Chemistry · Acids, Bases and Salts
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Which of the following ions can act both as Bronsted acid and base in solvent water?
- A
CN–
- B
SO42–
- C
HCO3–
- D
PO43–
The correct answer is HCO3–. Bicarbonate is amphiprotic, meaning it can function as both a Bronsted-Lowry acid and a base. It can donate a proton to become carbonate (CO32–) or accept a proton to form carbonic acid (H2CO3). This dual ability is due to its intermediate position in the acid-base conjugate pair hierarchy.
Other ions like CN– and SO42– primarily function as bases under typical conditions in water. PO43– predominantly acts as a base by accepting protons to form HPO42– and H2PO4–, and does not function as an acid under normal aqueous conditions.
The cyanide ion, CN–, primarily acts as a Bronsted-Lowry base by accepting a proton to form HCN, and it does not act as an acid.
The sulfate ion, SO42–, mainly acts as a Bronsted-Lowry base. It accepts protons to form HSO4– but does not readily donate protons.
Bicarbonate, HCO3–, is amphiprotic, meaning it can act both as a Bronsted-Lowry acid and base. It can donate a proton to form CO32– or accept a proton to form H2CO3.
Phosphate, PO43–, primarily acts as a Bronsted-Lowry base, accepting protons to form HPO42– and H2PO4–. It does not act as a Bronsted acid in water.
Tagged under Chemistry · Acids, Bases and Salts · 2015