What is the difference between amphoteric and amphiprotic substances? O Both can act as both acids and bases according to the Bronsted-Lowry definition of acids and bases, but for a substance to be amphiprotic it must be able to donate multiple protons. Both can act as both acids and bases according to the Bronsted-Lowry definition of acids and bases, but for a substance to be amphoteric it must be able to both accept and donate protons. O Both can act as both acids and bases according to the Bronsted-Lowry definition of acids and bases, but for a substance to be amphiprotic it must be able to both accept and donate protons. There is no difference. A potentiometric acid-base titration produced the following result. What can you say about the experimental conditions? pH 14 13 12 11 10 9 8 7 6 5 4 3 2 1 ONA O 0 25 5 75 10 12.5 15 17.5 20 225 25 27.5 30 Volume Added (mL) O Strong base was added from the burette to a flask containing strong acid O Strong acid was added from the burette to a flask containing weak base O Weak base was added from the burette to a flask containing strong acid O Weak acid was added from the burette to a flask containing weak base Which of the following acids could be used to make a buffer of pH 7.0 by adding to the acid a molar excess of its conjugate base in the form of a salt? O hydrogen citrate (pK, = 6.40) and carbonic acid (pk, = 6.37) O hydrogen sulfite (pkg = 7.19) and dihydrogen phosphate (pk = 72) hydrogen citrate (pka = 6.40) and hydrogen sulphite (pk, = 719) ammonium (pk. = 9.25) and pyridinium (pka = 5.25) To make up a buffer of pH 7 from equimolar solutions of sodium dihydrogen phosphate (NaH,PO, PK, of H,PO4 = 7.2) and sodium hydrogen phosphate (Na2HPO4, PK, of HPO42- = 12.38). A larger volume of sodium hydrogen phosphate solution would be required Equal volumes of each solution would be required A larger volume of sodium dihydrogen phosphate solution would be required It’s impossible to say what relative volumes of each solution would be required based on the information supplied Which of the following is a valid conjugate acid/base pair? OH3071 H2O/H20 O HO/H20
The Correct Answer and Explanation is:
Here are the correct answers followed by a detailed 300-word explanation:
Correct Answers:
- Amphoteric vs. Amphiprotic:
- ✅ Both can act as both acids and bases according to the Brønsted–Lowry definition of acids and bases, but for a substance to be amphiprotic it must be able to both accept and donate protons.
- Titration Analysis:
- ✅ Strong base was added from the burette to a flask containing strong acid.
- Buffer at pH 7.0:
- ✅ Hydrogen sulfite (pKa = 7.19) and dihydrogen phosphate (pKa = 7.2).
- Buffer from phosphate salts (pH 7):
- ✅ A larger volume of sodium dihydrogen phosphate solution would be required.
- Valid conjugate acid/base pair:
- ✅ H₂O/OH⁻
Explanation
Amphoteric vs. Amphiprotic:
An amphoteric substance can act as either an acid or a base but is not necessarily limited to the Brønsted–Lowry definition (e.g., ZnO can act as both an acid and a base in Lewis theory). An amphiprotic substance specifically donates and accepts protons (H⁺) under the Brønsted–Lowry framework. Therefore, all amphiprotic substances are amphoteric, but not all amphoteric substances are amphiprotic.
Titration Curve Analysis:
The titration curve shows a rapid pH rise from very low (~2) to very high (~12), centered around pH 7. This sharp equivalence point indicates a strong acid reacting with a strong base. Since the base is being added (increasing pH), the strong base is in the burette, and strong acid is in the flask.
Buffer for pH 7.0:
Buffers are most effective when the pKa is close to the desired pH. Both hydrogen sulfite (pKa 7.19) and dihydrogen phosphate (pKa 7.2) are near pH 7, making them suitable. Others are too far in pKa.
Buffer with Phosphates:
For pH 7, which is lower than the pKa of HPO₄²⁻ (12.38), we need more acid form (NaH₂PO₄) than base form to maintain the buffer at pH 7. So, a larger volume of NaH₂PO₄ is required.
Valid Conjugate Pair:
H₂O/OH⁻ is a valid conjugate acid/base pair: water can donate a proton to become OH⁻ (base). Pairs like “OH3071” or “H₂O/H₂O” are invalid or nonsensical.
