Question

Classify each of the compounds as an acid or base:

NH₄OH

NaHCO₃   

H₂SO₄

CH₃COOH

CH₃NH₂

Answer 1

First, let us define "acids" and bases:

Arrhenius Acid/Base

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

HCl, H2SO4, H3PO4 à they will donate 1, 2, and 3 protons to solution i.e. H+

Examples of Arrhenius base

NaOH, Ca(OH)2, and; avoid NH3, since it is basic, yet will not donate OH from its NH3 equation.

Bronsted Lowery Acid/Bases

First, let us define Bronsted Lowry acid/base:

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)

Note that, typically conjugate bases/acids are shown in the right (product) side

So, from your reaction:

H2Y- transforms to H3Y; it is gaining and H+, so it is a BASE

H2Z- transforms to HZ2-; it is losing H+, so it is an ACID

then,

H3Y is the conjugate ACID (since it could donate H+ to form H2Y-)

and HZ2- is the conjugate BASE ( since it could accept H+ to form H2Z-)

Lewis Acid/Base

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

Examples of a Lewis base:

Anything that will accept negatively charged species will do, such as halides, complex anions, etc…

Examples of a Lewis acid:

BH3, AlCl3, FeCl3, H+

Now...

NH4OH --> NH4+ + OH- --> Ahrrenius Base

NaHCO3 ---> Na+ HCO3- --> H+ + HCO3- H2CO3 --> Bronsted Lowry Base

H2SO4 --> H++ HSO4- --> Ahrenius acid / Bronsted Lowry Acid

CH3COOH --> CH3COO- H + --> Ahrenius acid / Bronsted Lowry Acid

CH3NH2 --> CH3NH2 + H+ --> CH3NH3+ --> Bronsted Lowry Base