Chapter 3

Ereon is a trade name for a group of gaseous compounds once used as propellants in aerosol cans. Which has a higher percentage of chlorine: Freon-12 \(\left(\mathrm{CCl}_{2} \mathrm{~F}_{2}\right)\) or Freon-141b \(\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}_{2} \mathrm{~F}\right) ?\)

Which has a higher percentage of fluorine: Freon-12 \(\left(\mathrm{CCl}_{2} \mathrm{~F}_{2}\right)\) or Freon \(113\left(\mathrm{C}_{2} \mathrm{Cl}_{3} \mathrm{~F}_{3}\right) ?\)

It was found that \(2.35 \mathrm{~g}\) of a compound of phosphorus and chlorine contained \(0.539 \mathrm{~g}\) of phosphorus. What are the percentages by mass of phosphorus and chlorine in this compound?

An analysis revealed that \(5.67 \mathrm{~g}\) of a compound of nitrogen and oxygen contained \(1.47 \mathrm{~g}\) of nitrogen. What are the percentages by mass of nitrogen and oxygen in this compound?

Phencyclidine ("angel dust") is \(\mathrm{C}_{17} \mathrm{H}_{25} \mathrm{~N}\). A sample suspected of being this illicit drug was found to have a percentage composition of \(84.71 \% \mathrm{C}, 10.42 \% \mathrm{H},\) and \(5.61 \% \mathrm{~N}\). Do these data acceptably match the theoretical data for phencyclidine?

The hallucinogenic drug LSD has the molecular formula \(\mathrm{C}_{20} \mathrm{H}_{25} \mathrm{~N}_{3} \mathrm{O} .\) One suspected sample contained \(74.07 \% \mathrm{C},\) \(7.95 \% \mathrm{H},\) and \(9.99 \% \mathrm{~N}\) (a) What is the percentage of \(\mathrm{O}\) in the sample? (b) Are these data consistent for \(L S D ?\)

How many grams of \(\mathrm{O}\) are combined with \(7.14 \times 10^{21}\) atoms of \(\mathrm{N}\) in the compound dinitrogen pentoxide?

How many grams of \(\mathrm{C}\) are combined with \(4.25 \times 10^{23}\) atoms of \(\mathrm{H}\) in the compound \(\mathrm{C}_{5} \mathrm{H}_{12} ?\)

Write empirical formulas for the following compounds. (a) \(\mathrm{S}_{2} \mathrm{Cl}_{2}\) (d) \(\mathrm{As}_{2} \mathrm{O}_{6}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) (e) \(\mathrm{H}_{2} \mathrm{O}_{2}\) (c) \(\mathrm{NH}_{3}\)

What are the empirical formulas of the following compounds? (a) \(\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{OH})_{2}\) (d) \(\mathrm{B}_{2} \mathrm{H}_{6}\) (b) \(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{8}\) (e) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (c) \(\mathrm{C}_{4} \mathrm{H}_{10}\)

A sample of Freon was found to contain \(0.423 \mathrm{~g}\) of \(\mathrm{C}\), \(2.50 \mathrm{~g}\) of \(\mathrm{Cl}\), and \(1.34 \mathrm{~g}\) of \(\mathrm{F}\). What is the empirical formula of this compound?

Cinnamic acid, a compound related to the flavor component of cinnamon, is \(72.96 \%\) carbon, \(5.40 \%\) hydrogen, and the rest is oxygen. What is the empirical formula of this acid?

A dry-cleaning fluid composed of only carbon and chlorine was found to be composed of \(14.5 \% \mathrm{C}\) and \(85.5 \% \mathrm{Cl}\) (by mass). What is the empirical formula of this compound?

One compound of mercury with a molar mass of 519 contains \(77.26 \% \mathrm{Hg}, 9.25 \% \mathrm{C},\) and \(1.17 \% \mathrm{H}\) (with the balance being \(\mathrm{O}\) ). Calculate the empirical formula.

When \(0.684 \mathrm{~g}\) of an organic compound containing only carbon, hydrogen, and oxygen was burned in oxygen, \(1.312 \mathrm{~g}\) of \(\mathrm{CO}_{2}\) and \(0.805 \mathrm{~g}\) of \(\mathrm{H}_{2} \mathrm{O}\) were obtained. What is the empirical formula of the compound?

The following are empirical formulas and the masses per mole for three compounds. What are their molecular formulas? (a) \(\mathrm{NaS}_{2} \mathrm{O}_{3} ; 270.4 \mathrm{~g} / \mathrm{mol}\) (c) \(\mathrm{C}_{2} \mathrm{HCl} ; 181.4 \mathrm{~g} / \mathrm{mol}\) (b) \(\mathrm{C}_{3} \mathrm{H}_{2} \mathrm{Cl} ; 147.0 \mathrm{~g} / \mathrm{mol}\)

Balance the following equations. (a) \(\mathrm{CaO}+\mathrm{HNO}_{3} \longrightarrow \mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2} \longrightarrow \mathrm{MgCO}_{3}+\mathrm{NaNO}_{3}\) (c) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}+\mathrm{NaOH} \longrightarrow\) \(\mathrm{Na}_{3} \mathrm{PO}_{4}+\mathrm{NH}_{3}+\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{LiHCO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{Li}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2}\) (e) \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\)

Write the equation that expresses in acceptable chemical shorthand the following statement: "Iron can be made to react with molecular oxygen to give iron(III) oxide."

The conversion of one air pollutant, nitrogen monoxide, produced in vehicle engines, into another pollutant, nitrogen dioxide, occurs when nitrogen monoxide reacts with molecular oxygen in the air. Write the balanced equation for this reaction.

A balanced chemical equation contains the term \(“ 2 \mathrm{Ba}(\mathrm{OH})_{2} \cdot 8 \mathrm{H}_{2} \mathrm{O} .\) " How many atoms of each element does this represent in the molecular view? How many moles of each element does this represent on the laboratory scale?

A balanced chemical equation contains the term \(" 3 \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\)." How many atoms of each element does this represent in the molecular view? How many moles of each element does this represent on the laboratory scale?

Chlorine is used by textile manufacturers to bleach cloth. Excess chlorine is destroyed by its reaction with sodium thiosulfate, \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\), as follows. $$ \begin{aligned} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}(a q)+4 \mathrm{Cl}_{2}(g)+5 \mathrm{H}_{2} \mathrm{O} \longrightarrow \\ 2 \mathrm{NaHSO}_{4}(a q)+8 \mathrm{HCl}(a q) \end{aligned} $$ (a) How many moles of \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) are needed to react with \(0.12 \mathrm{~mol}\) of \(\mathrm{Cl}_{2}\) ? (b) How many moles of \(\mathrm{HCl}\) can form from \(0.12 \mathrm{~mol}\) of \(\mathrm{Cl}_{2} ?\) (c) How many moles of \(\mathrm{H}_{2} \mathrm{O}\) are required for the reaction $$ \text { of } 0.12 \mathrm{~mol} \text { of } \mathrm{Cl}_{2} ? $$ (d) How many moles of \(\mathrm{H}_{2} \mathrm{O}\) react if \(0.24 \mathrm{~mol} \mathrm{HCl}\) is formed?

The octane in gasoline burns according to the following equation. $$ 2 \mathrm{C}_{8} \mathrm{H}_{18}+25 \mathrm{O}_{2} \longrightarrow 16 \mathrm{CO}_{2}+18 \mathrm{H}_{2} \mathrm{O} $$ (a) How many moles of \(\mathrm{O}_{2}\) are needed to react fully with \(6.84 \mathrm{~mol}\) of octane? (b) How many moles of \(\mathrm{CO}_{2}\) can be formed from 0.511 mol of octane? (c) How many moles of water are produced by the combustion of \(8.20 \mathrm{~mol}\) of octane? (d) If this reaction is used to synthesize \(6.00 \mathrm{~mol}\) of \(\mathrm{CO}_{2}\), how many moles of oxygen are needed? How many moles of octane?

Propane burns according to the following equation: $$ \mathrm{C}_{3} \mathrm{H}_{8}+5 \mathrm{O}_{2} \longrightarrow 3 \mathrm{CO}_{2}+4 \mathrm{H}_{2} \mathrm{O} $$ (a) How many grams of \(\mathrm{O}_{2}\) are needed to react fully with \(3.45 \mathrm{~mol}\) of propane? (b) How many grams of \(\mathrm{CO}_{2}\) can form from \(0.177 \mathrm{~mol}\) of propane? (c) How many grams of water are produced by the combustion of \(4.86 \mathrm{~mol}\) of propane?

The following reaction is used to extract gold from pre-treated gold ore: \(2 \mathrm{Au}(\mathrm{CN})_{2}^{-}(a q)+\mathrm{Zn}(s) \longrightarrow 2 \mathrm{Au}(s)+\mathrm{Zn}(\mathrm{CN})_{4}^{-}(a q)\) (a) How many grams of \(Z n\) are needed to react with 0.11 mol of \(\mathrm{Au}(\mathrm{CN})_{2}^{-} ?\) (b) How many grams of Au can form from \(0.11 \mathrm{~mol}\) of \(\mathrm{Au}(\mathrm{CN})_{2}^{-} ?\) (c) How many grams of \(\mathrm{Au}(\mathrm{CN})_{2}^{-}\) are required for the reaction of \(0.11 \mathrm{~mol}\) of \(\mathrm{Zn}\) ?

The incandescent white of a fireworks display is caused by the reaction of phosphorus with \(\mathrm{O}_{2}\) to give \(\mathrm{P}_{4} \mathrm{O}_{10}\). (a) Write the balanced chemical equation for the reaction. (b) How many grams of \(\mathrm{O}_{2}\) are needed to combine with \(6.85 \mathrm{~g}\) of \(\mathrm{P} ?\) (c) How many grams of \(\mathrm{P}_{4} \mathrm{O}_{10}\) can be made from \(8.00 \mathrm{~g}\) of \(\mathrm{O}_{2} ?\) (d) How many grams of \(\mathrm{P}\) are needed to make \(7.46 \mathrm{~g}\) of \(\mathrm{P}_{4} \mathrm{O}_{10} ?\)

The reaction of hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4},\) with hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2},\) has been used in rocket engines. One way these compounds react is described by the equation $$ \mathrm{N}_{2} \mathrm{H}_{4}+7 \mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow 2 \mathrm{HNO}_{3}+8 \mathrm{H}_{2} \mathrm{O} $$ According to this equation, how many grams of \(\mathrm{H}_{2} \mathrm{O}_{2}\) are needed to react completely with \(852 \mathrm{~g}\) of \(\mathrm{N}_{2} \mathrm{H}_{4} ?\)

Oxygen gas can be produced in the laboratory by decomposition of potassium chlorate \(\left(\mathrm{KClO}_{3}\right)\) $$ \mathrm{KClO}_{3}(s) \longrightarrow 2 \mathrm{KCl}(s)+3 \mathrm{O}_{2}(g) $$ How many \(\mathrm{kg}\) of \(\mathrm{O}_{2}\) can be produced from \(1.0 \mathrm{~kg}\) of \(\mathrm{KClO}_{3} ?\)

Some of the acid in acid rain is produced by the following reaction: $$ 3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g) $$ If a falling raindrop weighing \(0.050 \mathrm{~g}\) comes into contact with \(1.0 \mathrm{mg}\) of \(\mathrm{NO}_{2}(g)\), how many milligrams of \(\mathrm{HNO}_{3}\) can be produced?

Barium sulfate, \(\mathrm{BaSO}_{4}\), is made by the following reaction. \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{Na}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{BaSO}_{4}(s)+2 \mathrm{NaNO}_{3}(a q)\) An experiment was begun with \(75.00 \mathrm{~g}\) of \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\) and an excess of \(\mathrm{Na}_{2} \mathrm{SO}_{4}\). After collecting and drying the product, \(64.45 \mathrm{~g}\) of \(\mathrm{BaSO}_{4}\) was obtained. Calculate the theoretical yield and percentage yield of \(\mathrm{BaSO}_{4}\)

Aluminum sulfate can be made by the following reaction. \(2 \mathrm{AlCl}_{3}(a q)+3 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}(a q)+6 \mathrm{HCl}(a q)\) It is quite soluble in water, so to isolate it the solution has to be evaporated to dryness. This drives off the volatile \(\mathrm{HCl},\) but the residual solid has to be heated to a little over \(200^{\circ} \mathrm{C}\) to drive off all of the water. In one experiment, \(25.0 \mathrm{~g}\) of \(\mathrm{AlCl}_{3}\) was mixed with \(30.0 \mathrm{~g}\) of \(\mathrm{H}_{2} \mathrm{SO}_{4}\). Eventually, \(28.46 \mathrm{~g}\) of pure \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) was isolated. Calculate the percentage yield.

The combustion of methyl alcohol in an abundant excess of oxygen follows the equation $$ 2 \mathrm{CH}_{3} \mathrm{OH}+3 \mathrm{O}_{2} \longrightarrow 2 \mathrm{CO}_{2}+4 \mathrm{H}_{2} \mathrm{O} $$ When \(6.40 \mathrm{~g}\) of \(\mathrm{CH}_{3} \mathrm{OH}\) was mixed with \(10.2 \mathrm{~g}\) of \(\mathrm{O}_{2}\) and ignited, \(6.12 \mathrm{~g}\) of \(\mathrm{CO}_{2}\) was obtained. What was the percentage yield of \(\mathrm{CO}_{2} ?\)

Lead compounds are often highly colored and are toxic to mold, mildew, and bacteria, properties that in the past were useful for paints used before 1960 . Today we know lead is very hazardous and it is not used in paint; however, old paint is still a problem. If a certain lead-based paint contains \(14.5 \% \mathrm{PbCr}_{2} \mathrm{O}_{7}\) and \(73 \%\) of the paint evaporates as it dries, what mass of lead will be in a paint chip that weighs \(0.15 \mathrm{~g}\) ?

A compound of \(\mathrm{Ca}, \mathrm{C}, \mathrm{N},\) and \(\mathrm{S}\) was subjected to quantitative analysis and formula mass determination, and the following data were obtained. A \(0.250 \mathrm{~g}\) sample was mixed with \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) to convert all of the Ca to \(0.160 \mathrm{~g}\) of \(\mathrm{CaCO}_{3}\). A \(0.115 \mathrm{~g}\) sample of the compound was carried through a series of reactions until all of its \(S\) was changed to \(0.344 \mathrm{~g}\) of \(\mathrm{BaSO}_{4}\). A \(0.712 \mathrm{~g}\) sample was processed to liberate all of its \(\mathrm{N}\) as \(\mathrm{NH}_{3}\), and \(0.155 \mathrm{~g}\) of \(\mathrm{NH}_{3}\) was obtained. The formula mass was found to be 156 . Determine the empirical and molecular formulas of this compound.

A lawn fertilizer is rated as \(6.00 \%\) nitrogen, meaning \(6.00 \mathrm{~g}\) of \(\mathrm{N}\) in \(100 \mathrm{~g}\) of fertilizer. The nitrogen is present in the form of urea, \(\left(\mathrm{NH}_{2}\right)_{2} \mathrm{CO} .\) How many grams of urea are present in \(100 \mathrm{~g}\) of the fertilizer to supply the rated amount of nitrogen?

For a research project, a student decided to test the effect of the lead(II) ion \(\left(\mathrm{Pb}^{2+}\right)\) on the ability of salmon eggs to hatch. This ion was obtainable from the water-soluble salt, lead(II) nitrate, \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2},\) which the student decided to make by the following reaction. (The desired product was to be isolated by the slow evaporation of the water.) \(\mathrm{PbO}(s)+2 \mathrm{HNO}_{3}(a q) \longrightarrow \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(a q)+\mathrm{H}_{2} \mathrm{O}\) Losses of product for various reasons were expected, and a yield of \(86.0 \%\) was expected. In order to have \(5.00 \mathrm{~g}\) of product at this yield, how many grams of \(\mathrm{PbO}\) should be taken? (Assume that sufficient nitric acid, \(\mathrm{HNO}_{3}\), would be used.

Chlorine atoms cause chain reactions in the stratosphere that destroy ozone that protects the earth's surface from ultraviolet radiation. The chlorine atoms come from chlorofluorocarbons, compounds that contain carbon, fluorine, and chlorine, which were used for many years as refrigerants. One of these compounds is Freon-12, \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\). If a sample contains \(1.0 \times 10^{-9} \mathrm{~g}\) of \(\mathrm{Cl}\), how many grams of \(\mathrm{F}\) should be present if all of the \(\mathrm{F}\) and \(\mathrm{Cl}\) atoms in the sample came from \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) molecules?

Lime, \(\mathrm{CaO},\) can be produced in two steps as shown in the equations below. If the percentage yield of the first step is \(83.5 \%\) and the percentage yield of the second step is \(71.4 \%\), what is the expected overall percentage yield for producing \(\mathrm{CaO}\) from \(\mathrm{CaCl}_{2} ?\) $$ \begin{aligned} \mathrm{CaCl}_{2}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{CaCO}_{3}(s)+2 \mathrm{HCl}(a q) \\ \mathrm{CaCO}_{3}(s) \stackrel{\text { heat }}{\longrightarrow} \mathrm{CaO}(s)+\mathrm{CO}_{2}(g) \end{aligned} $$