Chapter 4

(a) How many grams of ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) , should you dissolve in water to make 1.00 \(\mathrm{L}\) of vodka (which is an aqueous solution that is 6.86 \(\mathrm{M}\) ethanol)? (b) Using the density of ethanol \((0.789 \mathrm{g} / \mathrm{mL}),\) calculate the volume of ethanol you need to make 1.00 \(\mathrm{L}\) of vodka.

One cup of fresh orange juice contains 124 \(\mathrm{mg}\) of ascorbic acid (vitamin \(\mathrm{C}, \mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6} ) .\) Given that one cup \(=236.6 \mathrm{mL}\) calculate the molarity of vitamin \(\mathrm{C}\) in orange juice.

(a) Which will have the highest concentration of potassium ion: \(0.20 M \mathrm{KCl}, 0.15 M \mathrm{K}_{2} \mathrm{CrO}_{4},\) or 0.080\(M \mathrm{K}_{3} \mathrm{PO}_{4} ?\) (b) Which will contain the greater number of moles of potassium ion: 30.0 \(\mathrm{mL}\) of 0.15 \(\mathrm{M} \mathrm{K}_{2} \mathrm{CrO}_{4}\) or 25.0 \(\mathrm{mL}\) of 0.080 \(\mathrm{M} \mathrm{K}_{3} \mathrm{PO}_{4} ?\)

In each of the following pairs, indicate which has the higher concentration of \(\mathrm{I}^{-}\) ion: (a) 0.10 \(\mathrm{M}\) BaI \(_{2}\) or 0.25 \(\mathrm{M}\) KI solution, (b) 100 \(\mathrm{mL}\) of 0.10 \(\mathrm{M}\) KI solution or 200 \(\mathrm{mL}\) of 0.040 \(\mathrm{MZnI}_{2}\) solution, \((\mathbf{c}) 3.2 \mathrm{M}\) HI solution or a solution made by dissolving 145 g of Nal in water to make 150 \(\mathrm{mL}\) of solution.

Indicate the concentration of each ion or molecule present in the following solutions: (a) 0.25\(M\) NaNO \(_{3}\) , (b) \(1.3 \times 10^{-2} M \mathrm{MgSO}_{4},(\mathbf{c}) 0.0150 M \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6},(\mathbf{d})\) a mixture of 45.0 \(\mathrm{mL}\) of 0.272 \(\mathrm{M} \mathrm{NaCl}\) and 65.0 \(\mathrm{mL}\) of 0.0247 \(\mathrm{M}\) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3} .\) Assume that the volumes are additive.

Indicate the concentration of each ion present in the solution formed by mixing (a) 42.0 \(\mathrm{mL}\) of 0.170 \(\mathrm{M} \mathrm{NaOH}\) with 37.6 \(\mathrm{mL}\) of \(0.400 \mathrm{M} \mathrm{NaOH},(\mathbf{b}) 44.0 \mathrm{mL}\) of 0.100 \(\mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}\) with 25.0 \(\mathrm{mL}\) of \(0.150 \mathrm{M} \mathrm{KCl},\) (c) 3.60 \(\mathrm{g} \mathrm{KCl}\) in 75.0 \(\mathrm{mL}\) of 0.250\(M \mathrm{CaCl}_{2}\) solution. Assume that the volumes are additive.

(a) You have a stock solution of 14.8 \(\mathrm{M} \mathrm{NH}_{3}\) . How many milliliters of this solution should you dilute to make 1000.0 \(\mathrm{mL}\) of 0.250 \(\mathrm{MNH}_{3} ?(\mathbf{b})\) you take a 10.0 -mL portion of the stock solution and dilute it to a total volume of \(0.500 \mathrm{L},\) what will be the concentration of the final solution?

(a) How many milliliters of a stock solution of 6.0 \(\mathrm{MHNO}_{3}\) would you have to use to prepare 110 \(\mathrm{mL}\) of 0.500 \(\mathrm{M} \mathrm{HNO}_{3} ?\) (b) If you dilute 10.0 \(\mathrm{mL}\) of the stock solution to a final volume of \(0.250 \mathrm{L},\) what will be the concentration of the diluted solution?

A medical lab is testing a new anticancer drug on cancer cells. The drug stock solution concentration is \(1.5 \times 10^{-9} M,\) and 1.00 \(\mathrm{mL}\) of this solution will be delivered to a dish containing \(2.0 \times 10^{5}\) cancer cells in 5.00 \(\mathrm{mL}\) of aqueous fluid. What is the ratio of drug molecules to the number of cancer cells in the dish?

Calicheamicin gamma-1, \(\mathrm{C}_{55} \mathrm{H}_{74} \mathrm{IN}_{3} \mathrm{O}_{21} \mathrm{S}_{4},\) is one of the most potent antibiotics known: one molecule kills one bacterial cell. Describe how you would (carefully!) prepare 25.00 \(\mathrm{mL} .\) of an aqueous calicheamicin gamma-1 solution that could kill \(1.0 \times 10^{8}\) bacteria, starting from a \(5.00 \times 10^{-9} M\) stock solution of the antibiotic.

Glycerol, \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3},\) is a substance used extensively in the manufacture of cosmetic s, foodstuffs, antifreeze, and plastics. Glycerol is a water-soluble liquid with a density of 1.2656 \(\mathrm{g} / \mathrm{mL}\) at \(15^{\circ} \mathrm{C}\) . Calculate the molarity of a solution of glycerol made by dissolving 50.000 \(\mathrm{mL}\) glycerol at \(15^{\circ} \mathrm{C}\) in enough water to make 250.00 \(\mathrm{mL}\) of solution.

Glycerol, \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{3},\) is a substance used extensively in the manufacture of cosmetic s, foodstuffs, antifreeze, and plastics. Glycerol is a water-soluble liquid with a density of 1.2656 \(\mathrm{g} / \mathrm{mL}\) at \(15^{\circ} \mathrm{C}\) . Calculate the molarity of a solution of glycerol made by dissolving 50.000 \(\mathrm{mL}\) glycerol at \(15^{\circ} \mathrm{C}\) in enough water to make 250.00 \(\mathrm{mL}\) of solution.

You want to analyze a silver nitrate solution. (a) You could add \(\mathrm{HCl}(a q)\) to the solution to precipitate out AgCl(s). What volume of a 0.150 \(\mathrm{M} \mathrm{HCl}(a q)\) solution is needed to precipitate the silver ions from 15.0 \(\mathrm{mL}\) of a 0.200 \(\mathrm{MgNO}_{3}\) solution? (b) You could add solid \(\mathrm{KCl}\) to the solution to precipitate out AgCl(s). What mass of KCl is needed to precipitate the silver ions from 15.0 \(\mathrm{mL}\) of 0.200 \(\mathrm{M} \mathrm{AgNO}_{3}\) solution? (c) Given that a 0.150 \(\mathrm{M} \mathrm{HCl}(a q)\) solution costs \(\$ 39.95\) for 500 \(\mathrm{mL}\) and that \(\mathrm{KCl}\) costs \(\$ 10 / \mathrm{ton},\) which analysis procedure is more cost-effective?

(a) What volume of 0.115 \(\mathrm{M} \mathrm{HClO}_{4}\) solution is needed to neutralize 50.00 \(\mathrm{mL}\) of 0.0875 \(\mathrm{M} \mathrm{NaOH} ?(\mathbf{b})\) What volume of 25.8 \(\mathrm{mL}\) of an AgNO \(_{3}\) solution is needed to precipitate all the \(\mathrm{Cl}^{-}\) ions in a 785 -mg sample of \(\mathrm{KCl}\) (forming AgCl), what is the molarity of the AgNO \(_{3}\) solution? (d) If 45.3 \(\mathrm{mL}\) of a 0.108 \(M \mathrm{HCl}\) solution is needed to neutralize a solution of \(\mathrm{KOH}\) , how many grams of \(\mathrm{KOH}\) must be present in the solution?

(a) How many milliliters of 0.120 \(\mathrm{M}\) HCl are needed to completely neutralize 50.0 \(\mathrm{mL}\) of 0.101 \(\mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\) solution? (b) How many milliliters of 0.125 \(\mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) are needed to neutralize 0.200 \(\mathrm{g}\) of NaOH? \((\mathrm{c})\) If 55.8 \(\mathrm{mL}\) of a BaCl \(_{2}\) solution is needed to precipitate all the sulfate ion in a 752 -mg sample of \(\mathrm{Na}_{2} \mathrm{SO}_{4},\) what is the molarity of the BaCl\(_{2}\) solution?

Some sulfuric acid is spilled on a lab bench. You can neutralize the acid by sprinkling sodium bicarbonate on it and then mopping up the resulting solution. The sodium bicarbonate reacts with sulfuric acid according to: \begin{equation} \begin{array}{r}{2 \mathrm{NaHCO}_{3}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \longrightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}(a q)+} \quad\\\ {2 \mathrm{H}_{2} \mathrm{O}(l)+2 \mathrm{CO}_{2}(g)}\end{array} \end{equation} Sodium bicarbonate is added until the fizzing due to the formation of \(\mathrm{CO}_{2}(g)\) stops. If 27 \(\mathrm{mL}\) of 6.0 \(\mathrm{MH}_{2} \mathrm{SO}_{4}\) was spilled, what is the minimum mass of \(\mathrm{NaHCO}_{3}\) that must be added to the spill to neutralize the acid?

The distinctive odor of vinegar is due to aceticacid, \(\mathrm{CH}_{3} \mathrm{COOH},\) which reacts with sodium hydroxide according to: $$\mathrm{CH}_{3} \mathrm{COOH}(a q)+\mathrm{NaOH}(a q) \longrightarrow_{\mathrm{H}_{2} \mathrm{O}(l)+\mathrm{NaCH}_{3} \mathrm{COO}(a q)}$$ If 3.45 \(\mathrm{mL}\) of vinegar needs 42.5 \(\mathrm{mL}\) of 0.115 \(\mathrm{M} \mathrm{NaOH}\) to reach the equivalence point in a titration, how many grams of acetic acid are in a 1.00 -qt sample of this vinegar?

A 4.36 -g sample of an unknown alkali metal hydroxide is dissolved in 100.0 \(\mathrm{mL}\) of water. An acid-base indicator is added, and the resulting solution is titrated with 2.50 \(\mathrm{M} \mathrm{HCl}(a q)\) solution. The indicator changes color, signaling that theequivalence point has been reached, after 17.0 \(\mathrm{mL}\) of the hydrochloric acid solution has been added. (a) What is the molar mass of the metal hydroxide? (b) What is the identity of the alkalimetal cation: \(\mathrm{Li}^{+}, \mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{Rb}^{+},\) or \(\mathrm{Cs}^{+} ?\)

An 8.65 -g sample of an unknown group 2 A metal hydroxide is dissolved in 85.0 \(\mathrm{mL}\) of water. An acid-base indicator is added and the resulting solution is titrated with 2.50 \(\mathrm{M}\) \(\mathrm{HCl}(a q)\) solution. The indicator changes color, signaling that the equivalence point has been reached, after 56.9 \(\mathrm{mL}\) of the hydrochloric acid solution has been added. (a) What is the molar mass of the metal hydroxide? (b) What is the identity of the metal cation: \(\mathrm{Ca}^{2+}, \mathrm{Sr}^{2+},\) or \(\mathrm{Ba}^{2+?}\) ?

A solution of 100.0 \(\mathrm{mL}\) of 0.200 \(\mathrm{M} \mathrm{KOH}\) is mixed with a solution of 200.0 \(\mathrm{mL}\) of 0.150 \(\mathrm{M} \mathrm{MiSO}_{4}\) . (a) Write the balanced chemical equation for the reaction that occurs. (b) What precipitate forms? (c) What is the limiting reactant? (d) How many grams of this precipitate form? (e) What is the concentration of each ion that remains in solution?

A solution is made by mixing 15.0 \(\mathrm{g}\) of \(\mathrm{Sr}(\mathrm{OH})_{2}\) and 55.0 \(\mathrm{mL}\) of 0.200 \(\mathrm{M} \mathrm{HNO}_{3}\) . (a) Write a balanced equation for the reaction that occurs between the solutes. (b) Calculate the concentration of each ion remaining in solution. (c) Is the resulting solution acidic or basic?

A \(0.5895-\) g sample of impure magnesium hydroxide is dissolved in 100.0 \(\mathrm{mL}\) of 0.2050 \(\mathrm{M} \mathrm{HCl}\) solution. The excess acid then needs 19.85 \(\mathrm{mL}\) of 0.1020 \(\mathrm{M} \mathrm{NaOH}\) for neutralization. Calculate the percentage by mass of magnesium hydroxide in the sample, assuming that it is the only substance reacting with the HCl solution.

A 1.248 -g sample of limestone rock is pulverized and then treated with 30.00 mL of 1.035\(M\) HCl solution. The excess acid then requires 11.56 \(\mathrm{mL}\) of 1.010 \(\mathrm{M}\) NaOH for neutralization. Calculate the percentage by mass of calcium carbonate in the rock, assuming that it is the only substance reacting with the HCl solution.

Uranium hexafluoride, UF\(_{6}\), is processed to produce fuel for nuclear reactors and nuclear weapons. UF\(_{6}\) is made from the reaction of elemental uranium with \(\mathrm{ClF}_{3},\) which also produces \(\mathrm{Cl}_{2}\) as a by-product. (a) Write the balanced molecular equation for the conversion of U and \(\mathrm{ClF}_{3}\) into UF \(_{6}\) and \(\mathrm{Cl}_{2}\) . (b) Is this a metathesis reaction? (c) Is this a redox reaction?

Suppose you have a solution that might contain any or all of the following cations: \(\mathrm{Ni}^{2+}, \mathrm{Ag}^{+}, \mathrm{Sr}^{2+},\) and \(\mathrm{Mn}^{2+} .\) Addition of HCl solution causes a precipitate to form. After filtering off the precipitate, \(\mathrm{H}_{2} \mathrm{SO}_{4}\) solution is added to the resulting solution and another precipitate forms. This is filtered off, and a solution of \(\mathrm{NaOH}\) is added to the resulting solution. No precipitate is observed. Which ions are present in each of the precipitates? Which of the four ions listed above must be absent from the original solution?

Antacids are often used to relieve pain and promote healing in the treatment of mild ulcers. Write balanced net ionic equations for the reactions between the aqueous HCl in the stomach and each of the following substances used in various antacids: (a) \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s}),\) (b) \(\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{s})\), \((\mathbf{c}) \mathrm{MgCO}_{3}(s)\), \((\mathbf{d}) \mathrm{NaAl}\left(\mathrm{CO}_{3}\right)(\mathrm{OH})_{2}(s),\) (e) \(\mathrm{CaCO}_{3}(\mathrm{s}).\)

The commercial production of nitric acid involves the following chemical reactions: \begin{equation} \begin{array}{c}{4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)} \\ {2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{NO}_{2}(g)} \\ {3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(I) \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g)}\end{array} \end{equation} (a) Which of these reactions are redox reactions? (b) In each redox reaction identify the element undergoing oxidation and the element undergoing reduction. (c) How many grams of ammonia must you start with to make 1000.0 L of a 0.150 \(\mathrm{M}\) aqueous solution of nitric acid? Assume all the reactions give 100\(\%\) yield.

Consider the following reagents: zinc, copper, mercury (density 13.6 \(\mathrm{g} / \mathrm{mL}\) , silver nitrate solution, nitric acid solution. (a) Given a 500 -mL Erlenmeyer flask and a balloon, can you combine two or more of the foregoing reagents to initiate a chemical reaction that will inflate the balloon? Write a balanced chemical equation to represent this process. What is the identity of the substance that inflates the balloon? (b) What is the theoretical yield of the substance that fills the balloon? (c) Can you combine two or more of the foregoing reagents to initiate a chemical reaction that will produce metallic silver? Write a balanced chemical equation to represent this process. What ions are left behind in solution? (d) What is the theoretical yield of silver?

Bronze is a solid solution of \(\mathrm{Cu}(\mathrm{s})\) and \(\mathrm{Sn}(\mathrm{s})\) ; solutions of metals like this that are solids are called alloys. There is a range of compositions over which the solution is considered a bronze. Bronzes are stronger and harder than either copper or tin alone. (a) \(\mathrm{A} 100.0\) -g sample of a certain bronze is 90.0\(\%\) copper by mass and 10.0\(\%\) tin. Which metal can be called the solvent, and which the solute? (b) Based on part (a), calculate the concentration of the solute metal in the alloy in units of molarity, assuming a density of 7.9 \(\mathrm{g} / \mathrm{cm}^{3}\) . (c) Suggest a reaction that you could do to remove all the tin from this bronze to leave a pure copper sample. Justify your reasoning.

Neurotransmitters are molecules that are released by nerve cells to other cells in our bodies, and are needed for muscle motion, thinking, feeling, and memory. Dopamine is a common neurotransmitter in the human brain. (a) Predict what kind of reaction dopamine is most likely to undergo in water: redox, acid-base, precipitation, or metathesis? Explain your reasoning. (b) Patients with Parkinson's disease suffer from a shortage of dopamine and may need to take it to reduce symptoms. An IV (intravenous fluid) bag is filled with a solution that contains 400.0 mg dopamine per 250.0 mL. of solution. What is the concentration of dopamine in the IV bag in units of molarity? (c) Experiments with rats show that if rats are dosed with 3.0 \(\mathrm{mg} / \mathrm{kg}\) of cocaine (that is, 3.0 mg cocaine per kg of animal mass), the concentration of dopamine in their brains increases by 0.75\(\mu M\) after 60 seconds. Calculate how many molecules of dopamine would be produced in a rat (average brain volume 5.00 \(\mathrm{mm}^{3} )\) after 60 seconds of a 3.0 \(\mathrm{mg} / \mathrm{kg}\) dose of cocaine.

Hard water contains \(\mathrm{Ca}^{2+}, \mathrm{Mg}^{2+},\) and \(\mathrm{Fe}^{2+},\) which interfere with the action of soap and leave an insoluble coating on the insides of containers and pipes when heated. Water softeners replace these ions with \(\mathrm{Na}^{+} .\) Keep in mind that charge balance must be maintained. (a) If 1500 Lof hard water contains 0.020\(M \mathrm{Ca}^{2+}\) and \(0.0040 \mathrm{M} \mathrm{Mg}^{2+},\) how many moles of \(\mathrm{Na}^{+}\) are needed to replace these ions? ( b) If the sodium is added to the water softener in the form of \(\mathrm{NaCl}\) , how many grams of sodium chloride are needed?

Tartaric acid, \(\mathrm{H}_{2} \mathrm{C}_{4} \mathrm{H}_{4} \mathrm{O}_{6}\) , has two acidic hydrogens. The acid is often present in wines and a salt derived from the acid precipitates from solution as the wine ages. A solution containing an unknown concentration of the acid is titrated with NaOH. It requires 24.65 \(\mathrm{mL}\) of 0.2500 \(\mathrm{M}\) NaOH solution to titrate both acidic protons in 50.00 \(\mathrm{mL}\) of the tartaric acid solution. Write a balanced net ionic equation for the neutralization reaction, and calculate the molarity of the tartaric acid solution.

(a) A strontium hydroxide solution is prepared by dissolving 12.50 g of \(\operatorname{Sr}(\mathrm{OH})_{2}\) in water to make 50.00 \(\mathrm{mL}\) of solution. What is the molarity of this solution? (b) Next the strontium hydroxide solution prepared in part (a) is used to titrate a nitric acid solution of unknown concentration. Write a balanced chemical equation to represent the reaction between strontium hydroxide and nitric acid solutions. (c) If 23.9 mL of the strontium hydroxide solution was needed to neutralize a 37.5 mL aliquot of the nitric acid solution, what is the concentration (molarity) of the acid?

A solid sample of \(\mathrm{Zn}(\mathrm{OH})_{2}\) is added to 0.350 \(\mathrm{L}\) of 0.500 \(\mathrm{M}\) aqueous HBr. The solution that remains is still acidic. It is then titrated with 0.500 \(\mathrm{MNaOH}\) solution, and it takes 88.5 mL of the NaOH solution to reach the equivalence point. What mass of \(\mathrm{Zn}(\mathrm{OH})_{2}\) was added to the HBr solution?

(a) By titration, 15.0 \(\mathrm{mL}\) of 0.1008 \(\mathrm{M}\) sodium hydroxide is needed to neutralize a \(0.2053-\mathrm{g}\) sample of a weak acid. What is the molar mass of the acid if it is monoprotic? (b) An elemental analysis of the acid indicates that it is composed of \(5.89 \% \mathrm{H}, 70.6 \% \mathrm{C},\) and 23.5\(\% \mathrm{O}\) by mass. What is composed of \(5.89 \% \mathrm{H}, 70.6 \% \mathrm{C},\) and 23.5\(\% \mathrm{O}\) by mass. What is its molecular formula?

Gold is isolated from rocks by reaction with aqueous cyanide, \(\mathrm{CN} : 4 \mathrm{Au}(s)+8 \mathrm{NaCN}(a q)+\mathrm{O}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow\) \(4 \mathrm{Na}\left[\mathrm{Au}(\mathrm{CN})_{2}\right](a q)+4 \mathrm{NaOH}(a q) .\) (a) \(\mathrm{Which}\) atoms from which compounds are being oxidized, and which atoms from which compounds are being reduced? (b) The \(\left[\mathrm{Au}(\mathrm{CN})_{2}\right]^{-}\) ion can be converted back to \(\mathrm{Au}(0)\) by reaction with \(\mathrm{Zn}(s)\) powder. Write a balanced chemical equation for this reaction. (c) How many liters of a 0.200\(M\) sodium cyanide solution would be needed to react with 40.0 \(\mathrm{kg}\) of rocks that contain 2.00\(\%\) by mass of gold?

A fertilizer railroad car carrying \(34,300\) gallons of commercial aqueous ammonia \((30 \%\) ammonia by mass) tips over and spills. The density of the aqueous ammonia solution is 0.88 \(\mathrm{g} / \mathrm{cm}^{3} .\) What mass of citric acid, \(\mathrm{C}(\mathrm{OH})(\mathrm{COOH})\left(\mathrm{CH}_{2} \mathrm{COOH}\right)_{2},\) (which contains three acidic protons) is required to neutralize the spill? 1 gallon \(=3.785 \mathrm{L} .\)

A sample of 7.75 g of \(\mathrm{Mg}(\mathrm{OH})_{2}\) is added to 25.0 \(\mathrm{mL}\) of 0.200 \(\mathrm{M} \mathrm{HNO}_{3}\) . (a) Write the chemical equation for the reaction that occurs. (b) Which is the limiting reactant in the reaction? (c) How many moles of \(\mathrm{Mg}(\mathrm{OH})_{2}, \mathrm{HNO}_{3},\) and \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) are present after the reaction is complete?

Ritalin is the trade name of a drug, methylphenidate, used to treat attention- deficit/hyperactivity disorder in young adults. The chemical structure of methylphenidate is (a) Is Ritalin an acid or a base? An electrolyte or a nonelectrolyte? (b) A tablet contains a 10.0 -mg dose of Ritalin. Assuming all the drug ends up in the bloodstream and the average man has a total blood volume of 5.0 \(\mathrm{L}\) , calculate the initial molarity of Ritalin in a man's bloodstream. (c) Ritalin has a half-life of 3 hours in the blood, which means that after 3 hours the concentration in the blood has decreased by half of its initial value. For the man in part (b), what is the concentration of Ritalin in his blood after 6 hours?

The mass percentage of chloride ion in a 25.00 -mL. sample of seawater was determined by titrating the sample with silver nitrate, precipitating silver chloride. It took 42.58 \(\mathrm{mL}\) of 0.2997 M silver nitrate solution to reach the equivalence point in the titration. What is the mass percentage of chloride ion in seawater if its density is 1.025 \(\mathrm{g} / \mathrm{mL}\) ?

The arsenic in a \(1.22-\) g sample of a pesticide was converted to \(\mathrm{AsO}_{4}^{3-}\) by suitable chemical treatment. It was then titrated using \(\mathrm{Ag}^{+}\) to form \(\mathrm{Ag}_{3} \mathrm{AsO}_{4}\) as a precipitate. (a) What is the oxidation state of As in AsO \(_{4}^{3-2}(\mathbf{b})\) Name \(\mathrm{Ag}_{3} \mathrm{AsO}_{4}\) by analogy to the corresponding compound containing phosphorus in place of arsenic. (c) If it took 25.0 \(\mathrm{mL}\) of 0.102 \(\mathrm{MAg}^{+}\) to reach the equivalence point in this titration, what is the mass percentage of arsenic in the pesticide?

The U.S. standard for arsenate in drinking water requires that public water supplies must contain no greater than 10 parts per billion \((\mathrm{ppb})\) arsenic. If this arsenic is present as arsenate, AsO \(_{4}^{3-},\) what mass of sodium arsenate would be present in a 1.00 -L sample of drinking water that just meets the standard? Parts per billion is defined on a mass basis as $$\mathrm{ppb}=\frac{\text { g solute }}{\mathrm{g} \text { solution }} \times 10^{9}$$

Federal regulations set an upper limit of 50 parts per million \((\mathrm{ppm})\) of \(\mathrm{NH}_{3}\) in the air in a work environment \([\mathrm{that}\) is, 50 molecules of \(\mathrm{NH}_{3}(g)\) for every million molecules in the air]. Air from a manufacturing operation was drawn through a solution containing \(1.00 \times 10^{2} \mathrm{mL}\) of 0.0105 \(\mathrm{M}\) HCl. The \(\mathrm{NH}_{3}\) reacts with HCl according to: $$\mathrm{NH}_{3}(a q)+\mathrm{HCl}(a q) \longrightarrow \mathrm{NH}_{4} \mathrm{Cl}(a q)$$ After drawing air through the acid solution for 10.0 min at a rate of 10.0 \(\mathrm{L} / \mathrm{min}\) , the acid was titrated. The remaining acid needed 13.1 \(\mathrm{mL}\) of 0.0588 \(\mathrm{M} \mathrm{NaOH}\) to reach the equivalence point. (a) How many grams of \(\mathrm{NH}_{3}\) were drawn into the acid solution? (b) How many ppm of \(\mathrm{NH}_{3}\) were in the air? (Air has a density of 1.20 g/L and an average molar mass of 29.0 \(\mathrm{g} / \mathrm{mol}\) under the conditions of the experiment.) (c) Is this manufacturer in compliance with regulations?