Problem 37 - Chemistry: An Atoms-Focused Approach

Question

Do all titrations of samples of strong monoprotic acids with solutions of strong bases have the same pH at their equivalence points? Explain why or why not.

Step-by-Step Solution

Answer

Answer: Yes, all titrations of samples of strong monoprotic acids with solutions of strong bases have the same pH at their equivalence points, which is 7. This is because, at the equivalence point, the number of moles of H+ ions from the acid equal the number of moles of OH- ions from the base, producing a neutral solution and having equal [H⁺] and [OH⁻] concentrations.

Step 1: 1. Understanding strong acids and strong bases

Strong acids are chemicals that completely dissociate into their ions when dissolved in water. This results in a high concentration of H+ ions in the solution. Examples of strong acids include hydrochloric acid (HCl), sulphuric acid (H₂SO₄), and nitric acid (HNO₃). Likewise, strong bases completely dissociate into their respective ions when dissolved in water, having a high concentration of OH- ions. Examples of strong bases include sodium hydroxide (NaOH) and potassium hydroxide (KOH).

Step 2: 2. Understanding the equivalence point in a titration

The equivalence point in a titration is the point at which the moles of the titrant (typically a strong base in our case) added are equal to the moles of the analyte (typically a strong monoprotic acid in our case). This means that the reaction between the strong acid and strong base is complete, producing a neutral solution (in the case of a strong monoprotic acid and strong base). At the equivalence point, the number of moles of H+ from the acid equals the number of moles of OH- from the base, forming H2O.

Step 3: 3. Calculating the pH at the equivalence point

To determine the pH at the equivalence point, we need to know the concentration of OH- ions or H+ ions in the solution at that moment. As mentioned before, at the equivalence point, the number of moles of H+ is equal to the number of moles of OH-, which means that the solution is neutral. Since water is produced as a result of the reaction, it is essential to consider the ionization of water: H₂O ⇌ H⁺ + OH⁻ When the solution is neutral, the concentration of H⁺ and OH⁻ ions are equal ([H⁺]=[OH⁻]=1x10^(-7) M), and the pH is calculated as: pH = -log[H⁺] For a neutral solution ([H⁺]=1x10^(-7)), we obtain a pH of 7 at the equivalence point.

Step 4: 4. Answering the question: Do all strong monoprotic acids and strong bases titrations have the same pH at their equivalence points?

Yes, titrations of samples of strong monoprotic acids with solutions of strong bases have the same pH at their equivalence points, which is 7. This is because, at the equivalence point, the number of moles of H+ ions from the acid equal the number of moles of OH- ions from the base, producing a neutral solution and having equal [H⁺] and [OH⁻] concentrations.