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Chapter 17: Problem 20

Which of the following solutions is a buffer? (a) A solution made by mixing 100 \(\mathrm{mL}\) of 0.100 \(\mathrm{MCH}_{3} \mathrm{COOH}\) and 50 mL of \(0.100 M \mathrm{NaOH},(\mathbf{b})\) a solution made by mixing 100 \(\mathrm{mL}\) of 0.100 \(\mathrm{M} \mathrm{CH}_{3} \mathrm{COOH}\) and 500 \(\mathrm{mL}\) of 0.100 \(\mathrm{M} \mathrm{NaOH}\) , (c) A solution made by mixing 100 \(\mathrm{mL}\) of 0.100 \(\mathrm{MCH}_{3} \mathrm{COOH}\) and 50 \(\mathrm{mL}\) of \(0.100 \mathrm{M} \mathrm{HCl},\) \((\mathbf{d} ) \) A solution made by mixing of 0.100 \(\mathrm{MCH}_{3} \mathrm{COOK}\) and 50 \(\mathrm{mL}\) of 0.100 \(\mathrm{M} \mathrm{KCl}\) .

Short Answer

Expert verified
The buffer solutions are (a) and (d). Solution (a) is a mixture of 0.100 M CH3COOH and 0.100 M NaOH, forming a weak acid and its conjugate base. Solution (d) is a mixture of 0.100 M CH3COOK and 0.100 M KCl, containing both the weak acid and its conjugate base.

Step by step solution

01

(1) Analyze solution (a)

Solution (a) is a mixture of 0.100 M CH3COOH and 0.100 M NaOH. CH3COOH is a weak acid, and NaOH is a strong base. When these two are mixed, CH3COOH reacts with NaOH, to form its conjugate base CH3COO- and water. As NaOH is a strong base, it will neutralize the CH3COOH and produce CH3COO-, creating a solution containing weak acid and its conjugate base.
02

(2) Analyze solution (b)

Solution (b) is a mixture of 0.100 M CH3COOH and 0.100 M NaOH with a much higher volume of NaOH than in solution (a). Here, the NaOH will completely deprotonate CH3COOH, and there won't be any remaining CH3COOH molecules. Since both the weak acid and its conjugate base are not available, this solution won't act as a buffer.
03

(3) Analyze solution (c)

Solution (c) is a mixture of 0.100 M CH3COOH and 0.100 M HCl. CH3COOH is a weak acid, and HCl is a strong acid. When these two are mixed, they do not react with each other because both are acids. Also, there is no conjugate base present in this solution, meaning it can't be a buffer solution.
04

(4) Analyze solution (d)

Solution (d) is a mixture of 0.100 M CH3COOK and 0.100 M KCl. CH3COOK is a salt of the conjugate base CH3COO- and the weak acid CH3COOH. Since K+ does not react with CH3COO-, both the weak acid and its conjugate base are present in this solution. Therefore, the solution will act as a buffer.
05

(Conclusion)

Based on the analysis, solution (a) and solution (d) can be considered buffer solutions. Solutions (b) and (c) do not have the required weak acid/conjugate base or weak base/conjugate acid pairs and, thus, are not buffer solutions.

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Most popular questions from this chapter

Predict whether the equivalence point of each of the following titrations is below, above, or at \(\mathrm{pH} 7 :(\mathbf{a}) \mathrm{NaHCO}_{3}\) titrated with \(\mathrm{NaOH},(\mathbf{b}) \mathrm{NH}_{3}\) titrated with \(\mathrm{HCl},(\mathbf{c}) \mathrm{KOH}\) titrated with HBr.

Baking soda (sodium bicarbonate, \(\mathrm{NaHCO}_{3}\)) reacts with acids in foods to form carbonic acid (\(\mathrm{H}_{2} \mathrm{CO}_{3}\)), which in turn decomposes to water and carbon dioxide gas. In a cake batter, the \(\mathrm{CO}_{2}(g)\) forms bubbles and causes the cake to rise. (a) A rule of thumb in baking is that 1\(/ 2\) teaspoon of baking soda is neutralized by one cup of sour milk. The acid component in sour milk is lactic acid, \(\mathrm{CH}_{3} \mathrm{CH (\mathrm{OH}) \)\mathrm{COOH}\( .Write the chemical equation for this neutralization reaction. (b) The density of baking soda is 2.16 \)\mathrm{g} / \mathrm{cm}^{3} .\( Calculate the concentration of lactic acid in one cup of sour milk(assuming the rule of thumb applies), in units of mol/L. (One cup \)=236.6 \mathrm{mL}=48\( teaspoons). (c) If 1/2 teaspoon of baking soda is indeed completely neutralized by the lactic acid in sour milk, calculate the volume of carbon dioxide gas that would be produced at 1 atm pressure, in an oven set to \)350^{\circ} \mathrm{F}$ .

Equal quantities of 0.010\(M\) solutions of an acid \(\mathrm{HA}\) and a base \(\mathrm{B}\) are mixed. The \(\mathrm{pH}\) of the resulting solution is \(9.2 .\) (a) Write the chemical equation and equilibrium-constant expression for the reaction between \(\mathrm{HA}\) and \(\mathrm{B}\) . (b) If \(K_{a}\) for \(\mathrm{HA}\) is \(8.0 \times 10^{-5}\) , what is the value of the equilibrium constant for the reaction between \(\mathrm{HA}\) and \(\mathrm{B} ?\) (c) What is the value of \(K_{b}\) for \(\mathrm{B}\) ?

A sample of 0.2140 \(\mathrm{g}\) of an unknown monoprotic acid was dissolved in 25.0 \(\mathrm{mL}\) of water and titrated with 0.0950 \(\mathrm{M}$$ \mathrm{NaOH}\). The acid required 30.0 \(\mathrm{mL}\) of base to reach the equivalence point. (a) What is the molar mass of the acid? (b) After 15.0 \(\mathrm{mL}\) of base had been added in the titration, the pH was found to be \(6.50 .\) What is the \(K_{a}\) for the unknown acid?

Consider a beaker containing a saturated solution of \(\mathrm{CaF}_{2}\) in equilibrium with undissolved \(\mathrm{CaF}_{2}(s)\). Solid \(\mathrm{CaCl}_{2}\) is then added to the solution. (a) Will the amount of solid \(\mathrm{CaF}_{2}\) at the bottom of the beaker increase, decrease, or remain the same? (b) Will the concentration of \(\mathrm{Ca}^{2+}\) ions in solution increase or decrease? (c) Will the concentration of \(\mathbf{F}^{-}\) ions in solution increase or decrease?
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