SAT Subject Test Chemistry

PART 2

REVIEW OF MAJOR TOPICS

CHAPTER 11

Acids, Bases, and Salts

AMPHOTERIC SUBSTANCES

Some substances, such as the HCO₃⁻ ion, the HSO₄⁻ ion, the H₂O molecule, and the NH₃ molecule, can act as either proton donors (acids) or proton receivers (bases), depending upon which other substances they come into contact with. These substances are said to be amphoteric. Amphoteric substances donate protons in the presence of strong bases and accept protons in the presence of strong acids.

Examples are the reactions of the bisulfate ion, HSO₄⁻:

With a strong acid, HSO₄⁻ accepts a proton:

HSO₄⁻(aq)+H⁺(aq) → H₂SO₄(aq)

With a strong acid, HSO₄⁻ donates a proton:

HSO₄⁻(aq)+OH⁻(aq) → H₂O()+SO₄²⁻(aq)