What is a strong base vs. a weak base??

Answer 1

A strong base is one with high concentration of OH (Hydroxyl), likewise a weak base is one with low concentration of OH.

Answer 2

A weak base is a relatively stable anion. For example Cl-. A good indicator for base strength is seen by obtaining a pKa of the conjugate acid of the base. The stronger the conjugate acid is, the weaker the base is. Conversely the weaker the acid is, the stronger its conjugate base is. Here are some examples:

HCl + H2O ---> H3O+ + Cl-; pKa -9 hence very strong acid, and Cl- is very weak base
H3O+ + NH3 ---> H2O+ NH4+; pka -2; hence strong acid, and water is a weak base
H2S + H2O ---> H3O+ + HS-; pka 7, hence weak acid, relatively strong base
NH4+ + H2O ---> H3O+ + NH3; pka 9, hence weak acid, relatively strong base
H2O + NH2- ---> NH3 + HO-; pka 16, hence weak acid, relatively strong base
NH3 + CH3Li ---> NH2- + CH4; pka 38, hence very weak acid, and very strong conjugate base
CH4 + HO- ---> CH3Li + H2O; pka 50, hence exceedinly weak acid and exceedingly strong base.
In the series above, the strongest base is CH3-Li+. An the reason is that the base is not very happy carrying the - charge. Next is NH2- which is to the right (N vs C on the periodic table) of CH3- hence it is next strongest base. In general the less electronegative the atom is (that is carrying the minus charge), the stronger a base it will be; -CH3 > -NH2 > -OH > -F.

(Note all oxygen based bases (ex NaOH, or CH3CH2OK) are quite strong, but relative to these two they are considered weak.)

Answer 3

A strong base is NaOH, because it's dissociated into Na+ + OH-. NH3, ammonia, in water is a weak base, because whether you think it's NH4OH or NH3*H2O, it forms only a small amount of NH4+ and OH-.

Answer 4

Strong acids are 100% ionized in aqueous solution to form the hydronium ion, H3O+ (also written as H+(aq)) and an anion. For example, HCl in water ionizes completely:

HCl + H2O → H3O+(aq) + Cl–(aq) [goes to completion]

(or, equivalently, HCl + water → H+(aq) + Cl–(aq) [goes to completion])


There are very few strong acids, but they are extremely important in chemistry since they are excellent sources of H+(aq), a highly reactive ion!

Strong Acid Examples: HCl (hydrochloric acid), HBr (hydrobromic acid), HI (hydroiodic acid), HNO3 (nitric acid), H2SO4 (sulfuric acid), HClO4 (perchloric acid), and a small number of non-metallic oxides which react with water to give a strong acid (eg., SO3(g) + H2O → H2SO4).

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Strong bases are 100% ionized in aqueous solution to form the hydroxide ion, OH–, and a cation. There are very few strong bases, but they are extremely important in chemistry since they are excellent sources of OH–(aq), a highly reactive ion! Typical ionization reactions are


NaOH(s) + water → Na+(aq) + OH–(aq) [goes to completion]

Na2O(s) + H2O → 2 Na+(aq) + 2 OH–(aq) [goes to completion]


Strong Base Examples:

Alkali metal hydroxides and the more soluble alkaline earth hydroxides: NaOH(s) (sodium hydroxide), KOH(s) (potassium hydroxide), Ba(OH)2(s) (barium hydroxide).
Alkali metal oxides and the more soluble alkaline earth oxides: Na2O(s) (sodium oxide), K2O(s) (potassium oxide), BaO(s) (barium oxide).

The less soluble hydroxides and oxides of the alkaline earth cations are weak bases. Since solubility increases for these compounds as you go down Column II, the hydroxides and oxides of Ba2+ and Sr2+ are generally considered strong bases, while those for Ca2+ are on the borderline between strong and weak due to their limited solubility in water.