Three Major Classes of Chemical Reactions

Sodium peroxide (Na₂O₂) is often used in self-contained breathing devices, such as those used in fire emergencies, because it reacts with exhaled CO₂ to form Na₂CO₃ and O₂. How many liters of respired air can react with 80.0 g of Na₂O₂ if each liter of respired air contains 0.0720 g of CO₂?

A student forgets to weigh a mixture of sodium bromide dehydrate and magnesium bromide hexahydrate. Upon strong heating, the sample loses 252.1 mg of water. The mixture of anhydrous salts reacts with excess AgNO₃ solution to form 6.00x10^-3 mol of solid AgBr. Find the mass % of each compound in the original mixture.

Magnesium is used in lightweight alloys for airplane bodies and other structures. The metal is obtained from seawater in a process that includes precipitation, neutralization, evaporation, and electrolysis. How many kilograms of magnesium can be obtained from 1.00 km³ of seawater if the initial Mg²⁺ concentration is 0.13% by mass (d of seawater = 1.04 g/mL)?

A typical formulation for window glass is 75% SiO₂, 15% Na₂O, and 10.% CaO by mass. What masses of sand (SiO₂), sodium carbonate, and calcium carbonate must be combined to produce 1.00 kg of glass after carbon dioxide is driven off by thermal decomposition of the carbonates?

Physicians who specialize in sports medicine routinely treat athletes and dancers. Ethyl chloride, a local anesthetic commonly used for simple injuries, is the product of the combination of ethylene with hydrogen chloride:

 ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{4}}\left(g\right)\mathbf{+}\mathbf{HCI}\left(g\right)\mathbf{\to }{\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{5}}\mathbf{CI}\left(g\right)$

If 0.100 kg of C2H4 and 0.100 kg of HCl react:

(a) How many molecules of gas (reactants plus products) are present when the reaction is complete?

(b) How many moles of gas are present when half the product forms?

The salinity of a solution is defined as the grams of total salts per kilogram of solution. An agricultural chemist uses a solution whose salinity is 35.0 g/kg to test the effect of irrigating farmland with high-salinity river water. The two solutes are NaCl and MgSO₄, and there are twice as many moles of NaCl as MgSO₄. What masses of NaCl and MgSO₄ are contained in 1.00 kg of the solution?

Thyroxine (C₁₅H₁₁I₄NO₄) is a hormone synthesized by the thyroid gland and used to control many metabolic functions in the body. A physiologist determines the mass percent of thyroxine in a thyroid extract by igniting 0.4332 g of extract with sodium carbonate, which converts the iodine to iodide. The iodide is dissolved in water, and bromine and hydrochloric acid are added, which convert the iodide to iodate.

(a) How many moles of iodate form per mole of thyroxine?

(b) Excess bromine is boiled off and more iodide is added, which reacts as shown in the following unbalanced equation: 

${\mathbf{IO}}_{\mathbf{3}}^{\mathbf{-}}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{H}}^{\mathbf{+}}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{I}}^{\mathbf{-}}\left(\mathrm{aq}\right)\mathbf{\to }{\mathbf{I}}_{\mathbf{2}}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\left(I\right)$ 

How many moles of iodine are produced per mole of thyroxine?

(Hint: Be sure to balance the charges as well as the atoms.) What are the oxidizing and reducing agents in the reaction?

(c) The iodine reacts completely with 17.23 mL of 0.1000 M thiosulfate as shown in the following unbalanced equation:

${\mathbf{I}}_{\mathbf{2}}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{S}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}^{\mathbf{2}\mathbf{-}}\left(\mathrm{aq}\right)\mathbf{\to }{\mathbf{I}}^{\mathbf{-}}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{S}}_{\mathbf{4}}{\mathbf{O}}_{\mathbf{6}}^{\mathbf{2}\mathbf{-}}\left(\mathrm{aq}\right)$ 

What is the mass percent of thyroxine in the thyroid extract?

Question: Over time, as their free fatty acid (FFA) content increases, edible fats and oils become rancid. To measure rancidity, the fat or oil is dissolved in ethanol, and any FFA present is titrated with KOH dissolved in ethanol. In a series of tests on olive oil, a stock solution of 0.050 M ethanolic KOH was prepared at 25⁰ C , stored at 0^oC, and then placed in a 100-mL buret to titrate any oleic acid $\left[{\mathbf{CH}}_{\mathbf{3}}{\left({\mathbf{CH}}_{\mathbf{2}}\right)}_{\mathbf{7}}\mathbf{CH}\mathbf{=}\mathbf{CH}{\left({\mathbf{CH}}_{\mathbf{2}}\right)}_{\mathbf{7}}\mathbf{COOH}\right]$ present in the oil. Each of four 10.00-g samples of oil took several minutes to titrate: the first required 19.60 mL, the second 19.80 mL, and the third and fourth 20.00 mL of the ethanolic KOH.

(a) What is the apparent acidity of each sample, in terms of mass % of oleic acid? (Note: As the ethanolic KOH warms in the buret, its volume increases by a factor of  .)

(b) Is the variation in acidity a random or systematic error? Explain.

(c) What is the actual acidity? How would you demonstrate this?

Carbon dioxide is removed from the atmosphere of space capsules by reaction with a solid metal hydroxide. The products are water and the metal carbonate.

(a) Calculate the mass of CO₂that can be removed by reaction with 3.50 kg of lithium hydroxide.

(b) How many grams of CO₂ can be removed by 1.00 g of each of the following: lithium hydroxide, magnesium hydroxide, and aluminum hydroxide?

A chemist mixes solid AgCl, CuCl₂, and MgCl₂ in enough water to give a final volume of 50.0 mL.

(a) With ions shown as spheres and solvent molecules omitted for clarity, which of the following best represents the resulting mixture?

(b) If each sphere represents 5.0x10^-3mol of ions, what is the total concentration of dissolved (separated) ions?

(c) What is the total mass of solid?

Calcium dihydrogen phosphate, Ca(H₂PO₄)₂, and sodium hydrogen carbonate, NaHCO₃, are ingredients of baking powder that react with each other to produce CO₂, which causes dough or batter to rise:

$\mathbf{Ca}{\left(H_2{\mathrm{PO}}_4\right)}_{\mathbf{2}}\left(s\right)\mathbf{+}{\mathbf{NaHCO}}_{\mathbf{3}}\left(s\right)\mathbf{\to }{\mathbf{CO}}_{\mathbf{2}}\left(g\right)\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\left(g\right)\mathbf{+}{\mathbf{CaHPO}}_{\mathbf{4}}\left(s\right)\mathbf{+}{\mathbf{Na}}_{\mathbf{2}}{\mathbf{HPO}}_{\mathbf{4}}\left(s\right)$

 [unbalanced]

If the baking powder contains 31% NaHCO₃and 35% Ca(H₂PO₄)₂ by mass:

(a) How many moles of CO₂ are produced from 1.00 g of baking powder?

(b) If 1 mol of CO₂ occupies 37.0 L at 350_F (a typical baking temperature), what volume of CO₂is produced from 1.00 g of baking powder?

In a titration of HNO₃, you add a few drops of phenolphthalein indicator to 50.00 mL of acid in a flask. You quickly add 20.00 mL of 0.0502 M NaOH but overshoot the end point, and the solution turns deep pink. Instead of starting over, you add 30.00 mL of the acid, and the solution turns colorless. Then, it takes 3.22 mL of the NaOH to reach the end point. (a) What is the concentration of the HNO₃solution? (b) How many moles of NaOH were in excess after the first addition?

The active compound in Pepto-Bismol contains C, H, O, and Bi.

(a) When 0.22105 g of it was burned in excess O2, 0.1422 g of bismuth(III) oxide, 0.1880 g of carbon dioxide, and 0.02750 g of water were formed. What is the empirical formula of this compound?

(b) Given a molar mass of 1086 g/mol, determine the molecular formula.

(c) Complete and balance the acid-base reaction between bismuth(III) hydroxide and salicylic acid (HC7H5O3), which is used to form this compound.

(d) A dose of Pepto-Bismol contains 0.600 mg of the active ingredient. If the yield of the reaction in part (c) is 88.0%, what mass (in mg) of bismuth(III) hydroxide is required to prepare one dose?

In the process of salting-in, protein solubility in a dilute salt solution is increased by adding more salt. Because the protein solubility depends on the total ion concentration as well as the ion charge, salts yielding doubly charged ions are often more effective than those yielding singly charged ions. (a) How many grams of MgCl₂ must dissolve to equal the ion concentration of 12.4 g of NaCl? (b) How many grams of CaS must dissolve? (c) Which of the three salt solutions would dissolve the most protein?

In the process of pickling, rust is removed from newly produced steel by washing the steel in hydrochloric acid:

$\left(1\right)\mathbf{6}\mathbf{HCl}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{Fe}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}\left(s\right)\mathbf{\to }\mathbf{2}{\mathbf{FeCl}}_{\mathbf{3}}\left(\mathrm{aq}\right)\mathbf{+}\mathbf{3}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\left(l\right)$ 

During the process, some iron is lost as well:

$\left(2\right)\mathbf{2}\mathbf{HCl}\left(\mathrm{aq}\right)\mathbf{+}\mathbf{Fe}\left(s\right)\mathbf{\to }{\mathbf{FeCl}}_{\mathbf{2}}\left(\mathrm{aq}\right)\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\left(g\right)$ 

(a) Which reaction, if either, is a redox process? (b) If reaction 2 did not occur and all the HCl were used, how many grams of Fe₂O₃ could be removed and FeCl₃ produced in a 2.50x10³-L bath of 3.00 M HCl? (c) If reaction 1 did not occur and all the HCl were used, how many grams of Fe could be lost and FeCl₂ produced in a 2.50x10₃-L bath of 3.00 M HCl? (d) If 0.280 g of Fe is lost per gram of Fe₂O₃ removed, what is the mass ratio of FeCl₂ to FeCl₃?

At liftoff, a space shuttle uses a solid mixture of ammonium perchlorate and aluminum powder to obtain great thrust from the volume change of solid to gas. In the presence of a catalyst, the mixture forms solid aluminum oxide and aluminium trichloride and gaseous water and nitrogen monoxide. (a) Write a balanced equation for the reaction, and identify the reducing and oxidizing agents. (b) How many total moles of gas (water vapor and nitrogen monoxide) are produced when 50.0 kg of ammonium perchlorate reacts with a stoichiometric amount of Al? (c) What is the volume change from this reaction? (d of NH₄ClO₄ = 1.95 g/cc, Al = 2.70 g/cc, Al₂O₃ = 3.97 g/cc, and AlCl₃ = 2.44 g/cc; assume 1 mol of gas occupies 22.4 L.)

A reaction cycle for an element is a series of reactions beginning and ending with that element. In the following copper reaction cycle, copper has either a 0 or a _2 oxidation state. Write balanced molecular and net ionic equations for each step in the cycle.

(1) Copper metal reacts with aqueous bromine to produce a green-blue solution.

(2) Adding aqueous sodium hydroxide forms a blue precipitate.

(3) The precipitate is heated and turns black (water is released).

(4) The black solid dissolves in nitric acid to give a blue solution.

(5) Adding aqueous sodium phosphate forms a green precipitate.

(6) The precipitate forms a blue solution in sulfuric acid.

(7) Copper metal is recovered from the blue solution when zinc metal is added.

Question: The amount of ascorbic acid (vitamin C; C₆H₈O₆) in tablets is determined by reaction with bromine and then titration of the hydrobromic acid with standard base:

 $$\begin{gathered} {\mathit{C}}_{\mathbf{6}}{\mathit{H}}_{\mathbf{8}}{\mathit{O}}_{\mathbf{6}}\mathbf{+}\mathit{B}{\mathit{r}}_{\mathbf{2}}\mathbf{\to }{\mathit{C}}_{\mathbf{6}}{\mathit{H}}_{\mathbf{6}}{\mathit{O}}_{\mathbf{6}}\mathbf{+}\mathbf{2}\mathit{H}\mathit{B}\mathit{r} \\ \mathit{H}\mathit{B}\mathit{r}\mathbf{+}\mathit{N}\mathit{a}\mathit{O}\mathit{H}\mathbf{\to }\mathit{N}\mathit{a}\mathit{B}\mathit{r}\mathbf{+}{\mathit{H}}_{\mathbf{2}}\mathit{O} \end{gathered}$$

A certain tablet is advertised as containing 500 mg of vitamin C. One tablet was dissolved in water and reacted with Br₂. The solution was then titrated with 43.20 mL of 0.1350 M NaOH. Did the tablet contain the advertised quantity of vitamin C?

Question: In 1997, at the United Nations Conference on Climate Change, the major industrial nations agreed to expand their research efforts to develop renewable sources of carbon-based fuels. For more than a decade, Brazil has been engaged in a program to replace gasoline with ethanol derived from the root crop manioc (cassava).

(a) Write separate balanced equations for the complete combustion of ethanol (C₂H₅OH) and of gasoline (represented by the formula C₈H₁₈).

(b) What mass of oxygen is required to burn completely 1.00 L of a mixture that is 90.0% gasoline (d = 0.742 g/mL) and 10.0% ethanol (d = 0.789 g/mL) by volume?

(c) If 1.00 mol of O₂ occupies 22.4 L, what volume of O₂ is needed to burn 1.00 L of the mixture?

(d) Air is 20.9% O₂ by volume. What volume of air is needed to burn 1.00 L of the mixture?

Question: In a car engine, gasoline (represented by C8H18) does not burn completely, and some CO, a toxic pollutant, forms along with CO2 and H2O. If 5.0% of the gasoline forms CO:

(a) What is the ratio of CO₂ to CO molecules in the exhaust?

(b) What is the mass ratio of CO₂ to CO?

(c) What percentage of the gasoline must form CO for the mass ratio of CO₂ to CO to be exactly 1/1?