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Chapter 17: Problem 37

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

Short Answer

Expert verified
(a) NaHCO3 titrated with NaOH: At the equivalence point, the pH will be above 7 due to the basic nature of the resulting sodium carbonate salt. (b) NH3 titrated with HCl: At the equivalence point, the pH will be below 7 due to the acidic nature of the resulting ammonium chloride salt. (c) KOH titrated with HBr: At the equivalence point, the pH will be neutral (pH 7) due to the neutral nature of the resulting potassium bromide salt.

Step by step solution

01

(a) NaHCO3 titrated with NaOH

For this titration, sodium bicarbonate (NaHCO3, a weak acid) reacts with sodium hydroxide (NaOH, a strong base). The balanced chemical equation for this reaction is given by: \[ NaHCO_{3}(aq) + NaOH(aq) \rightarrow Na_{2}CO_{3}(aq) + H_{2}O(l) \] At the equivalence point, we have sodium carbonate (Na2CO3) as the final salt. Sodium carbonate is a salt of a strong base and weak acid, and it will hydrolyze in water and lead to a basic solution. Therefore, at the equivalence point, the pH will be above 7.
02

(b) NH3 titrated with HCl

For this titration, ammonia (NH3, a weak base) reacts with hydrochloric acid (HCl, a strong acid). The balanced chemical equation for this reaction is given by: \[ NH_{3}(aq) + HCl(aq) \rightarrow NH_{4}Cl(aq) \] At the equivalence point, we have ammonium chloride (NH4Cl) as the final salt. Ammonium chloride is a salt of a weak base and strong acid, and it will hydrolyze in water and lead to an acidic solution. Therefore, at the equivalence point, the pH will be below 7.
03

(c) KOH titrated with HBr

For this titration, potassium hydroxide (KOH, a strong base) reacts with hydrobromic acid (HBr, a strong acid). The balanced chemical equation for this reaction is given by: \[ KOH(aq) + HBr(aq) \rightarrow KBr(aq) + H_{2}O(l) \] At the equivalence point, we have potassium bromide (KBr) as the final salt. Potassium bromide is a salt of a strong base and strong acid, and it will not hydrolyze in water. Therefore, at the equivalence point, the pH will be neutral, which means it will be at pH 7.

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Most popular questions from this chapter

Which of these statements about the common-ion effect is most correct? (a) The solubility of a salt MA is decreased in a solution that already contains either \(\mathrm{M}^{+}\) or \(\mathrm{A}^{-} .\) (b) Common ions alter the equilibrium constant for the reaction of an ionic solid with water. \((\mathbf{c})\) The common-ion effect does not apply to unusual ions like \(\mathrm{SO}_{3}^{2-} .(\mathbf{d})\) The solubility of a salt MA is affected equally by the addition of either \(\mathrm{A}^{-}\) or a noncommon ion.

Compare the titration of a strong, monoprotic acid with a strong base to the titration of a weak, monoprotic acid with a strong base. Assume the strong and weak acid solutions initially have the same concentrations. Indicate whether the following statements are true or false. (a) More base is required to reach the equivalence point for the strong acid than the weak acid. \((\mathbf{b})\) The \(\mathrm{pH}\) at the beginning of the titration is lower for the weak acid than the strong acid. \((\mathbf{c})\) The \(\mathrm{pH}\) at the equivalence point is 7 no matter which acid is titrated.

Which of the following salts will be substantially more soluble in an \(\mathrm{HNO}_{3}\) solution than in pure water: (a) \(\mathrm{BaSO}_{4}\), (b) \(\mathrm{CuS},\) (c) \(\mathrm{Cd}(\mathrm{OH})_{2}\) (d) \(\mathrm{PbF}_{2}\), (e) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2} ?\)

You are asked to prepare a \(\mathrm{pH}=3.00\) buffer starting from $2.00 \mathrm{~L}\( of \)0.025 \mathrm{M}$ solution of benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)\) and any amount you need of sodium benzoate $\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COONa}\right) .(\mathbf{a})\( What is the \)\mathrm{pH}$ of the benzoic acid solution prior to adding sodium benzoate? (b) How many grams of sodium benzoate should be added to prepare the buffer? Neglect the small volume change that occurs when the sodium benzoate is added.

Write the expression for the solubility-product constant for each of the following ionic compounds: $\mathrm{BaCrO}_{4}, \mathrm{CuS}, \mathrm{PbCl}_{2}\( and \)\mathrm{LaF}_{3} .$
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