Chapter 7

What physical propertics are used for the separation of the components of a mixture by (a) filrration; (b) chromatography; (c) distillation?

Identify the following as homogencous or hcterogeneous mixtures and suggest a technique for scparating their components: (a) gasolinc and motor oil; (b) carbonated water; (c) charcoal and sugar.

A chemist studying the propertics of photographic emulsions needed to prepare \(25.00 \mathrm{~mL}\). of \(0.155 \mathrm{M}\) \(\mathrm{AgNO}_{3}\) (aq). What mass of silver nitrate must be placed into a \(25.00-\mathrm{mL}\) volumctric flask and dissolved and diluted to the mark with water?

(a) A chemist prepared a solution by dissolving \(1.230 \mathrm{~g}\) of \(\mathrm{KCl}\) in enough water to make \(150.0 \mathrm{~mL}\) of solution. What molar concentration of potassium chloride should appear on the label? (b) If the chemist had mistakenly used a 500 -mL. volumetric flask instead of the 150.0-mL flask in (a), what molar concentration of potassium chloride has the chemist actually prepared?

A student investigating the propertics of solutions containing carbonate ions prepared a solution containing \(7.112 \mathrm{~g}\) of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) in a \(250.0-\mathrm{mL}\) volumetric flask. Some of the solution was transferred to a burer. What volume of solution should be dispensed from the buret to provide (a) \(5.112 \times 10^{-3} \mathrm{~mol} \mathrm{Na}_{2} \mathrm{CO}_{3}\); (b) \(3.451 \times 10^{-3} \mathrm{~mol} \mathrm{CO}_{3}^{2-}\) ?

Explain how you would prepare an aqueous solution of \(0.010 \mathrm{M} \mathrm{KMnO}_{4}(\mathrm{aq})\) starting with (a) solid \(\mathrm{KMnO}_{4} ;\) (b) \(0.050 \mathrm{M} \mathrm{KMnO}_{4}\) (aq).

(a) A 12.56-mL sample of \(1.345 \mathrm{M} \mathrm{K}_{2} \mathrm{SO}_{4}(\mathrm{aq})\) is diluted to \(250.0 \mathrm{~mL}\). What is the molar concentration of \(\mathrm{K}_{2} \mathrm{SO}_{4}\) in the diluted solution? (b) A \(25.00-\mathrm{mL}\) sample of \(0.366 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\) is drawn from a reagent bottle with a pipet. The sample is transferred to a \(125.00-\mathrm{mL}\) volumetric flask and diluted to the mark with water. What is the molar concentration of the dilute hydrochloric acid solution?

(a) What volume of a \(0.778 \mathrm{M} \mathrm{Na}_{2} \mathrm{CO}_{3}\) (aq) solution should be diluted to \(150.0 \mathrm{~mL}\) with water to reduce its concentration to \(0.0234 \mathrm{M} \mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{aq})\) ? (b) An experiment requires the use of \(60.0 \mathrm{~mL}\) of \(0.50 \mathrm{M} \mathrm{NaOH}\) (aq). The stockroom assistant can only find a reagent bottle of \(2.5 \mathrm{M} \mathrm{NaOH}\) (aq). How is the \(0.50 \mathrm{M} \mathrm{NaOH}(\) aq \()\) solution to be prepared?

(a) Determine the mass of anhydrous copper(II) sulfate that must be used to prepare \(250 \mathrm{~mL}\) of a \(0.20 \mathrm{M} \mathrm{CuSO}_{4}(\mathrm{aq})\) solution. (b) Determine the mass of \(\mathrm{CuSO}_{4}-5 \mathrm{H}_{2} \mathrm{O}\) that must be used to prepare \(250 \mathrm{ml}\). of a \(0.20 \mathrm{M} \mathrm{CuSO}_{4}(\mathrm{aq})\) solution.

The sulfuric acid solution that is purchased for a stockroom has a molarity of \(17.8\) M; all sulfuric acid solutions for experiments are prepared by dilution of this stock solution. (a) Determine the volume of \(17.8 \mathrm{M}\) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) that must be diluted to \(250 \mathrm{~mL}\) to prepare a \(2.0 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})\) solution. (b) An experiment requires a \(0.50 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})\) solution. The stockroom manager estimates that \(6.0\) L of the acid is needed. What volume of \(17.8 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq})\) must be used for the preparation?

A chemist prepared an aqueous solution by mixing \(2.50 \mathrm{~g}\) of ammonium phosphate trihydrate, \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4} \cdot 3 \mathrm{H}_{2} \mathrm{O}\) and \(1.50 \mathrm{~g}\) of potassium phosphate, \(\mathrm{K}_{3} \mathrm{PO}_{4}\), with \(500 \mathrm{~g}\) of water. (a) Determine the number of moles of formula units of each compound that was measured. (b) How many moles of \(\mathrm{PO}_{4}{\underline{\phantom{xx}}}^{3-}\) are present in solution? (c) Calculate the mass of phosphate ions present in the solution. (d) What is the total mass of the water present in the solution?

To prepare a very dilute solution, it is advisable to perform successive dilutions of a single prepared reagent solution, rather than to wcigh a very small mass or to measure a very small volume of stock chemical. A solution was prepared by transferring \(0.661 \mathrm{~g}\) of \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) to a \(250.0\)-mL volumetric flask and adding water to the mark. A \(1.000-\mathrm{mL}\). sample of this solution. was transferred to a 500 -mL. volumetric flask and diluted to the mark with water. Then \(10.0 \mathrm{~mL}\) of the diluted solution was transferred to a 250 -mL. flask and diluted to the mark with water. (a) What is the final concentration of \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{\text {, in solution? (b) What }}\) mass of \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) is in this final solution? (The answer to the last question gives the amount that would have had to have been weighed out if the solution had been prepared directly.)

What mass (in grams) of anhydrous sohute is needed to prepare each of the following solutions? (a) \(1.0 \mathrm{~L}\) of \(0.10 \mathrm{M} \mathrm{NaCl}(\mathrm{aq}) ;\) (b) \(250 \mathrm{~mL}\) of \(0.10 \mathrm{M}\) \(\mathrm{CaCl}_{2}(\mathrm{aq}) ;\) (c) \(500 \mathrm{~mL}\) of \(0.63 \mathrm{M} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})\).

Describe the preparation of cach solution, starting with the anhydrous solute and warer and using the corrcsponding volumetric flask: (a) \(25.0 \mathrm{~mL}\) of \(6.0 \mathrm{M}\) \(\mathrm{NaOH}(\mathrm{aq}) ;\) (b) \(1.0 \mathrm{~L}\), of \(0.10 \mathrm{M} \mathrm{BaCl}_{2}\) (aq); (c) \(500 \mathrm{~mL}\) of \(0.0010 \mathrm{M} \mathrm{AgNO}_{3}(\mathrm{aq})\).

Calculate the mole fraction of each component in the following solutions: (a) \(2.5 .0 \mathrm{~g}\) of water and \(50.0 \mathrm{~g}\) of ethanol, \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{OH}\); (b) \(25.0 \mathrm{~g}\) of water and \(50.0 \mathrm{~g}\) of methanol, \(\mathrm{CH}_{3} \mathrm{OH}\); (c) a glucowe solution that is \(0.10 \mathrm{~m}\) \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q)\).

Calculate the molality of the solute in each of the following solutions: (a) \(10.0 \mathrm{~g}\) of \(\mathrm{NaCl}\) dissolvcd in \(250 \mathrm{~g}\) water; (b) \(0.48 \mathrm{~mol}\) of \(\mathrm{KOH}\) dissolved in \(50.0 \mathrm{~g}\) water; (c) \(1.94 \mathrm{~g}\) of urea, \(\mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2}\), dissolved in \(200 \mathrm{~g}\) water.

(a) What mass (in grams) of \(\mathrm{NaOH}\) must be mixed with \(250 \mathrm{~g}\) of water to prepare a \(0.22 \mathrm{~m} \mathrm{NaOH}\) solution? (b) Calculate the amount (in moles) of cthylene glycol, \(\mathrm{HOC}_{2} \mathrm{H}_{4} \mathrm{OH}\), that should be added to \(2.0 \mathrm{~kg}\) of water to prepare a \(0.44 \mathrm{~m} \mathrm{HOC}_{2} \mathrm{H}_{4} \mathrm{OH}\) (aq) solution. (c) Determine the amount (in moles) of HCl that must be dissolved in \(500 \mathrm{~g}\) water to prepare a \(0,0010 m\) HClaq) solution.

In a laboratory exercise, a student mixes \(2.5 .0 \mathrm{~g}\) of cthanol, \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{OH}\), with \(150 \mathrm{~g}\) of water. (a) What is the mole fraction of ethanol in the solution? (b) What is the molality of cthanol in the solution?

Nitric acid is purchased from chemical suppliers as a solution that is \(70 \% \mathrm{HNO}_{3}\) by mass. What mass (in grams) of a \(70 \% \mathrm{HNO}_{3}(\mathrm{aq})\) solution is required to prepare \(250 \mathrm{~g}\) of a \(2.0 \mathrm{~m} \mathrm{HNO}_{3}\) (aq) solution? The density of \(70 \% \mathrm{HNO}_{3}(\mathrm{aq})\) is \(1.42 \mathrm{~g} \cdot \mathrm{cm}^{-1}\).