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Chapter 1: Problem 21

A laboratory technician wishes to create a buffered solution with a pH of 5. Which of the following acids would be the best choice for the buffer? (A) \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \quad K_{a}=5.9 \times 10^{-2}\) (B) \(\mathrm{H}_{3} \mathrm{AsO}_{4} \quad K_{a}=5.6 \times 10^{-3}\) (C) \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2} \quad K_{a}=1.8 \times 10^{-5}\) (D) \(\mathrm{HOCl}\) \(\quad K_{a}=3.0 \times 10^{-8}\)

Short Answer

Expert verified
Without the exact calculations, the specific answer cannot be provided. By applying the steps, the pKa of each acid can be determined. The acid that has the pKa value closest to the desired pH of 5 will be the best choice. This would be the short answer upon completing the calculations.

Step by step solution

01

Calculate the pKa of each acid

The pKa is calculated by applying the formula pKa = -log Ka. For each of the acids, calculate the pKa:\n (A) \( \mathrm{pKa} = - \log(5.9 \times 10^{-2}) \) \n (B) \(\mathrm{pKa} = - \log(5.6 \times 10^{-3})\) \n (C) \( \mathrm{pKa} = - \log(1.8 \times 10^{-5}) \) \n (D) \( \mathrm{pKa} = - \log(3.0 \times 10^{-8}) \)
02

Compare the resulting pKa values to the desired pH

After calculating the pKa values, compare each to the desired pH of 5. The acid with a pKa value closest to the desired pH is the best choice.
03

Identify the best acid for the buffer

By checking the calculated pKa values, the acid whose pKa is closest to 5 will be the most appropriate choice. If multiple acids have pKa values equally close to 5, any of them could be the best choice.

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Most popular questions from this chapter

Silver sulfate, \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) , has a solubility product constant of \(1.0 \times 10^{-5} .\) The below diagram shows the products of a precipitation reaction in which some silver sulfate was formed. (Diagram Can't Copy) Which ion concentrations below would have led the precipitate to form? (A) \(\left[\mathrm{Ag}^{+}\right]=0.01 M\left[\mathrm{SO}_{4}^{2-}\right]=0.01 M\) (B) \(\left[\mathrm{Ag}^{+}\right]=0.10 M\left[\mathrm{SO}_{4}^{2-}\right]=0.01 M\) (C) \(\left[\mathrm{Ag}^{+}\right]=0.01 M\left[\mathrm{SO}_{4}^{2-}\right]=0.10 M\) (D) This is impossible to determine without knowing the total volume of the solution.

How many moles of \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) must be added to 500 milliliters of water to create a solution that has a 2 -molar concentration of the Na' ion? (Assume the volume of the solution does not change). (A) 0.5 \(\mathrm{mol}\) (B) 1 \(\mathrm{mol}\) (C) 2 \(\mathrm{mol}\) (D) 5 \(\mathrm{mol}\)

Questions 45-48 refer to the following. Inside a calorimeter, 100.0 \(\mathrm{mL}\) of 1.0 \(\mathrm{M}\) hydrocyanic acid (HCN), a weak acid, and 100.0 \(\mathrm{mL}\) of 0.50 \(\mathrm{M}\) sodium hydroxide are mixed. The temperature of the mixture rises from \(21.5^{\circ} \mathrm{C}\) to \(28.5^{\circ} \mathrm{C}\) . The specific heat of the mixture is approximately \(4.2 \mathrm{J} / \mathrm{g}^{\circ} \mathrm{C},\) and the density is identical to that of water. Identify the correct net ionic equation for the reaction that takes place. (A) \(\mathrm{HCN}(a q)+\mathrm{OH}^{-}(a q) \mapsto \mathrm{CN}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (B) \(\mathrm{HCN}(a q)+\mathrm{NaOH}(a q) \leftrightarrow \mathrm{NaCN}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (C) \(\mathrm{H}^{+}(a q)+\mathrm{OH}^{-}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)\) (D) \(\mathrm{H}^{+}(a q)+\mathrm{CN}^{-}(a q)+\mathrm{Na}^{+}(a q)+\mathrm{OH}^{-}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{CN}^{-}(a q)+\mathrm{Na}^{+}\) (aq)

$$\mathrm{Br}_{2}(g)+\mathrm{I}_{2}(g) \leftrightarrow 2 \mathrm{IBr}(g)$$ At \(150^{\circ} \mathrm{C},\) the equilibrium constant, \(K_{c},\) for the reaction shown above has a value of \(300 .\) This reaction was allowed to reach equilibrium in a sealed container and the partial pressure due to IBr(g) was found to be 3 atm. Which of the following could be the partial pressures due to \(\operatorname{Br}_{2}(g)\) and \(I_{2}(g)\) in the container? \(\begin{array}{lll}{} & {\operatorname{Br}_{2}(g)} & {\mathrm{I}_{2}(g)} \\\ {\text { (A) }} & {0.1 \mathrm{atm}} & {0.3 \mathrm{atm}} \\ {\text { (B) }} & {0.3 \mathrm{atm}} & {1 \mathrm{atm}} \\ {\text { (C) }} & {1 \mathrm{atm}} & {1 \mathrm{atm}} \\ {\text { (D) }} & {1 \mathrm{atm}} & {3 \mathrm{atm}}\end{array}\)

A sample of a compound known to consist of only carbon, hydrogen, and oxygen is found to have a total mass of 29.05 g. If the mass of the carbon is 18.02 g and the mass of the hydrogen is 3.03 g, what is the empirical formula of the compound? (A) \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}\) (B) \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\) (C) \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}_{3}\) (D) \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}_{2}\)
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