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Chapter 4: Problem 34

State whether each of the following statements is true or false. Justify your answer in each case. (a) \(\mathrm{NH}_{3}\) contains no \(\mathrm{OH}^{-}\) ions, and yet its aqueous solutions are basic. (b) HF is a strong acid. (c) Although sulfuric acid is a strong electrolyte, an aqueous solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) contains more \(\mathrm{HSO}_{4}^{-}\) ions than \(\mathrm{SO}_{4}^{2-}\) ions.

Short Answer

Expert verified
(a) True. Although NH3 does not contain OH- ions, it forms them when dissolved in water, making the solution basic. (b) False. HF is a weak acid, not a strong acid. (c) True. An aqueous solution of H2SO4 contains more HSO4- ions than SO42- ions, even though H2SO4 is a strong electrolyte.

Step by step solution

01

Statement (a): NH3 contains no OH- ions, and yet its aqueous solutions are basic.

This statement is true. Ammonia (NH3) does not contain hydroxide ions (OH-) in its molecular structure. However, when it is dissolved in water, it reacts with water to form ammonium ions (NH4+) and hydroxide ions (OH-). This increases the concentration of OH- ions in the solution, making it basic. The reaction is as follows: NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq) An increase in OH- ion concentration raises the pH of the solution, indicating that it is indeed basic.
02

Statement (b): HF is a strong acid.

This statement is false. Hydrofluoric acid (HF) is a weak acid. Strong acids dissociate completely in water, releasing a high concentration of hydrogen ions (H+) and corresponding anions. HF, on the other hand, is only partially dissociated in water. This leads to a lower concentration of H+ ions compared to strong acids, making HF a weak acid.
03

Statement (c): Although sulfuric acid is a strong electrolyte, an aqueous solution of H2SO4 contains more HSO4- ions than SO42- ions.

This statement is true. Sulfuric acid (H2SO4) is a strong acid and a strong electrolyte that dissociates completely in water. However, it is important to note that it is diprotic, meaning it has two acidic protons that can be donated. When H2SO4 is dissolved in water, it ionizes in two steps: 1. H2SO4(aq) → H+(aq) + HSO4-(aq) 2. HSO4-(aq) ⇌ H+(aq) + SO42-(aq) In the first step, H2SO4 completely dissociates into H+ and HSO4-. But in the second step, HSO4- only partially dissociates into H+ and SO42- because it acts as a weak acid during the second dissociation. Therefore, the concentration of HSO4- ions in an aqueous solution of H2SO4 is greater than the concentration of SO42- ions.

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Most popular questions from this chapter

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