Chapter 14 Problems

20 original chapter problems from Chemistry II, Chapter 6. Review quizzes remain in their original lessons.

Original reading → · Source answers and worked examples →

1. Order the following solution from lowest $pH$ to highest:
   $1M\ NaOH$ Strong Base
   $0.1M\ HNO_3$ $pK_a=-1.30$
   $0.5M\ NH_3$ $pK_b=4.75$
   $0.5M\ CH_3COOH$ $pK_a=4.76$

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2. Reviewed replacement: CO₂(aq)+H₂O(l)⇌H₂CO₃(aq) has hydration equilibrium constant K_h=10⁻²·⁷⁷ in the stated convention. Does K_h determine how quickly hydration occurs?

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3. Typically, we treat Carbonic acid just like any other acid. However, carbonic acid is actually the product of $CO_2$ reacting with $H_2O$. This hydration reaction has a rate constant to produce $H_2CO_3$ of $pK_h=2.77$. Using that value, and the actual $pK_{a1}$ of $H_2CO_3$, which is $3.6$, determine the $pK_{a1}$ of $CO_2$.

   Using the $pK_{a1}$ you calculated in Problem 2, determine the $pH$ of a solution that has 40g of $CO_2$ dissolved into 50L of water. The $pK_{a2}$ of $CO_2=10.33$.

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4. Reviewed replacement: a dilute ideal solution of monoprotic weak acid HA has analytical concentration 0.100 M and pH=3.22 at 25 °C. No other acid/base species are present. Neglect water autoionization. Determine pKₐ.

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5. Three acids are compared in separate beakers. Acid A has a $pK_a=1.3$. Acid B’s conjugate base has a $pK_b=4.44$. A $2M$ solution of Acid C has a $pH=3.3$. Rank the acids from strongest to weakest.

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6. What concentration of $H_3PO_4$ is required for the concentration of $[OH^-]$ to become less than $10^{-13}$?
   $pK_{a1}=2.12$
   $pK_{a2}=7.21$
   $pK_{a3}=12.32$

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7. Calcium Hydroxide dissolves in water, and as it is a strong base, it fully dissociates:
   $Ca(OH)_2\leftrightarrow Ca^{2+}+2OH^-$. It has a $pK_{sp}=5.26$. Determine the $pH$ of a saturated solution of Calcium Hydroxide.

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8. Reviewed replacement: an ideal 25 °C solution has total concentration C=0.00100 M of a stipulated monoprotic weak acid HA with Kₐ=4.30×10⁻⁷. Neglect water autoionization and determine pH. This is an acid-equilibrium model, rather than a prediction for ordinary rainwater.

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9. Sulfuric acid is a diprotic acid, with a strong first dissociation, and a $pK_{a2}=1.99$. If a solution of Sulfuric acid has a $pH = 5.5$, what is the initial concentration of $H_2SO_4$? What mole-percent of the total $H_2SO_4$ exists as $SO_4^{2-}$?

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10. Determine the $pOH$ needed to result in $30\%$ deprotonation of $NH_4^+$, which has a $pK_a=9.25$.

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11. What mass of Hydrogen Chloride gas is needed to lower the $pH$ of 10L of water to the same as a $1.2M$ solution of $HNO_3$, with a $pK_a=-1.4$.

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12. Determine what volume of a $H_3PO_4$ solution with a $pH=3$ is needed to equal the mass of 3L of a $10M$ $NaCl$ solution. Ignore volume increases from addition of solutes.

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13. Reviewed replacement: at 25 °C, an ideal solution contains 0.0100 M completely dissociated KOH. Find its pOH and pH.

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14. A solution of multiple acids is at a $pH$ of 2. Given the $pK_a$’s of the acids, order the acids by % de-protonation.
    Acid A: $pK_a=1.11$
    Acid B: $pK_a=5.32$
    Acid C: $pK_a =-2.15$
    Acid D: $pK_a = 7.55$

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15. $500mL$ of a $3M$ $HCl$ solution is used to dissolve $20g$ of $Mn(OH)_2$. Determine the $pH$ of the solution after all the Manganese Hydroxide is dissolved.

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16. Reviewed replacement: a 20.0 L ideal gas sample is measured at 298.15 K and 1.00 atm. Only its HCl component dissolves into a stipulated final 5.00 L solution, producing pH=2.00 at 25 °C. Treat HCl as fully dissociated; neglect all other reactions. Find HCl mole fraction, using R=0.082057 L atm mol⁻¹ K⁻¹.

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17. What is the concentration of $[SO_4^{2-}]$ in a solution of $0.5M$ $H_2SO_4$?

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18. Cyanate, $NCO^-$ is the conjugate base to isocyanic acid, $HNCO$. $5g$ of Potassium Cyanate ($KNCO$) is dissolved into $500mL$ of water. Determine the $pH$ of the solution.

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19. Reviewed idealized concentration task at 25 °C: compare the pOH of 4.00 M completely dissociated HCl with the pH of 5.00 M completely dissociated NaOH. Treat concentrations as activities only for this formal exercise.

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20. A solution of Phosphoric acid exists as $30\%$ Phosphate. What is the concentration of the Phosphoric acid?

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