Chapter 4

A noncarbonated soft drink contains an unknown amount of citric acid, \(\mathrm{H}_{3} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}_{7}\). If \(100 .\) mL of the soft drink requires \(33.51 \mathrm{mL}\) of \(0.0102 \mathrm{M} \mathrm{NaOH}\) to neutralize the citric acid completely, what mass of citric acid does the soft drink contain per 100. mL? The reaction of citric acid and NaOH is $$\mathrm{H}_{3} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}_{7}(\mathrm{aq})+3 \mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{Na}_{3} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}_{7}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\ell)$$

Sodium thiosulfate, \(\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3},\) is used as a "fixer" in black-and-white photography. Suppose you have a bottle of sodium thiosulfate and want to determine its purity. The thiosulfate ion can be oxidized with \(\mathrm{I}_{2}\) according to the balanced, net ionic equation $$\mathrm{I}_{2}(\mathrm{aq})+2 \mathrm{S}_{2} \mathrm{O}_{3}^{2-}(\mathrm{aq}) \rightarrow 2 \mathrm{I}^{-}(\mathrm{aq})+\mathrm{S}_{4} \mathrm{O}_{6}^{2-}(\mathrm{aq})$$ If you use \(40.21 \mathrm{mL}\) of \(0.246 \mathrm{M} \mathrm{I}_{2}\) in a titration, what is the weight percent of \(\mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}\) in a \(3.232-\mathrm{g}\) sample of impure material?

You have a mixture of oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4},\) and another solid that does not react with sodium hydroxide. If 29.58 mL of \(0.550 \mathrm{M} \mathrm{NaOH}\) is required to titrate the oxalic acid in the \(4.554-\mathrm{g}\) sample to the second equivalence point, what is the mass percent of oxalic acid in the mixture? Oxalic acid and NaOH react according to the equation $$\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+2 \mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$

(a) What is the pH of a 0.105 M HCl solution? (b) What is the hydronium ion concentration in a solution with a pH of \(2.56 ?\) Is the solution acidic or basic? (c) A solution has a pH of 9.67. What is the hydronium ion concentration in the solution? Is the solution acidic or basic? (d) A 10.0 -mL sample of \(2.56 \mathrm{M}\) HCl is diluted with water to \(250 .\) mL. What is the pH of the dilute solution?

A solution of hydrochloric acid has a volume of \(125 \mathrm{mL}\) and a pH of \(2.56 .\) What mass of \(\mathrm{NaHCO}_{3}\) must be added to completely consume the HCl?

One half liter (500. mL) of 2.50 M HCl is mixed with \(250 .\) mL of \(3.75 \mathrm{M}\) HCl. Assuming the total solution volume after mixing is \(750 . \mathrm{mL}\) what is the concentration of hydrochloric acid in the resulting solution? What is its pH?

A solution of hydrochloric acid has a volume of \(250 .\) mL and a pH of \(1.92 .\) Exactly \(250 .\) mL of \(0.0105 \mathrm{M} \mathrm{NaOH}\) is added. What is the \(\mathrm{pH}\) of the resulting solution?

You place \(2.56 \mathrm{g}\) of \(\mathrm{CaCO}_{3}\) in a beaker containing \(250 .\) mL of \(0.125 \mathrm{M}\) HCl. When the reaction has ceased, does any calcium carbonate remain? What mass of \(\mathrm{CaCl}_{2}\) can be produced? $$\mathrm{CaCO}_{3}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+\mathrm{CO}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\ell)$$

The cancer drug cisplatin, \(\operatorname{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2},\) can be made by reacting \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{PtCl}_{4}\) with ammonia in aqueous solution. Besides cisplatin, the other product is \(\mathrm{NH}_{4} \mathrm{Cl}\). (a) Write a balanced equation for this reaction. (b) To obtain \(12.50 \mathrm{g}\) of cisplatin, what mass of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{PtCl}_{4}\) is required? What volume of \(0.125 \mathrm{M} \mathrm{NH}_{3}\) is required? (c) Cisplatin can react with the organic compound pyridine, \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N},\) to form a new compound. $$\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}(\mathrm{aq})+x \mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}(\mathrm{aq}) \rightarrow \mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}\right)_{x}(\mathrm{s})$$ Suppose you treat 0.150 g of cisplatin with what you believe is an excess of liquid pyridine \((1.50 \mathrm{mL} ; d=0.979 \mathrm{g} / \mathrm{mL}) .\) When the reaction is complete, you can find out how much pyridine was not used by titrating the solution with standardized HCl. If 37.0 mL of 0.475 M HCl is required to titrate the excess pyridine, $$\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}(\mathrm{aq})+\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{C}_{5} \mathrm{H}_{5} \mathrm{NH}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})$$ what is the formula of the unknown compound \(\operatorname{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\left(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}\right)_{x} ?\)

You need to know the volume of water in a small swimming pool, but, owing to the pool's irregular shape, it is not a simple matter to determine its dimensions and calculate the volume. To solve the problem, you stir in a solution of a dye (1.0 g of methylene blue, \(\mathrm{C}_{16} \mathrm{H}_{18} \mathrm{ClN}_{3} \mathrm{S}\), in \(50.0 \mathrm{mL}\) of water). After the dye has mixed with the water in the pool, you take a sample of the water. Using a spectrophotometer, you determine that the concentration of the dye in the pool is \(4.1 \times 10^{-8} \mathrm{M}\) What is the volume of water in the pool?

Calcium and magnesium carbonates occur together in the mineral dolomite. Suppose you heat a sample of the mineral to obtain the oxides, \(\mathrm{CaO}\) and \(\mathrm{MgO},\) and then treat the oxide sample with hydrochloric acid. If \(7.695 \mathrm{g}\) of the oxide sample requires \(125 \mathrm{mL}\) of \(2.55 \mathrm{M} \mathrm{HCl},\) $$\begin{aligned} \mathrm{CaO}(\mathrm{s}) &+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell) \\\\\mathrm{MgO}(\mathrm{s}) &+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{MgCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)\end{aligned}$$ what is the weight percent of each oxide (CaO and \(\mathrm{MgO}\) ) in the sample?

You mix \(25.0 \mathrm{mL}\) of \(0.234 \mathrm{M} \mathrm{FeCl}_{3}\) with \(42.5 \mathrm{mL}\) of \(0.453 \mathrm{M} \mathrm{NaOH}\). (a) What mass of \(\mathrm{Fe}(\mathrm{OH})_{3}\) (in grams) will precipitate from this reaction mixture? (b) One of the reactants \(\left(\mathrm{FeCl}_{3} \text { or } \mathrm{NaOH}\right)\) is present in a stoichiometric excess. What is the molar concentration of the excess reactant remaining in solution after \(\operatorname{Fe}(\mathrm{OH})_{3}\) has been precipitated?

ATOM ECONOMY: Ethylene oxide, \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O},\) is an important industrial chemical [as it is the starting place to make such important chemicals as ethylene glycol (antifreeze) and various polymers One way to make the compound is called the "chlorohydrin route." $$\mathrm{C}_{2} \mathrm{H}_{4}+\mathrm{Cl}_{2}+\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}+\mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O}$$ Another route is the modern catalytic reaction. $$\mathrm{C}_{2} \mathrm{H}_{4}+1 / 2 \mathrm{O}_{2} \rightarrow \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}$$ (a) Calculate the \% atom economy for the production of \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}\) in each of these reactions. Which is the more efficient method? (b) What is the percent yield of \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}\) if 867 g of \(\mathrm{C}_{2} \mathrm{H}_{4}\) is used to synthesize \(762 \mathrm{g}\) of the product by the catalytic reaction?

Suppose you dilute \(25.0 \mathrm{mL}\) of a \(0.110 \mathrm{M}\) solution of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) to exactly \(100.0 \mathrm{mL}\). You then take exactly \(10.0 \mathrm{mL}\) of this diluted solution and add it to a 250-mL volumetric flask. After filling the volumetric flask to the mark with distilled water (indicating the volume of the new solution is \(250 . \mathrm{mL}\) ), what is the concentration of the diluted \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) solution?

In some laboratory analyses, the preferred technique is to dissolve a sample in an excess of acid or base and then "back-titrate" the unreacted acid or base with a standard base or acid. To assess the purity of a sample of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) you dissolve a 0.475 -g sample of impure \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) in aqueous KOH. $$\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(\mathrm{aq})+2 \mathrm{KOH}(\mathrm{aq}) \rightarrow 2 \mathrm{NH}_{3}(\mathrm{aq})+\mathrm{K}_{2} \mathrm{SO}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$ The \(\mathrm{NH}_{3}\) liberated in the reaction is distilled from the solution into a flask containing \(50.0 \mathrm{mL}\) of 0.100 M HCl. The ammonia reacts with the acid to produce \(\mathrm{NH}_{4} \mathrm{Cl},\) but not all of the HCl is used in this reaction. The amount of excess acid is determined by titrating the solution with standardized NaOH. This titration consumes \(11.1 \mathrm{mL}\) of 0.121 M NaOH. What is the weight percent of \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\) in the 0.475 -g sample?

Oyster beds in the oceans require chloride ions for growth. The minimum concentration is \(8 \mathrm{mg} / \mathrm{L}\) (8 parts per million). To analyze for the amount of chloride ion in a 50.0 -mL sample of water, you add a few drops of aqueous potassium chromate and then titrate the sample with \(25.60 \mathrm{mL}\) of 0.001036 M silver nitrate. The silver nitrate reacts with chloride ion, and, when the ion is completely removed, the silver nitrate reacts with potassium chromate to give a red precipitate. (a) Write a balanced net ionic equation for the reaction of silver nitrate with chloride ions. (b) Write a complete balanced equation and a net ionic equation for the reaction of silver nitrate with potassium chromate, indicating whether each compound is water-soluble or not. (c) What is the concentration of chloride ions in the sample? Is it sufficient to promote oyster growth?

A compound consisting of yttrium(III) ions, barium(II) ions, both copper(II) and copper(III) ions, and oxide ions is a superconducting material at low temperatures (pages \(158-159) .\) It has the formula \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7-x}\) where \(x\) is a variable between 1 and \(0 .\) To find out the value of \(x,\) you dissolve \(34.02 \mathrm{mg}\) of the compound in \(5 \mathrm{mL}\) of 1.0 M HCl. Bubbles of oxygen gas \(\left(\mathrm{O}_{2}\right)\) are observed as the following reaction occurs: $$\begin{array}{l}\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7-\mathrm{x}}(\mathrm{s})+13 \mathrm{H}^{+}(\mathrm{aq}) \rightarrow \\\\\qquad \begin{aligned}\mathrm{Y}^{3+}(\mathrm{aq}) &+2 \mathrm{Ba}^{+}(\mathrm{aq})+3 \mathrm{Cu}^{2+}(\mathrm{aq}) \\\\+1 / 4(1-2 x) & \mathrm{O}_{2}(\mathrm{g})+13 / 2 \mathrm{H}_{2} \mathrm{O}(\ell) \end{aligned} \end{array}$$ You then boil the solution, cool it, and add \(10 \mathrm{mL}\) of 0.70 M KI under argon. The following reaction occurs: $$2 \mathrm{Cu}^{2+}(\mathrm{aq})+5 \mathrm{I}^{-}(\mathrm{aq}) \rightarrow 2 \mathrm{CuI}(\mathrm{s})+\mathrm{I}_{3}^{-}(\mathrm{aq})$$ When this reaction is complete, a titration of the resulting solution with sodium thiosulfate requires \(1.542 \times 10^{-4} \mathrm{mol} \mathrm{S}_{2} \mathrm{O}_{3}^{2-}(\mathrm{aq})\) $$\mathrm{I}_{3}^{-}(\mathrm{aq})+2 \mathrm{S}_{2} \mathrm{O}_{3}^{2-}(\mathrm{aq}) \rightarrow 3 \mathrm{I}^{-}(\mathrm{aq})+\mathrm{S}_{4} \mathrm{O}_{6}^{2-}(\mathrm{aq})$$ What is the value of \(x\) in \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7-x} ?\)

You wish to determine the weight percent of copper in a copper-containing alloy. After dissolving a \(0.251-g\) sample of the alloy in acid, an excess of KI is added, and the \(\mathrm{Cu}^{2+}\) and \(\mathrm{I}^{-}\) ions undergo the reaction $$2 \mathrm{Cu}^{2+}(\mathrm{aq})+5 \mathrm{I}^{-}(\mathrm{aq}) \rightarrow 2 \mathrm{CuI}(\mathrm{s})+\mathrm{I}_{3}^{-}(\mathrm{aq})$$ The liberated \(\mathrm{I}_{3}^{-}\) is titrated with sodium thiosulfate according to the equation $$\mathrm{I}_{3}^{-}(\mathrm{aq})+2 \mathrm{S}_{2} \mathrm{O}_{3}^{2-}(\mathrm{aq}) \rightarrow \mathrm{S}_{4} \mathrm{O}_{6}^{2-}(\mathrm{aq})+3 \mathrm{I}^{-}(\mathrm{aq})$$ (a) Designate the oxidizing and reducing agents in the two reactions above. (b) If \(26.32 \mathrm{mL}\) of \(0.101 \mathrm{M} \mathrm{Na}_{2} \mathrm{S}_{2} \mathrm{O}_{3}\) is required for titration to the equivalence point, what is the weight percent of Cu in the alloy?

A compound has been isolated that can have either of two possible formulas: (a) \(\mathrm{K}\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]\) or \((\mathrm{b}) \mathrm{K}_{3}\left[\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right] .\) To find which is correct, you dissolve a weighed sample of the compound in acid, forming oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} .\) You then titrate this acid with potassium permanganate, \(\mathrm{KMnO}_{4}\) (the source of the \(\mathrm{MnO}_{4}^{-}\) ion). The balanced, net ionic equation for the titration is $$5 \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(\mathrm{aq})+2 \mathrm{MnO}_{4}^{-}(\mathrm{aq})+6 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \rightarrow 2 \mathrm{Mn}^{2+}(\mathrm{aq})+10 \mathrm{CO}_{2}(\mathrm{g})+14 \mathrm{H}_{2} \mathrm{O}(\ell)$$ Titration of 1.356 g of the compound requires \(34.50 \mathrm{mL}\) of \(0.108 \mathrm{M} \mathrm{KMnO}_{4} .\) Which is the correct formula of the iron-containing compound: (a) or (b)?

Chromium(III) chloride forms many compounds with ammonia. To find the formula of one of these compounds, you titrate the \(\mathrm{NH}_{3}\) in the compound with standardized acid. $$\begin{array}{rl}\operatorname{Cr}\left(\mathrm{NH}_{3}\right)_{x} \mathrm{Cl}_{3}(\mathrm{aq})+ & x \mathrm{HCl}(\mathrm{aq}) \rightarrow \\\x & \mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{Cr}^{3+}(\mathrm{aq})+(x+3) \mathrm{Cl}^{-}(\mathrm{aq})\end{array}$$ Assume that \(24.26 \mathrm{mL}\) of \(1.500 \mathrm{M} \mathrm{HCl}\) is used to titrate \(1.580 \mathrm{g}\) of \(\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{x} \mathrm{Cl}_{3} .\) What is the value of \(x ?\)

Thioridazine, \(\mathrm{C}_{21} \mathrm{H}_{26} \mathrm{N}_{2} \mathrm{S}_{2},\) is a pharmaceutical agent used to regulate dopamine. (Dopamine, a neurotransmitter, affects brain processes that control movement, emotional response, and ability to experience pleasure and pain.) A chemist can analyze a sample of the pharmaceutical for the thioridazine content by decomposing it to convert the sulfur in the compound to sulfate ion. This is then "trapped" as water-insoluble barium sulfate (see Figure 4.4). $$\begin{aligned}&\mathrm{SO}_{4}^{2-}(\mathrm{aq}, \text { from thioridazine })+\mathrm{BaCl}_{2}(\mathrm{aq}) \rightarrow\\\&\mathrm{BaSO}_{4}(\mathrm{s})+2 \mathrm{Cl}^{-}(\mathrm{aq}) \end{aligned}$$ Suppose a 12 -tablet sample of the drug yielded \(0.301 \mathrm{g}\) of \(\mathrm{BaSO}_{4} .\) What is the thioridazine content, in milligrams, of each tablet?

A herbicide contains \(2,4-\mathrm{D}\) \((2,4-\text { dichlorophenoxyacetic acid }), \mathrm{C}_{8} \mathrm{H}_{6} \mathrm{Cl}_{2} \mathrm{O}_{3} . \mathrm{A}\) \(1.236-\mathrm{g}\) sample of the herbicide was decomposed to liberate the chlorine as \(\mathrm{Cl}^{-}\) ion. This was precipitated as AgCl, with a mass of 0.1840 g. What is the mass percent of \(2,4-\mathrm{D}\) in the sample?

Anhydrous calcium chloride is a good drying agent because it will rapidly pick up water. Suppose you have stored some carefully dried \(\mathrm{CaCl}_{2}\) in a desiccator. Unfortunately, someone did not close the top of the desiccator tightly, and the \(\mathrm{CaCl}_{2}\) became partially hydrated. A \(150-\mathrm{g}\) sample of this partially hydrated material was dissolved in \(80 \mathrm{g}\) of hot water. When the solution was cooled to \(20^{\circ} \mathrm{C}, 74.9 \mathrm{g}\) of \(\mathrm{CaCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) precipitated. Knowing the solubility of calcium chloride in water at \(20^{\circ} \mathrm{C}\) is \(74.5 \mathrm{g} \mathrm{CaCl}_{2} / 100 \mathrm{g}\) water, determine the water content of the 150 -g sample of partially hydrated calcium chloride (in moles of water per mole of \(\mathrm{CaCl}_{2}\) ).

Phosphate in urine can be determined by spectrophotometry. After removing protein from the sample, it is treated with a molybdenum compound to give, ultimately, a deep blue polymolybdate. The absorbance of the blue polymolybdate can be measured at \(650 \mathrm{nm}\) and is directly related to the urine phosphate concentration. A 24 -hour urine sample was collected from a patient; the volume of urine was 1122 mL. The phosphate in a 1.00 mL portion of the urine sample was converted to the blue polymolybdate and diluted to 50.00 mL. A calibration curve was prepared using phosphate-containing solutions. (Concentrations are reported in grams of phosphorus (P) per liter of solution.) $$\begin{array}{|c|c|}\hline \text { Solution (mass P/L) } & \begin{array}{c}\text { Absorbance at } 650 \mathrm{nm} \\\\\text { in a } 1.0-\mathrm{cm} \text { cell }\end{array} \\\\\hline 1.00 \times 10^{-6} \mathrm{g} & 0.230 \\\\\hline 2.00 \times 10^{-6} \mathrm{g} & 0.436 \\\\\hline 3.00 \times 10^{-6} \mathrm{g} & 0.638 \\\\\hline 4.00 \times 10^{-6} \mathrm{g} & 0.848 \\ \hline \text { Urine sample } & 0.518 \\\\\hline\end{array}$$ (a) What are the slope and intercept of the calibration curve? (b) What is the mass of phosphorus per liter of urine? (c) What mass of phosphate did the patient excrete in the one-day period?

A \(4.000-\mathrm{g}\) sample containing \(\mathrm{KCl}\) and \(\mathrm{KClO}_{4}\) was dissolved in sufficient water to give \(250.00 \mathrm{mL}\) of solution. A 50.00 -mL portion of the solution required \(41.00 \mathrm{mL}\) of \(0.0750 \mathrm{M} \mathrm{AgNO}_{3}\) in a Mohr titration (page 209 ). Next, a 25.00 -mL portion of the original solution was treated with \(\mathrm{V}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) to reduce the perchlorate ion to chloride, $$\begin{aligned} 8 \mathrm{V}^{3+}(\mathrm{aq})+\mathrm{ClO}_{4}^{-}(\mathrm{aq})+12 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow & \\ \mathrm{Cl}^{-}(\mathrm{aq})+8 \mathrm{VO}^{2+}(\mathrm{aq}) &+8 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \end{aligned}$$ and the resulting solution was titrated with \(\mathrm{AgNO}_{3} .\) This titration required \(38.12 \mathrm{mL}\) of \(0.0750 \mathrm{M} \mathrm{AgNO}_{3} .\) What is the mass percent of KCl and \(\mathrm{KClO}_{4}\) in the mixture?

Two beakers sit on a balance; the total mass is \(167.170 \mathrm{g} .\) One beaker contains a solution of \(\mathrm{KI}\) the other contains a solution of \(\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2} .\) When the solution in one beaker is poured completely into the other, the following reaction occurs: $$2 \mathrm{KI}(\mathrm{aq})+\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{KNO}_{3}(\mathrm{aq})+\mathrm{PbI}_{2}(\mathrm{s})$$ What is the total mass of the beakers and solutions after reaction? Explain completely.

Let us explore a reaction with a limiting reactant. Here, zinc metal is added to a flask containing aqueous HCl, and \(\mathrm{H}_{2}\) gas is a product. $$\mathrm{Zn}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{ZnCl}_{2}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{g})$$ The three flasks each contain 0.100 mol of HCl. Zinc is added to each flask in the following quantities. When the reactants are combined, the \(\mathrm{H}_{2}\) inflates the balloon attached to the flask. The results are as follows: Flask 1: Balloon inflates completely, but some \(\mathrm{Zn}\) remains when inflation ceases. Flask 2: Balloon inflates completely. No Zn remains. Flask 3: Balloon does not inflate completely. No Zn remains. Explain these results. Perform calculations that support your explanation.

Antacids are chemical compounds that can give immediate relief from indigestion or heartburn because they contain carbonate or hydroxide ions that neutralize stomach acids. Some common active ingredients include \(\mathrm{NaHCO}_{3}, \mathrm{KHCO}_{3}\), \(\mathrm{CaCO}_{3}, \mathrm{Mg}(\mathrm{OH})_{2},\) and \(\mathrm{Al}(\mathrm{OH})_{3} .\) Although these compounds give quick relief, they are not recommended for prolonged consumption. Calcium carbonate may contribute to the growth of kidney stones, and calcium carbonate and aluminum hydroxide may cause constipation. Magnesium hydroxide, on the other hand, is a mild laxative that can cause diarrhea. Antacids containing magnesium, therefore, are often combined with aluminum hydroxide since the aluminum counteracts the laxative properties of the magnesium. (a) Which of the compounds listed above produce gas-forming reactions when combined with HCl? (b) One tablet of Tums Regular Strength Antacid contains \(500 . \mathrm{mg} \mathrm{CaCO}_{3}\) . (i) Write a balanced chemical equation for the reaction of \(\mathrm{CaCO}_{3}\) and stomach acid \((\mathrm{HCl})\) (ii) What volume (in mL) of 0.500 \(\mathrm{M}\) HCl(aq) will react completely with one tablet of Tums? (c) The active ingredients in Rolaids are \(\mathrm{CaCO}_{3}\) and \(\mathrm{Mg}(\mathrm{OH})_{2}\). (i) Write a balanced chemical equation for the reaction of \(\mathrm{Mg}(\mathrm{OH})_{2}\) and \(\mathrm{HCl}\). (ii) If \(29.52 \mathrm{mL}\) of \(0.500 \mathrm{M} \mathrm{HCl}\) is required to titrate one tablet of Rolaids and the tablet contains \(550 \mathrm{mg}\) of \(\mathrm{CaCO}_{3},\) what mass of \(\mathrm{Mg}(\mathrm{OH})_{2}\) is present in one tablet? (d) Maalox may be purchased in either a liquid or solid form. One teaspoon of the liquid form of Maalox" contains a mixture of \(200 . \mathrm{mg}\) of \(\mathrm{Al}(\mathrm{OH})_{3}\) and \(200 . \mathrm{mg}\) of \(\mathrm{Mg}(\mathrm{OH})_{2} .\) What volume of 0.500 \(\mathrm{M} \mathrm{HCl}(\mathrm{aq})\) will react completely with one teaspoon of Maalox \(^{\pi / 2} ?\) (e) Which product neutralizes the greatest amount of acid when taken in the quantities presented above: one tablet of Tums" or Rolaids" or one teaspoon of Maalox"?

Two students titrate different samples of the same solution of HCl using 0.100 M NaOH solution and phenolphthalein indicator (Figure 4.12 ). The first student pipets \(20.0 \mathrm{mL}\) of the HCl solution into a flask, adds \(20 \mathrm{mL}\) of distilled water and a few drops of phenolphthalein solution, and titrates until a lasting pink color appears. The second student pipets \(20.0 \mathrm{mL}\) of the HCI solution into a flask, adds \(60 \mathrm{mL}\) of distilled water and a few drops of phenolphthalein solution, and titrates to the first lasting pink color. Each student correctly calculates the molarity of an HCl solution. What will the second student's result be? (a) four times less than the first student's result (b) four times greater than the first student's result (c) two times less than the first student's result (d) two times greater than the first student's result (e) the same as the first student's result