Calculate the pH at the equivalence point for titrating 0.200 M solutions of each of the following bases with 0.200 M HBr: (b) hydroxylamine 1NH2OH2.

Verified step by step guidance

1. Identify the chemical reaction: Hydroxylamine (NH2OH) reacts with hydrobromic acid (HBr) to form NH3OH+ and Br-. The balanced equation is: NH2OH + HBr -> NH3OH+ + Br-.
2. Determine the nature of the species at the equivalence point: At the equivalence point, all NH2OH has reacted to form NH3OH+. This is a weak acid, and its concentration will be the same as the initial concentration of NH2OH, which is 0.200 M.
3. Calculate the pH using the weak acid equilibrium: The pH at the equivalence point is determined by the hydrolysis of NH3OH+. Use the expression for the acid dissociation constant (Ka) of NH3OH+ to find the concentration of H+ ions.
4. Use the relationship between Ka and Kb: Since NH2OH is a weak base, you can find the Ka of NH3OH+ using the relation Ka * Kb = Kw, where Kw is the ion-product constant of water (1.0 x 10^-14 at 25°C).
5. Calculate the pH: Once you have the concentration of H+ ions from the hydrolysis of NH3OH+, use the formula pH = -log[H+] to find the pH at the equivalence point.

Key Concepts

Titration and Equivalence Point

Titration is a quantitative analytical method used to determine the concentration of a solute in a solution. The equivalence point occurs when the amount of titrant added is stoichiometrically equivalent to the amount of substance in the solution being titrated. At this point, the reaction between the acid and base is complete, and the pH of the solution is determined by the properties of the resulting salt and any remaining species.

pH and its Calculation

pH is a measure of the acidity or basicity of a solution, defined as the negative logarithm of the hydrogen ion concentration. At the equivalence point of a titration involving a weak base and a strong acid, the resulting solution may contain the conjugate acid of the weak base, which can affect the pH. The pH can be calculated using the concentration of the conjugate acid and its dissociation constant (Ka).

Hydroxylamine as a Weak Base

Hydroxylamine (NH2OH) is a weak base that can accept protons, forming its conjugate acid, hydroxylammonium (NH3OH+). When titrated with a strong acid like HBr, the hydroxylamine will be converted to its conjugate acid at the equivalence point. The pH at this point will depend on the concentration of the conjugate acid and its ability to donate protons back to the solution, which can be analyzed using its dissociation constant.