\mu \mathrm{g}\) of tetrahydrocannabinol \((\mathrm{THC}),\) the active ingredient in marijuana, is required to produce intoxication. The molecular formula of THC is \(\mathrm{C}_{21} \mathrm{H}_{30} \mathrm{O}_{2} .\) How many moles of THC does this 25\(\mu \mathrm{g}\) represent? How many molecules?

Give the empirical formula of each of the following compounds if a sample contains (a) 0.0130 mol \(\mathrm{C}, 0.0390 \mathrm{mol}\) \(\mathrm{H},\) and \(0.0065 \mathrm{mol} \mathrm{O} ;\) (b) \(11.66 \mathrm{g}\) iron and 5.01 \(\mathrm{g}\) oxygen; (c) \(40.0 \% \mathrm{C}, 6.7 \% \mathrm{H},\) and 53.3\(\%\) o by mass.

Determine the empirical formula of each of the following compounds if a sample contains \((\mathbf{a})0.104 \mathrm{mol} \mathrm{K}, 0.052 \mathrm{mol}\) \(\mathrm{C},\) and \(0.156 \mathrm{mol} \mathrm{O} ;(\mathbf{b}) 5.28 \mathrm{g} \mathrm{Sn}\) and \(3.37 \mathrm{g} \mathrm{F} ;(\mathbf{c}) 87.5 \% \mathrm{N}\) and 12.5\(\% \mathrm{H}\) by mass.

Determine the empirical formulas of the compounds with the following compositions by mass: $$ \begin{array}{l}{\text { (a) } 10.4 \% \mathrm{C}, 27.8 \% \mathrm{S}, \text { and } 61.7 \% \mathrm{Cl}} \\ {\text { (b) } 21.7 \% \mathrm{C}, 9.6 \% \mathrm{O}, \text { and } 68.7 \% \mathrm{F}} \\ {\text { (c) } 32.79 \% \mathrm{Na}, 13.02 \% \mathrm{Al}, \text { and the remainder } \mathrm{F}}\end{array} $$

Determine the empirical formulas of the compounds with the following compositions by mass: $$ \begin{array}{l}{\text { (a) } 55.3 \% \mathrm{K}, 14.6 \% \mathrm{P}, \text { and } 30.1 \% \mathrm{O}} \\ {\text { (b) } 24.5 \% \mathrm{Na}, 14.9 \% \mathrm{Si}, \text { and } 60.6 \% \mathrm{F}} \\ {\text { (c) } 62.1 \% \mathrm{C}, 5.21 \% \mathrm{H}, 12.1 \% \mathrm{N}, \text { and the remainder O }}\end{array} $$

A compound whose empirical formula is \(X F_{3}\) consists of 65\(\%\) F by mass. What is the atomic mass of \(X ?\)

What is the molecular formula of each of the following compounds? $$ \begin{array}{l}{\text { (a) empirical formula } \mathrm{CH}_{2}, \text { molar mass }=84.0 \mathrm{g} / \mathrm{mol}} \\ {\text { (b) empirical formula } \mathrm{NH}_{2} \mathrm{Cl} \text { , molar mass }=51.5 \mathrm{g} / \mathrm{mol}}\end{array} $$

What is the molecular formula of each of the following compounds? $$ \begin{array}{l}{\text { (a) empirical formula } \mathrm{HCO}_{2} \text { , molar mass }=90.0 \mathrm{g} / \mathrm{mol}} \\ {\text { (b) empirical formula } \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}, \text { molar mass }=88.0 \mathrm{g} / \mathrm{mol}}\end{array} $$

Determine the empirical and molecular formulas of each of the following substances: (a) Styrene, a compound used to make Styrofoam' cups and insulation, contains 92.3\(\% \mathrm{C}\) and 7.7\(\% \mathrm{H}\) by mass and has a molar mass of 104 \(\mathrm{g} / \mathrm{mol} .\) (b) Caffeine, a stimulant found in coffee, contains 49.5\(\% \mathrm{C}\) , \(5.15 \% \mathrm{H}, 28.9 \% \mathrm{N},\) and 16.5\(\% \mathrm{O}\) by mass and has a molar mass of 195 \(\mathrm{g} / \mathrm{mol} .\) (c) Monosodium glutamate (MSG), a flavor enhancer in certain foods, contains \(35.51 \% \mathrm{C}, 4.77 \% \mathrm{H}, 37.85 \% \mathrm{O}\) , \(8.29 \% \mathrm{N},\) and 13.60\(\% \mathrm{Na}\) , and has a molar mass of 169 \(\mathrm{g} / \mathrm{mol} .\)

Determine the empirical and molecular formulas of each of the following substances: (a) Ibuprofen, a headache remedy, contains 75.69\(\% \mathrm{C}\) , \(8.80 \% \mathrm{H},\) and 15.51\(\% \mathrm{O}\) by mass and has a molar mass of 206 \(\mathrm{g} / \mathrm{mol} .\) (b) Cadaverine, a foul-smelling substance produced by the action of bacteria on meat, contains 58.55\(\% \mathrm{C}\) , \(13.81 \% \mathrm{H},\) and 27.40\(\% \mathrm{N}\) by mass; its molar mass is 102.2 \(\mathrm{g} / \mathrm{mol}\) (c) Epinephrine (adrenaline), a hormone secreted into the bloodstream in times of danger or stress, contains 59.0\(\%\) C, \(7.1 \% \mathrm{H}, 26.2 \% \mathrm{O},\) and 7.7\(\% \mathrm{N}\) by mass; its molar mass is about 180 amu.

(a) Combustion analysis of toluene, a common organic solvent, gives 5.86 \(\mathrm{mg}\) of \(\mathrm{CO}_{2}\) and 1.37 \(\mathrm{mg}\) of \(\mathrm{H}_{2} \mathrm{O}\) . If the compound contains only carbon and hydrogen, what is its empirical formula? (b) Menthol, the substance can smell in mentholated cough drops, is composed of \(\mathrm{C}, \mathrm{H},\) and \(\mathrm{O} . \mathrm{A}\) 0.1005 -gsample of mentholis combusted, producing 0.2829 \(\mathrm{g}\) of \(\mathrm{CO}_{2}\) and 0.1159 \(\mathrm{g}\) of \(\mathrm{H}_{2} \mathrm{O} .\) What is the empirical formula for menthol? If menthol has a molar mass of 156 \(\mathrm{g} / \mathrm{mol}\) what is its molecular formula?

(a) The characteristic odor of pineapple is due to ethyl butyrate, a compound containing carbon, hydrogen, and oxygen. Combustion of 2.78 mg of ethyl butyrate produces 6.32 \(\mathrm{mg}\) of \(\mathrm{CO}_{2}\) and 2.58 \(\mathrm{mg}\) of \(\mathrm{H}_{2} \mathrm{O} .\) What is the empirical formula of the compound? (b) Nicotine, a component of tobacco, is composed of \(C, H,\) and \(N .\) A 5.250 -mg sample of nicotine was combusted, producing 14.242 \(\mathrm{mg}\) of \(\mathrm{CO}_{2}\) and 4.083 \(\mathrm{mg}\) of \(\mathrm{H}_{2} \mathrm{O} .\) What is the empirical formula for nicotine? If nicotine has a molar mass of \(160 \pm 5 \mathrm{g} / \mathrm{mol},\) what is its molecular formula?

Valproic acid, used to treat seizures and bipolar disorder, is composed of \(\mathrm{C}, \mathrm{H},\) and \(\mathrm{O} . \mathrm{A}\) . \(165-\mathrm{g}\) sample is combusted to produce 0.166 \(\mathrm{g}\) of water and 0.403 \(\mathrm{g}\) of carbon dioxide. What is the empirical formula for valproic acid? If the molar mass is \(144 \mathrm{g} / \mathrm{mol},\) what is the molecular formula?

Propenoic acid, \(\mathrm{C}_{3} \mathrm{H}_{4} \mathrm{O}_{2},\) is a reactive organic liquid that is used in the manufacturing of plastics, coatings, and adhesives. An unlabeled container is thought to contain this liquid. A 0.275 -g sample of the liquid is combusted to produce 0.102 gof water and 0.374 g carbon dioxide. Is the unknown liquid propenoic acid? Support your reasoning with calculations.

Washing soda, a compound used to prepare hard water for washing laundry, is a hydrate, which means that a certain number of water molecules are included in the solid structure. Its formula can be written as \(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot x \mathrm{H}_{2} \mathrm{O},\) where \(x\) is the number of moles of \(\mathrm{H}_{2} \mathrm{O}\) per mole of \(\mathrm{Na}_{2} \mathrm{CO}_{3} .\) When a 2.558 -g sample of washing soda is heated at \(125^{\circ} \mathrm{C}\) , all the water of hydration is lost, leaving 0.948 \(\mathrm{g}\) of \(\mathrm{Na}_{2} \mathrm{CO}_{3} .\) What is the value of \(x ?\)

Epsom salts, a strong laxative used in veterinary medicine, is a hydrate, which means that a certain number of water molecules are included in the solid structure. The formula for Epsom salts can be written as \(\mathrm{MgSO}_{4} \cdot x \mathrm{H}_{2} \mathrm{O},\) where \(x\) indicates the number of moles of \(\mathrm{H}_{2} \mathrm{O}\) per mole of \(\mathrm{MgSO}_{4}\) When 5.061 \(\mathrm{g}\) of this hydrate is heated to \(250^{\circ} \mathrm{C},\) all the water of hydration is lost, leaving 2.472 g of MgSO \(_{4} .\) What is the value of \(x ?\)

Hydrofluoric acid, HF(aq), cannot be stored in glass bottles because compounds called silicates in the glass are attacked by the HF(aq). Sodium silicate (Na \(_{2} \mathrm{SiO}_{3} ),\) for example, reacts as follows: $$ \mathrm{Na}_{2} \mathrm{SiO}_{3}(s)+8 \mathrm{HF}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{SiF}_{6}(a q)+2 \operatorname{NaF}(a q)+3 \mathrm{H}_{2} \mathrm{O}(l) $$ (a) How many moles of HF are needed to react with 0.300 mol of \(\mathrm{Na}_{2} \mathrm{SiO}_{3} ?\) (b) How many grams of NaF form when 0.500 mol of HF reacts with excess \(\mathrm{Na}_{2} \mathrm{SiO}_{3} ?\) (c) How many grams of \(\mathrm{Na}_{2} \mathrm{SiO}_{3}\) can react with 0.800 g of HF?

The reaction between potassium superoxide, \(\mathrm{KO}_{2},\) and \(\mathrm{CO}_{2}\) $$ 4 \mathrm{KO}_{2}+2 \mathrm{CO}_{2} \longrightarrow 2 \mathrm{K}_{2} \mathrm{CO}_{3}+3 \mathrm{O}_{2} $$ is used as a source of \(\mathrm{O}_{2}\) and absorber of \(\mathrm{CO}_{2}\) in self-contained breathing equipment used by rescue workers. (a) How many moles of \(\mathrm{O}_{2}\) are produced when 0.400 \(\mathrm{mol}\) of \(\mathrm{KO}_{2}\) reacts in this fashion? (b) How many grams of \(\mathrm{KO}_{2}\) are needed to form 7.50 \(\mathrm{g}\) of \(\mathrm{O}_{2} ?\) (c) How many grams of \(\mathrm{CO}_{2}\) are used when 7.50 \(\mathrm{g}\) of \(\mathrm{O}_{2}\) are produced?

An iron ore sample contains \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) together with other substances. Reaction of the ore with CO produces iron metal: $$ \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+\mathrm{CO}(g) \longrightarrow \mathrm{Fe}(s)+\mathrm{CO}_{2}(g) $$ (a) Balance this equation. (b) Calculate the number of grams of CO that can react with 0.350 \(\mathrm{kg}\) of \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) . (c) Calculate the number of grams of Fe and the number of grams of \(\mathrm{CO}_{2}\) formed when 0.350 \(\mathrm{kg}\) of \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) reacts. (d) Show that your calculations in parts (b) and (c) are consistent with the law of conservation of mass.

Aluminum sulfide reacts with water to form aluminum hydroxide and hydrogen sulfide. (a) Write the balanced chemical equation for this reaction. (b) How many grams of aluminum hydroxide are obtained from 14.2 \(\mathrm{g}\) of aluminum sulfide?

Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas. (a) Write a balanced chemical equation for the reaction. (b) How many grams of calcium hydride are needed to form 4.500 g of hydrogen?