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Chapter 14: Problem 174

Calculate the pH of the following solutions: a. 1.2\(M \mathrm{CaBr}_{2}\) b. 0.84$M \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3} \mathrm{NO}_{3}\left(K_{\mathrm{b}} \text { for } \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}=3.8 \times 10^{-10}\right)$ c. 0.57$M \mathrm{KC}_{7} \mathrm{H}_{5} \mathrm{O}_{2}\left(K_{\mathrm{a}} \text { for } \mathrm{HC}_{7} \mathrm{H}_{5} \mathrm{O}_{2}=6.4 \times 10^{-5}\right)$

Short Answer

Expert verified
a. The pH of 1.2 M CaBr2 solution is 7.00. b. The pH of 0.84 M C_6H_5NH_3NO_3 solution is 0.075. c. The pH of 0.57 M KC_7H_5O_2 solution can be calculated using the given Ka value and the formula pH = 14 - pOH.

Step by step solution

01

Identify the nature of the solution

Determine if the solution is acidic, basic, or neutral. This will depend on the nature of the compound present in the solution. a. CaBr2 is a salt derived from a strong base (Ca(OH)2) and a strong acid (HBr), hence the solution will be neutral. b. C6H5NH3NO3 is derived from a weak base (C6H5NH2) and a strong acid (HNO3), hence the solution will be acidic. c. KC7H5O2 is derived from a strong base (KOH) and a weak acid (HC7H5O2), hence the solution will be basic.
02

Calculate H+ or OH- concentrations

Calculate the molar concentrations of H+ or OH- ions depending on whether the compound is acidic or basic. a. For CaBr2, since it is a neutral salt, there is no need to calculate concentrations of H+ or OH- as [H+] = [OH-] = 10^-7 M. b. For C6H5NH3NO3, the acidic solution will have equal concentration of [H+]: 0.84M c. For KC7H5O2, calculate OH- concentration using Kb Kb = ([OH-][C7H5O-])/[HC7H5O2] 6.4*10^-5 = (x *0.57)/(1 - x) Calculate x
03

Calculate pH and pOH

Calculate pH or pOH of the solutions based on whether they contain H+ or OH- ions. a. For CaBr2, [H+] = 10^-7 M, pH = -log(10^-7) = 7.00 b. For C6H5NH3NO3, pH = -log(0.84) ≈ 0.075 c. For KC7H5O2, calculate pOH using [OH-], and then calculate pH. pOH = -log(x) pH = 14 - pOH
04

Report the pH values

Provide the pH values of the given solutions. a. The pH of 1.2 M CaBr2 solution is 7.00. b. The pH of 0.84 M C6H5NH3NO3 solution is 0.075. c. The pH of 0.57 M KC7H5O2 solution can be obtained using the calculations in step 3.

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Most popular questions from this chapter

Which of the following represent conjugate acid-base pairs? For those pairs that are not conjugates, write the correct conjugate acid or base for each species in the pair. a. \(\mathrm{H}_{2} \mathrm{O}, \mathrm{OH}^{-}\) b. \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{SO}_{4}^{2-}\) c. \(\mathrm{H}_{3} \mathrm{PO}_{4}, \mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) d. $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}, \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}$

Phosphoric acid is a common ingredient in traditional cola drinks. It is added to provide the drinks with a pleasant tart taste. Assuming that in cola drinks the concentration of phosphoric acid is \(0.007 M,\) calculate the \(\mathrm{pH}\) of this solution.

For the reaction of hydrazine \(\left(\mathrm{N}_{2} \mathrm{H}_{4}\right)\) in water, $$ \mathrm{H}_{2} \mathrm{NNH}_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{2} \mathrm{NNH}_{3}^{+}(a q)+\mathrm{OH}^{-}(a q) $$ \(K_{\mathrm{b}}\) is \(3.0 \times 10^{-6} .\) Calculate the concentrations of all species and the pH of a \(2.0-M\) solution of hydrazine in water.

Are solutions of the following salts acidic, basic, or neutral? For those that are not neutral, write balanced equations for the reactions causing the solution to be acidic or basic. The relevant \(K_{\mathrm{a}}\) and \(K_{\mathrm{b}}\) values are found in Tables 14.2 and \(14.3 .\) $\begin{array}{ll}{\text { a. } \operatorname{Sr}\left(\mathrm{NO}_{3}\right)_{2}} & {\text { d. } \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{3} \mathrm{ClO}_{2}} \\ {\text { b. } \mathrm{NH}_{4} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}} & {\text { e. } \mathrm{NH}_{4} \mathrm{F}} \\ {\text { c. } \mathrm{CH}_{3} \mathrm{NH}_{3} \mathrm{O} \mathrm{l}} & {\text { f. } \mathrm{CH}_{3} \mathrm{NH}_{3} \mathrm{CN}}\end{array}$

Codeine \(\left(\mathrm{C}_{18} \mathrm{H}_{21} \mathrm{NO}_{3}\right)\) is a derivative of morphine that is used as an analgesic, narcotic, or antitussive. It was once commonly used in cough syrups but is now available only by prescription because of its addictive properties. If the pH of a $1.7 \times 10^{-3}-M\( solution of codeine is 9.59 , calculate \)K_{\mathrm{b}}$ .
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