Chapter 7

Explain the difference between a strong electrolyte and a weak electrolyte. Is an "insoluble" salt a weak or a strong electrolyte?

What is the Bronsted acid-base theory? What is the Lewis acid-base theory?

What is a conjugate acid? Conjugate base?

Write the ionization reaction of aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\), in glacial acetic acid, and identify the conjugate acid of aniline. Write the ionization reaction of phenol, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\), in ethylene diamine, \(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2},\) and identify the conjugate base of phenol.

Calculate the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of the following strong acid solutions: (a) \(0.020 \mathrm{M} \mathrm{HClO}_{4}\), (b) \(1.3 \times 10^{-4} \mathrm{M} \mathrm{HNO}_{3}\) (c) \(1.2 \mathrm{M} \mathrm{HCl}\). (d) \(1.2 \times 10^{-9} M \mathrm{HCl}\) (e) \(2.4 \times 10^{-7} \mathrm{MHNO}_{3}\)

Calculate the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of the following strong base solutions: (a) \(0.050 \mathrm{M} \mathrm{NaOH},\) (b) \(0.14 M \mathrm{Ba}(\mathrm{OH})_{2},\) (c) \(2.4 \mathrm{M} \mathrm{NaOH}\) (d) \(3.0 \times 10^{-7} \mathrm{M} \mathrm{KOH}\) (e) \(3.7 \times 10^{-3} M \mathrm{KOH}\)

Calculate the hydroxide ion concentration of the following solutions: (a) \(2.6 \times 10^{-5} \mathrm{M} \mathrm{HCl}\) (b) \(0.20 \mathrm{M} \mathrm{HNO}_{3}\), (c) \(2.7 \times 10^{-9} \mathrm{M} \mathrm{HClO}_{4}\), (d) \(1.9 \mathrm{M} \mathrm{HClO}_{4}\)

Calculate the hydrogen ion concentration of the solutions with the following pH values: (a) \(3.47,\) (b) \(0.20,\) (c) \(8.60,\) (d) \(-0.60,\) (e) \(14.35,\) (f) \(-1.25 .\)

Calculate the \(\mathrm{pH}\) and \(\mathrm{pOH}\) of a solution obtained by mixing equal volumes of \(0.10 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) and \(0.30 \mathrm{M} \mathrm{NaOH}\).

Calculate the \(\mathrm{pH}\) of a solution obtained by mixing equal volumes of a strong acid solution of \(\mathrm{pH} 3.00\) and a strong base solution of \(\mathrm{pH} 12.00 .\)

\(V_{a} \mathrm{~mL}\) of a strong acid solution of \(\mathrm{pH} 2.00\) is mixed with \(V_{b} \mathrm{~mL}\) of a strong base solution of \(\mathrm{pH}\) 11.00. Express \(V_{a}\) in terms of \(V_{b}\) if the mixture is neutral. The solution temperature is \(24^{\circ} \mathrm{C}\).

Calculate the hydrogen ion concentration and pH of a neutral solution at \(50^{\circ} \mathrm{C}\left(K_{w}=5.5 \times 10^{-14}\right.\) at \(50^{\circ} \mathrm{C}\) ).

Calculate the \(\mathrm{pOH}\) of a blood sample whose \(\mathrm{pH}\) is 7.40 at \(37^{\circ} \mathrm{C}\)

\(K_{a}\) for acetic acid \(\left(\mathrm{CH}_{3} \mathrm{COOH}\right)\) is \(1.75 \times 10^{-5} . K_{w}\) is \(1.00 \times 10^{-14}\) (a) Find \(K_{b}\) for acetate ion\(\left(\mathrm{CH}_{3} \mathrm{COO}^{-}\right)\) (b) When \(0.1 M\) of sodium acetate \(\left(\mathrm{CH}_{3}\right.\) COONa \()\) dissolves in water at \(24^{\circ} \mathrm{C}\), what is the \(\mathrm{pH}\) of the solution? Assume the ions behave ideally.

The \(\mathrm{pH}\) of a \(0.20 \mathrm{M}\) solution of a primary amine, \(\mathrm{RNH}_{2},\) is \(8.42 .\) What is the \(\mathrm{p} K_{b}\) of the amine?

A monoprotic organic acid with a \(K_{a}\) of \(6.7 \times 10^{-4}\) is \(3.5 \%\) ionized when \(100 \mathrm{~g}\) of it is dissolved in \(1 \mathrm{~L}\). What is the formula weight of the acid?

The \(\mathrm{pH}\) of a \(0.20 \mathrm{M}\) solution of a primary amine, \(\mathrm{RNH}_{2}\), is 8.42 . What is the \(\mathrm{pK}_{b}\) of the amine?

The first proton of sulfuric acid is completely ionized, but the second proton is only partially dissociated, with an acidity constant \(K_{a 2}\) of \(1.2 \times 10^{-2} .\) Calculate the hydrogen ion concentration in a \(0.0100 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) solution.

An amine, \(\mathrm{RNH}_{2}\), has a \(\mathrm{pK}_{b}\) of \(4.20 .\) What is the \(\mathrm{pH}\) of a \(0.20 \mathrm{M}\) solution of the base?

By how much should a \(0.100 M\) solution of a weak acid HA be diluted in order to double its percent ionization? Assume \(C>100 K_{a}\).

Calculate the \(\mathrm{pH}\) of the solution obtained by adding \(12.0 \mathrm{~mL}\) of \(0.25 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\) to \(6.0 \mathrm{~mL}\) of \(1.0 M \mathrm{NH}_{3}\).

Calculate the \(\mathrm{pH}\) of the solution obtained by adding \(20 \mathrm{~mL}\) of \(0.10 \mathrm{M}\) HOAc to \(20 \mathrm{~mL}\) of \(0.10 \mathrm{M}\) \(\mathrm{NaOH}\).

Calculate the \(\mathrm{pH}\) of the solution prepared by adding \(0.10 \mathrm{~mol}\) each of hydroxylamine and hydrochloric acid to \(500 \mathrm{~mL}\) water.

Calculate the \(\mathrm{pH}\) of a \(0.250 \mathrm{M}\) solution of \(\mathrm{NaHCO}_{3}\).

Calculate the \(\mathrm{pH}\) of a solution prepared by mixing \(5.0 \mathrm{~mL}\) of \(0.10 \mathrm{M} \mathrm{NH}_{3}\) with \(10.0 \mathrm{~mL}\) of \(0.020 \mathrm{MHCl}\).

An acetic acid-sodium acetate buffer of \(\mathrm{pH} 5.00\) is \(0.100 \mathrm{M}\) in \(\mathrm{NaOAc}\). Calculate the \(\mathrm{pH}\) after the addition of \(10 \mathrm{~mL}\) of \(0.1 \mathrm{M} \mathrm{NaOH}\) to \(100 \mathrm{~mL}\) of the buffer.

A buffer solution is prepared by adding \(20 \mathrm{~mL}\) of \(0.10 \mathrm{M}\) sodium hydroxide solution to \(50 \mathrm{~mL}\) of \(0.10 M\) acetic acid solution. What is the \(\mathrm{pH}\) of the buffer?

Aspirin (acetylsalicylic acid) is absorbed from the stomach in the free (nonionized) acid form. If a patient takes an antacid that adjusts the \(\mathrm{pH}\) of the stomach contents to 2.95 and then takes two 5 -grain aspirin tablets (total \(0.65 \mathrm{~g}\) ), how many grams of aspirin are available for immediate absorption from the stomach, assuming immediate dissolution? Also assume that aspirin does not change the \(\mathrm{pH}\) of the stomach contents. The \(\mathrm{pK}_{a}\) of aspirin is \(3.50,\) and its formula weight is 180.2 .

Tris(hydroxymethyl)aminomethane \(\left[\left(\mathrm{HOCH}_{2}\right)_{3} \mathrm{CNH}_{2}-\right.\) Tris, or THAM \(]\) is a weak base frequently used to prepare buffers in biochemistry. Its \(K_{b}\) is \(1.2 \times 10^{-6}\) and \(\mathrm{p} K_{b}\) is \(5.92 .\) The corresponding \(\mathrm{p} K_{a}\) is \(8.08,\) which is near the \(\mathrm{pH}\) of the physiological buffers, and so it exhibits good buffering capacity at physiological \(\mathrm{pH}\). What weight of THAM must be taken with \(100 \mathrm{~mL}\) of \(0.50 M \mathrm{HCl}\) to prepare \(1 \mathrm{~L}\) of a \(\mathrm{pH} 7.40\) buffer?

Use the Henderson-Hasselbalch equation to find the value of \(\left[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right] /\left[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COO}^{-}\right]\) in a solution at (a) \(\mathrm{pH} 3.00,\) and (b) \(\mathrm{pH}\) 5.00. For \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}, \mathrm{pK}_{a}\) is 4.20 .

The total phosphate concentration in a blood sample is determined by spectrophotometry to be \(3.0 \times 10^{-3} M .\) If the \(\mathrm{pH}\) of the blood sample is \(7.45,\) what are the concentrations of \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) and \(\mathrm{HPO}_{4}^{2}\) in the blood?

The Stig Johansson pH calculator has been shown to give pH calculations of NIST standard buffers that are within a few thousandths of a \(\mathrm{pH}\) unit of the NIST values. The NIST buffers are given in Table 13.2 in Chapter \(13 .\) Use the calculator in Reference 15 to calculate the ActpH of the NIST phosphate buffer consisting of \(0.025 \mathrm{M} \mathrm{KH}_{2} \mathrm{PO}_{4}\) and \(0.025 \mathrm{M} \mathrm{Na}_{2} \mathrm{HPO}_{4}\) (footnote \(e\) ) at \(50^{\circ} \mathrm{C}\), and compare with the NIST value of \(6.833 .\) Use \(\mathrm{pK}_{w}=13.26, \mathrm{pK}_{1}=2.25\), \(\mathrm{p} K_{2}=7.18,\) and \(\mathrm{p} K_{3}=12.36\) for \(50^{\circ} \mathrm{C} .\) Don't forget to enter the temperature.

Many geochemical processes are governed by simple chemical equilibria. One example is the formation of stalactites and stalagmites in a limestone cave, and is a good illustration of Henry's law. This is illustrated in the diagram below: Rainwater percolates through soil. Due to microbial activity in the soil, the gaseous \(\mathrm{CO}_{2}\) concentration in the soil interstitial space (expressed as the partial pressure of \(\mathrm{CO}_{2}, \mathrm{pCO}_{2}\). in atmospheres), is \(3.2 \times 10^{-2}\) atm, significantly higher than that in the ambient atmosphere \(\left(3.9 \times 10^{-4} \mathrm{~atm} ; \mathrm{CO}_{2}\right.\) concentration in the ambient atmosphere is presently increasing by \(2 \times 10^{-6}\) atm each year, see http://CO2now.org for the current atmospheric \(\mathrm{CO}_{2}\) concentration). Water percolating through the soil reaches an equilibrium (called Henry's law equilibrium) with the soil interstitial \(\mathrm{pCO}_{2}\) as given by Henry's law: $$ \left[\mathrm{H}_{2} \mathrm{CO}_{3}\right]=K_{\mathrm{H}} \mathrm{pCO}_{2}$$ where \(\mathrm{H}_{2} \mathrm{CO}_{3}\) is the aqueous carbonic acid concentration and \(K_{\mathrm{H}}\) is the Henry's law constant for \(\mathrm{CO}_{2}, 4.6 \times 10^{-2} \mathrm{M}\) /atm at the soil temperature of \(15^{\circ} \mathrm{C}\). The \(\mathrm{CO}_{2}\) -saturated water effluent from the soil layer then percolates through fractures and cracks in a limestone layer, whereupon it is saturated with \(\mathrm{CaCO}_{3} .\) This \(\mathrm{CaCO}_{3}\) saturated water drips from the ceiling of the cave. Because of the diurnal temperature variation outside the cave, the cave "breathes": the \(\mathrm{CO}_{2}\) concentration in the cave atmosphere is essentially the same as in ambient air \(\left(3.9 \times 10^{-4} \mathrm{~atm}\right)\) Show that when the water dripping from the ceiling re-equilibrates with the \(\mathrm{pCO}_{2}\) concentration in the cave atmosphere, some of the calcium in the drip water will re-precipitate as \(\mathrm{CaCO}_{3}\), thus forming stalactites and stalagmites. Assume cave temperature to be \(15^{\circ} \mathrm{C}\) as well. At this temperature the successive dissociation constants of \(\mathrm{H}_{2} \mathrm{CO}_{3}\) are: \(K_{a 1}=3.8 \times 10^{-7}\) and \(K_{a 2}=3.7 \times 10^{-11}, K_{w}\) is \(4.6 \times 10^{-15}\) and \(K_{\mathrm{sp}}\) of \(\mathrm{CaCO}_{3}\) is \(4.7 \times 10^{-9}\) See the text website (as well as the Solutions Manual) for a detailed solution of this complex problem. Corresponding Goal Seek calculations are also given on the website.