Chapter 3

Methanol, \(\mathrm{CH}_{3} \mathrm{OH},\) is a clean-burning, easily handled fuel. It can be made by the direct reaction of \(\mathrm{CO}\) and \(\mathrm{H}_{2}\). $$\mathrm{CO}(\mathrm{g})+2 \mathrm{H}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CH}_{3} \mathrm{OH}(\ell)$$ (a) For a mixture of \(12.0 \mathrm{~g} \mathrm{H}_{2}\) and \(74.5 \mathrm{~g} \mathrm{CO},\) determine the limiting reactant. (b) Calculate the mass (g) of the excess reactant left after reaction is complete. (c) Calculate the theoretical mass of methanol that can be obtained.

This reaction can be used to generate hydrogen gas from methane: $$\mathrm{CH}_{4}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \longrightarrow \mathrm{CO}(\mathrm{g})+3 \mathrm{H}_{2}(\mathrm{~g})$$ If you use \(500 . \mathrm{g} \mathrm{CH}_{4}\) and \(1300 . \mathrm{g}\) water: (a) Determine the limiting reactant. (b) Calculate the mass (g) of \(\mathrm{H}_{2}\) that can be produced. (c) Calculate the mass (g) of the excess reactant remaining when the reaction is complete.

Aspirin is produced by the reaction of salicylic acid and acetic anhydride. $$\begin{array}{cc}2 \mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{3}(\mathrm{~s})+\mathrm{C}_{4} \mathrm{H}_{6}\mathrm{O}_{3}(\ell) \longrightarrow 2 \mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\ell) \\\\\begin{array}{c} \text { salicylic } \\\\\text { acid }\end{array} & \begin{array}{c} \text { acetic } \\\\\text { anhydride }\end{array} & \text { aspirin }\end{array}$$ If you mix \(100 . \mathrm{g}\) of each of the reactants, calculate the maximum mass of aspirin that can be obtained.

Iron oxide can be reduced to the metal as follows: $$\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})+3 \mathrm{CO}(\mathrm{g}) \longrightarrow 2 \mathrm{Fe}(\mathrm{s})+3 \mathrm{CO}_{2}(\mathrm{~g})$$ Calculate the mass of iron that can be obtained from \(1.00 \mathrm{~kg}\) of the iron oxide. If \(654 \mathrm{~g}\) Fe was obtained from the reaction, calculate the percent yield.

Quicklime, \(\mathrm{CaO},\) is formed when calcium hydroxide is heated. $$\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{~s}) \longrightarrow \mathrm{CaO}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell)$$ The theoretical yield is \(65.5 \mathrm{~g}\) but only \(36.7 \mathrm{~g}\) quicklime is produced. Calculate the percent yield.

Diborane, \(\mathrm{B}_{2} \mathrm{H}_{6}\), is valuable for the synthesis of new organic compounds. The boron compound can be made by the reaction $$2 \mathrm{NaBH}_{4}(\mathrm{~s})+\mathrm{I}_{2}(\mathrm{~s}) \longrightarrow \mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{~g})+2 \mathrm{NaI}(\mathrm{s})+\mathrm{H}_{2}(\mathrm{~g})$$ Suppose you use \(1.203 \mathrm{~g} \mathrm{NaBH}_{4}\) and excess iodine, and you isolate \(0.295 \mathrm{~g} \mathrm{~B}_{2} \mathrm{H}_{6} .\) Calculate the percent yield of \(\mathrm{B}_{2} \mathrm{H}_{6}\)

Disulfur dichloride, which has a revolting smell, can be prepared by directly combining \(\mathrm{S}_{8}\) and \(\mathrm{Cl}_{2}\), but it can also be made by this reaction: \(3 \mathrm{SCl}_{2}(\ell)+4 \mathrm{NaF}(\mathrm{s}) \longrightarrow \mathrm{SF}_{4}(\mathrm{~g})+\mathrm{S}_{2} \mathrm{Cl}_{2}(\ell)+4 \mathrm{NaCl}(\mathrm{s})\) Calculate the mass of \(\mathrm{SCl}_{2}\) needed to react with excess NaF to prepare \(1.19 \mathrm{~g} \mathrm{~S}_{2} \mathrm{Cl}_{2}\) if the expected yield is \(51 \%\).

The ceramic silicon nitride, \(\mathrm{Si}_{3} \mathrm{~N}_{4}\), is made by heating silicon and nitrogen at an elevated temperature. $$3 \mathrm{Si}(\mathrm{s})+2 \mathrm{~N}_{2}(\mathrm{~g}) \longrightarrow \mathrm{Si}_{3} \mathrm{~N}_{4}(\mathrm{~s})$$ Calculate the mass of silicon that must combine with excess \(\mathrm{N}_{2}\) to produce \(1.0 \mathrm{~kg} \mathrm{Si}_{3} \mathrm{~N}_{4}\) if this process is \(92 \%\) efficient.

Propionic acid, an organic acid, contains only \(\mathrm{C}, \mathrm{H},\) and O. When \(0.236 \mathrm{~g}\) of the acid burns completely in \(\mathrm{O}_{2}\) it gives \(0.421 \mathrm{~g} \mathrm{CO}_{2}\) and \(0.172 \mathrm{~g} \mathrm{H}_{2} \mathrm{O} .\) Determine the empirical formula of the acid.

Quinone, which is used in the dye industry and in chemical photography, is an organic compound containing only \(\mathrm{C}, \mathrm{H},\) and \(\mathrm{O} .\) Determine the empirical formula if \(0.105 \mathrm{~g}\) of the compound gives \(0.257 \mathrm{~g} \mathrm{CO}_{2}\) and \(0.0350 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}\) when burned completely.

L-Dopa is a drug used for the treatment of Parkinson's disease. Elemental analysis shows it to be \(54.82 \%\) carbon, \(7.10 \%\) nitrogen, \(32.46 \%\) oxygen, and the remainder hydrogen. (a) Determine \(\mathrm{L}\) -dopa's empirical formula. (b) The molar mass of \(\mathrm{L}\) -dopa is \(197.19 \mathrm{~g} / \mathrm{mol}\). Determine its molecular formula.

Write the balanced chemical equation for the complete combustion of adipic acid, an organic acid containing \(49.31 \% \mathrm{C}, 6.90 \% \mathrm{H},\) and the remainder \(\mathrm{O},\) by mass.

Assume that \(6.73 \mathrm{~g} \mathrm{Na}_{2} \mathrm{CO}_{3}\) is dissolved in enough water to make \(250 . \mathrm{mL}\) solution. (a) Calculate the molarity of the sodium carbonate. (b) Calculate the concentrations of the \(\mathrm{Na}^{+}\) and \(\mathrm{CO}_{3}^{2-}\) ions.

Some \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7},\) with a mass of \(2.335 \mathrm{~g},\) is dissolved in enough water to make \(500 . \mathrm{mL}\) solution. (a) Calculate the molarity of the potassium dichromate. (b) Calculate the concentrations of the \(\mathrm{K}^{+}\) and \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\) ions.

Calculate the volume of 0.123 -M \(\mathrm{NaOH}\) that contains \(25.0 \mathrm{~g} \mathrm{NaOH}\). Express your result in milliliters.

Calculate the volume of \(2.06-\mathrm{M} \mathrm{KMnO}_{4}\) that contains \(322 \mathrm{~g}\) solute.

You need \(1.00 \mathrm{~L}\) of \(0.125-\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\). Which method is best to prepare this solution? Explain your choice. (a) Dilute \(36.0 \mathrm{~mL}\) of \(1.25-\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) to a volume of \(1.00 \mathrm{~L}\). (b) Dilute \(20.8 \mathrm{~mL}\) of \(6.00-\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) to a volume of \(1.00 \mathrm{~L}\). (c) Add \(50.0 \mathrm{~mL}\) of \(3.00-\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) to \(950 . \mathrm{mL}\) water. (d) Add 500. mL of \(0.500-\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) to \(500 . \mathrm{mL}\) water.

You need \(300 . \mathrm{mL}\) of \(0.500-\mathrm{M} \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} .\) Which method is best to prepare this solution? Explain your choice. (a) Dilute \(250 . \mathrm{mL}\) of \(0.600-\mathrm{M} \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) to \(300 . \mathrm{mL}\). (b) Add \(50.0 \mathrm{~mL}\) water to \(250 . \mathrm{mL}\) of \(0.250-\mathrm{M} \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (c) Dilute \(125 \mathrm{~mL}\) of \(1.00-\mathrm{M} \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) to \(300 . \mathrm{mL}\). (d) Add \(30.0 \mathrm{~mL}\) of \(1.50-\mathrm{M} \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) to \(270 . \mathrm{mL}\) of water.

You need to make a \(0.300-\mathrm{M}\) solution of \(\mathrm{NiSO}_{4}(\mathrm{aq}) . \mathrm{Cal}-\) culate the mass of \(\mathrm{NiSO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) you should put into a 0.500-L volumetric flask.

You wish to make a \(0.200-\mathrm{M}\) solution of \(\mathrm{CuSO}_{4}(\mathrm{aq})\). Calculate the mass of \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\) required to make \(0.500 \mathrm{~L}\) of solution.

Calculate the volume, in milliliters, of \(0.125-\mathrm{M} \mathrm{HNO}_{3}\) required to react completely with \(1.30 \mathrm{~g} \mathrm{Ba}(\mathrm{OH})_{2}\). \(2 \mathrm{HNO}_{3}(\mathrm{aq})+\mathrm{Ba}(\mathrm{OH})_{2}(\mathrm{~s}) \longrightarrow \mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)\)

Diborane, \(\mathrm{B}_{2} \mathrm{H}_{6},\) can be produced by this reaction: \(2 \mathrm{NaBH}_{4}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow\) \(2 \mathrm{H}_{2}(\mathrm{~g})+\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{~g})\) Calculate the volume, in milliliters, of \(0.0875-\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) needed to completely react with \(1.35 \mathrm{~g} \mathrm{NaBH}_{4}\)..

You mix \(25.0 \mathrm{~mL}\) of \(0.234-\mathrm{M} \mathrm{FeCl}_{3}\) solution with \(42.5 \mathrm{~mL}\) of \(0.453-\mathrm{M} \mathrm{NaOH}\) (a) Calculate the maximum mass, in grams, of \(\mathrm{Fe}(\mathrm{OH})_{3}\) that will precipitate. (b) Determine which reactant is in excess. (c) Calculate the concentration of the excess reactant remaining in solution after the maximum mass of \(\mathrm{Fe}(\mathrm{OH})_{3}\) has precipitated.

A sample of a mixture of oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4},\) and sodium chloride, \(\mathrm{NaCl}\), has a mass of \(4.554 \mathrm{~g}\). If a volume of \(29.58 \mathrm{~mL}\) of \(0.550-\mathrm{M} \mathrm{NaOH}\) is required to neutralize all the \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4},\) calculate the mass percent of oxalic acid in the mixture. Oxalic acid and \(\mathrm{NaOH}\) react according to this equation: $$\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+2 \mathrm{NaOH}(\mathrm{aq}) \longrightarrow \mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$

Potassium hydrogen phthalate, \(\mathrm{KHC}_{8} \mathrm{H}_{4} \mathrm{O}_{4},\) is used to standardize solutions of bases. The acidic anion reacts with bases according to this net ionic equation: $$\mathrm{HC}_{8} \mathrm{H}_{4} \mathrm{O}_{4}^{-}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq}) \longrightarrow \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{C}_{8} \mathrm{H}_{4} \mathrm{O}_{4}^{2-}(\mathrm{aq})$$ A \(0.902-g\) sample of potassium hydrogen phthalate requires \(26.45 \mathrm{~mL} \mathrm{NaOH}\) to react; determine the molarity of the \(\mathrm{NaOH}\).

You are given \(0.954 \mathrm{~g}\) of an unknown acid, \(\mathrm{H}_{2} \mathrm{~A},\) which reacts with \(\mathrm{NaOH}\) according to the balanced equation $$\mathrm{H}_{2} \mathrm{~A}(\mathrm{aq})+2 \mathrm{NaOH}(\mathrm{aq}) \longrightarrow \mathrm{Na}_{2} \mathrm{~A}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$ If \(36.04 \mathrm{~mL}\) of \(0.509-\mathrm{M} \mathrm{NaOH}\) is required to react with all of the acid, calculate the molar mass of the acid.

In an experiment, \(1.056 \mathrm{~g}\) of a metal carbonate containing an unknown metal \(\mathrm{M}\) was heated to give the metal oxide and \(0.376 \mathrm{~g} \mathrm{CO}_{2}\) $$\mathrm{MCO}_{3}(\mathrm{~s}) \longrightarrow \mathrm{MO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g})$$ Determine the identity of the metal \(\mathrm{M}\). (a) \(\mathrm{Ni}\) (b) \(\mathrm{Cu}\) (c) Co (d) \(\mathrm{Ba}\)

Uranium(VI) oxide reacts with bromine trifluoride to give uranium(IV) fluoride, an important step in the purification of uranium ore. \(6 \mathrm{UO}_{3}(\mathrm{~s})+8 \mathrm{BrF}_{3}(\ell) \longrightarrow 6 \mathrm{UF}_{4}(\mathrm{~s})+4 \mathrm{Br}_{2}(\ell)+9 \mathrm{O}_{2}(\mathrm{~g})\) You begin with \(365 \mathrm{~g}\) each of \(\mathrm{UO}_{3}\) and \(\mathrm{BrF}_{3}\); determine the maximum yield, in grams, of \(\mathrm{UF}_{4}\).

Silicon and hydrogen form a series of interesting compounds, \(\mathrm{Si}_{x} \mathrm{H}_{y}\). To find the formula of one of them, a \(6.22-\mathrm{g}\) sample of the compound is burned in oxygen. All of the \(\mathrm{Si}\) is converted to \(11.64 \mathrm{~g} \mathrm{SiO}_{2}\) and all of the \(\mathrm{H}\) to \(6.980 \mathrm{~g} \mathrm{H}_{2} \mathrm{O} .\) Determine the empirical formula of the silicon compound.

Boron forms an extensive series of compounds with hydrogen, all with the general formula \(\mathrm{B}_{x} \mathrm{H}_{y}\). To analyze one of these compounds, you burn it in air and isolate the boron in the form of \(\mathrm{B}_{2} \mathrm{O}_{3}\) and the hydrogen in the form of water. You find that \(0.1482 \mathrm{~g} \mathrm{~B}_{x} \mathrm{H}_{y}\) gives \(0.4221 \mathrm{~g}\) \(\mathrm{B}_{2} \mathrm{O}_{3}\) when burned in excess \(\mathrm{O}_{2} .\) Determine the empirical formula of \(\mathrm{B}_{x} \mathrm{H}_{y}\)

The Hargreaves process is an industrial method for making sodium sulfate for use in papermaking. $$4 \mathrm{NaCl}+2 \mathrm{SO}_{2}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2} \longrightarrow 2 \mathrm{Na}_{2} \mathrm{SO}_{4}+4 \mathrm{HCl}$$ (a) If you start with \(10 .\) mol of each reactant, determine which one limits the amount of \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) produced. (b) Determine the amount of \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) produced if you start with \(100 . \mathrm{g}\) of each reactant.

Hydrogen sulfide gas is bubbled into an acidified solution of potassium permanganate; elemental sulfur precipitates. The unbalanced equation is \(\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})+\mathrm{MnO}_{4}^{-}(\mathrm{aq})+\mathrm{H}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{S}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell)\) (a) Potassium ions are not given in the equation. Explain why. (b) Explain why this is a redox equation. (c) Identify the oxidizing and reducing agents.

An aqueous hydrochloric acid solution is \(37.0 \% \mathrm{HCl}\) by mass. The density of the solution is \(1.185 \mathrm{~g} / \mathrm{mL}\). Calculate the molarity of \(\mathrm{HCl}\) in this solution.

Azurite is a copper-containing mineral that often forms beautiful crystals. Its formula is \(\mathrm{Cu}_{3}\left(\mathrm{CO}_{3}\right)_{2}(\mathrm{OH})_{2} .\) Write a balanced equation for the reaction of this mineral with hydrochloric acid.

Determine which of these are redox reactions, which are acid-base reactions, and which are gas-forming reactions. Identify the oxidizing and reducing agents in each of the redox reactions. Identify the acid and base in each acidbase reaction. (a) \(\mathrm{NaOH}(\mathrm{aq})+\mathrm{H}_{3} \mathrm{PO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{NaH}_{2} \mathrm{PO}_{4}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)\) (b) \(\mathrm{NH}_{3}(\mathrm{~g})+\mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{NH}_{4} \mathrm{HCO}_{3}(\mathrm{aq})\) (c) \(\mathrm{TiCl}_{4}(\mathrm{~g})+2 \mathrm{Mg}(\ell) \longrightarrow \mathrm{Ti}(\mathrm{s})+2 \mathrm{MgCl}_{2}(\ell)\) (d) \(\mathrm{NaCl}(\mathrm{s})+\mathrm{NaHSO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{HCl}(\mathrm{g})+\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})\)

Chlorofluorocarbons are involved in creating the hole in the ozone layer. Their manufacture begins with the preparation of HF from the mineral fluorspar, \(\mathrm{CaF}_{2},\) according to this unbalanced equation: $$\mathrm{CaF}_{2}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{HF}(\mathrm{g})+\mathrm{CaSO}_{4}(\mathrm{~s})$$ HF is combined with, for example, \(\mathrm{CCl}_{4}\) in the presence of \(\mathrm{SbCl}_{5}\) to make \(\mathrm{CCl}_{2} \mathrm{~F}_{2},\) called dichlorodifluoromethane or CFC-12, and other chlorofluorocarbons. $$2 \mathrm{HF}(\mathrm{g})+\mathrm{CCl}_{4}(\ell) \longrightarrow \mathrm{CCl}_{2} \mathrm{~F}_{2}(\mathrm{~g})+2 \mathrm{HCl}(\mathrm{g})$$ (a) Balance the first equation and name each substance. (b) Is the first reaction best classified as an acid-base reaction, an oxidation-reduction reaction, or a precipitation reaction? (c) Give the names of the compounds \(\mathrm{CCl}_{4}, \mathrm{SbCl}_{5},\) and \(\mathrm{HCl}\). (d) Another chlorofluorocarbon produced in the reaction is composed of \(8.74 \% \mathrm{C}, 77.43 \% \mathrm{Cl}\), and \(13.83 \% \mathrm{~F}\). Determine the empirical formula of the compound.

Vitamin \(\mathrm{C}\) is ascorbic acid, \(\mathrm{HC}_{6} \mathrm{H}_{7} \mathrm{O}_{6},\) which can be titrated with a strong base. \(\mathrm{HC}_{6} \mathrm{H}_{7} \mathrm{O}_{6}(\mathrm{aq})+\mathrm{NaOH}(\mathrm{aq}) \longrightarrow \mathrm{NaC}_{6} \mathrm{H}_{7} \mathrm{O}_{6}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)\) A student dissolved a \(500.0-\mathrm{mg}\) vitamin \(\mathrm{C}\) tablet in \(200.0 \mathrm{~mL}\) water and then titrated it with 0.1250 -M \(\mathrm{NaOH}\). It required \(21.30 \mathrm{~mL}\) of the base to reach the equivalence point. Calculate the mass percentage of the tablet that is impurity.

You are given an acid and told only that it could be citric acid (molar mass \(=192.1 \mathrm{~g} / \mathrm{mol}\) ) or tartaric acid (molar mass \(=150.1 \mathrm{~g} / \mathrm{mol}\) ). To determine which acid you have, you react it with \(\mathrm{NaOH}\). The appropriate reactions are Citric acid: \(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}(\mathrm{aq})+3 \mathrm{NaOH}(\mathrm{aq}) \longrightarrow\) $$\mathrm{Na}_{3} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}_{7}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\ell)$$ Tartaric acid: \(\mathrm{C}_{4} \mathrm{H}_{6} \mathrm{O}_{6}(\mathrm{aq})+2 \mathrm{NaOH}(\mathrm{aq}) \longrightarrow\) $$\mathrm{Na}_{2} \mathrm{C}_{4} \mathrm{H}_{4} \mathrm{O}_{6}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$ You find that a \(0.956-\mathrm{g}\) sample requires \(29.1 \mathrm{~mL}\) of \(0.513-\mathrm{M} \mathrm{NaOH}\) to reach the equivalence point. Determine which is the unknown acid.

In the past, devices for testing a driver's breath for alcohol depended on this reaction: $$\begin{array}{r} 3 \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{aq})+2 \mathrm{~K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{aq})+8 \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \\ 3 \mathrm{CH}_{3} \mathrm{COOH}(\mathrm{aq})+2 \mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}(\mathrm{aq})+ \\ 2 \mathrm{~K}_{2} \mathrm{SO}_{4}(\mathrm{aq})+11 \mathrm{H}_{2} \mathrm{O}(\ell) \end{array}$$ (a) Write the net ionic equation for this reaction. (b) What oxidation numbers are changing in the course of this reaction? (c) Which substances are being oxidized and reduced? (d) Which substance is the oxidizing agent and which is the reducing agent?

The salt calcium sulfate is sparingly soluble in water with a solubility of \(0.209 \mathrm{~g} / 100 \mathrm{~mL}\) water at \(30^{\circ} \mathrm{C}\). If you stirred \(0.550 \mathrm{~g} \mathrm{CaSO}_{4}\) into \(100.0 \mathrm{~mL}\) water at \(30^{\circ} \mathrm{C}\) calculate the molarity of the resulting solution. Calculate the mass of \(\mathrm{CaSO}_{4}\) that would remain undissolved.

When these pairs of reactants are combined in a beaker, (a) describe in words what the contents of the beaker would look like before and after any reaction occurs; (b) use different circles for atoms, molecules, and ions to draw a nanoscale (particulate-level) diagram of what the contents would look like; and (c) write a chemical equation to represent symbolically what the contents would look like. \(\mathrm{LiCl}(\mathrm{aq})\) and \(\mathrm{AgNO}_{3}(\mathrm{aq})\) \(\mathrm{NaOH}(\mathrm{aq})\) and \(\mathrm{HCl}(\mathrm{aq})\)

Chemical equations can be interpreted on either a nanoscale level (atoms, molecules, ions) or a mole level (moles of reactants and products). Write word statements to describe the combustion of butane on a nanoscale level and a mole level. $$2 \mathrm{C}_{4} \mathrm{H}_{10}(\mathrm{~g})+13 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 8 \mathrm{CO}_{2}(\mathrm{~g})+10 \mathrm{H}_{2} \mathrm{O}(\ell)$$

If 1.5 mol Cu reacts with a solution containing 4.0 mol \(\mathrm{AgNO}_{3},\) what ions will be present in the solution at the end of the reaction? $$\mathrm{Cu}(\mathrm{s})+2 \mathrm{AgNO}_{3}(\mathrm{aq}) \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{Ag}(\mathrm{s})$$

Explain how you could prepare barium sulfate by (a) an acid-base reaction, (b) a precipitation reaction, and (c) a gas-forming reaction. The materials you have to start with are \(\mathrm{BaCO}_{3}, \mathrm{Ba}(\mathrm{OH})_{2}, \mathrm{Na}_{2} \mathrm{SO}_{4},\) and \(\mathrm{H}_{2} \mathrm{SO}_{4}\) .

Students were asked to prepare nickel sulfate by reacting a nickel compound with a sulfate compound in water and then evaporating the water. Three students chose these pairs of reactants: $$\begin{array}{ll} \hline \text { Student } 1 & \mathrm{Ni}(\mathrm{OH})_{2} \text { and } \mathrm{H}_{2} \mathrm{SO}_{4} \\ \text { Student } 2 & \mathrm{Ni}\left(\mathrm{NO}_{3}\right)_{2} \text { and } \mathrm{Na}_{2} \mathrm{SO}_{4} \\ \text { Student } 3 & \mathrm{NiCO}_{3} \text { and } \mathrm{H}_{2} \mathrm{SO}_{4} \\ \hline\end{array}$$ Comment on each student's choice of reactants and how successful you think each student will be at preparing nickel sulfate by the procedure indicated.

An unknown solution contains either lead ions or barium ions, but not both. Which one of these solutions could you use to tell whether the ions present are \(\mathrm{Pb}^{2+}\) or \(\mathrm{Ba}^{2+}\) ? Explain the reasoning behind your choice. $$\mathrm{HCl}(\mathrm{aq}), \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}), \mathrm{H}_{3} \mathrm{PO}_{4}(\mathrm{aq})$$

An unknown solution contains either calcium ions or strontium ions, but not both. Which one of these solutions could you use to tell whether the ions present are \(\mathrm{Ca}^{2+}\) or \(\mathrm{Sr}^{2+}\) ? Explain the reasoning behind your choice. $$\mathrm{NaOH}(\mathrm{aq}), \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}), \mathrm{H}_{2} \mathrm{~S}(\mathrm{aq})$$

A chemical company was interested in characterizing a competitor's organic acid (it consists of \(\mathrm{C}, \mathrm{H},\) and \(\mathrm{O})\). After determining that it was a diacid, \(\mathrm{H}_{2} \mathrm{X},\) a \(0.1235-\mathrm{g}\) sample was neutralized with \(15.55 \mathrm{~mL}\) of \(0.1087-\mathrm{M}\) \(\mathrm{NaOH}\). Next, a \(0.3469-\mathrm{g}\) sample was burned completely in pure oxygen, producing \(0.6268 \mathrm{~g} \mathrm{CO}_{2}\) and \(0.2138 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}\). (a) Calculate the molar mass of \(\mathrm{H}_{2} \mathrm{X}\). (b) Calculate the empirical formula for the diacid. (c) Calculate the molecular formula for the diacid.

Hydrogen gas \(\mathrm{H}_{2}(\mathrm{~g})\) is reacted with a sample of \(\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})\) at \(400^{\circ} \mathrm{C}\). Two products are formed: water vapor and a black solid compound that is \(72.3 \% \mathrm{Fe}\) and \(27.7 \% \mathrm{O}\) by mass. Write the balanced chemical equation for the reaction.

In a reaction, \(1.2 \mathrm{~g}\) element A reacts with exactly \(3.2 \mathrm{~g}\) oxygen to form an oxide, \(\mathrm{AO}_{x} ; 2.4 \mathrm{~g}\) element A reacts with exactly \(3.2 \mathrm{~g}\) oxygen to form a second oxide, \(\mathrm{AO}_{y}\) (a) Determine the ratio \(x: y\). (b) If \(x=2\), determine what the identity of element A might be.