Question

Which two compounds are classified as bases by the Brønsted-Lowry definition, but not by the Arrhenius definition, and why?

a) Sodium hydroxide (NaOH) and potassium hydroxide (KOH), because they dissociate to form hydroxide ions, not hydrogen ions.
b) Ammonia (NH3) and methane (CH4) because they contain hydrogen but do not dissociate to form hydrogen ions.
c) Ammonia (NH3) and boron trifluoride (BF3), because they form a compound through the transfer of an electron pair.
d) Ammonia (NH3) and sodium carbonate (Na2CO3), because they accept hydrogen ions but lack hydroxide ions.

Answer 1

Ammonia (NH3) and sodium carbonate (Na2CO3) are classified as bases by the Brønsted-Lowry definition but not by the Arrhenius definition because they can accept hydrogen ions without containing hydroxide ions. So the correct option is d.

Step-by-step explanation:

The Brønsted-Lowry definition of a base is broader than the Arrhenius definition. According to the Brønsted-Lowry definition, a base is any substance that can accept a proton. Using this definition, the two compounds classified as bases by the Brønsted-Lowry definition, but not by the Arrhenius definition, are ammonia (NH3) and sodium carbonate (Na2CO3). Ammonia accepts a proton to form NH4+, while sodium carbonate can accept a proton, thus functioning as a base despite not having hydroxide ions in its structure. Therefore, the correct answer is (d) Ammonia (NH3) and sodium carbonate (Na2CO3), because they accept hydrogen ions but lack hydroxide ions.

Answer 2

b) Ammonia (NH3) and methane (CH4) because they contain hydrogen but do not dissociate to form hydrogen ions.

Step-by-step explanation:

A substance will be classified as a base according to Arrhenius theory if it produces OH (-) hydroxide ions in water. Ammonia (NH3) is a basic substance, but it is not an Arrhenius base because it does not release hydroxide ions into solution, the same happens with methane (CH4), where all four hydrogens are bound very tightly to the carbon and are not going anywhere.