Question

For each of the following molecules, determine if they are acids or bases in the presence of water AND which definition (Arrhenius, Bronsted-Lowry, or Lewis) applies to each. [Note: Some molecules may fit multiple definitions.]

NO

H₂S

Ca(OH)₂

MgO

(COOH)₂

BCl₃

NH₄⁺

C₅H₅N

Answer 1

Arrhenius acid/base is the first theory on acid/base definitions, it is mostly true for general applications.

Arrhenius acid is any type of substance that will dissociate in water to form hydrogen ions [H+]. That is, an acid increases the concentration of H+ ions in an aqueous solution.

Arrhenius base is any type of substance that will form hydroxide [OH−] ions. It typically must increase pH since OH- increases in concentration.

Examples of Arrhenius acid

Bronsted Lowry acid: any species that will donate H+ (protons) in solution, and makes pH lower (i.e HCl)

Bronsted Lowry base: any species that will accept H+ (protons) in solution, and makes pH higher (NH3 will accept H+ to form NH4+)

Typically, acid/bases are shown in the left (reactants)

when we write the products:

Bronsted Lowery conjugate base = the base formed when the B.L. acid donates its H+ proton ( i.e. HCl -> Cl-

Bronsted Lowery conjugate acid = the acid formed when the B.L. base accept its H+ proton ( i.e. NH4+ has accept H+ proton)

Lewis acid and base theory deals mainly with electron transfer, rather than proton transfer (H+).

A Lewis acid will accept an electron pair

A Lewis base will donate an electron pair

Kowing all thesee... we cna proceed further:

NO --> H2O + NO --> HNO2 + H+ --> ahrrenius acid, brosnted acid

H2S --> Arrhenius; since it donates H+, Bronsted, since it donates H+; lewis

Ca(OH)2 --> ahrrenius base, since it donates OH-

MgO --> MgO + H2O -> Mg(OH)2 + H2 --> if donates OH- then an ahrrenius base

(COOH)2 --> bronsted acid, ahreenius acid, donates H+

BCl3 --> Lewis acid, since it accepts lone pairs

NH4+ --> Arrhenius; since it donates H+, Bronsted, since it donates H+; lewis

C5H5N --> Bronsted base, since it accepts H+