#poh value

1.1 what is pH?

pH only refers to the hydrogen ion concentration in acids and bases and is only meaningful when applied to aqueous (water-based) solutions.

acidic solution: pH < 7; c(H3O+) > 10^-7 mol/l

neutral solution: pH = 7; c(H3O+) = c(OH-) = √Kw = 10^-7 mol/l

alkaline solutions: pH > 7; c(H3O+) < 10^-7 mol/l

typically, values of pH range from 0 to 14, although very strong acids may have a negative pH, while very strong bases may have a pH exceeding 14.

pH is an abbreviation for "power of hydrogen".

1.2 what is pOH?

pOH is a measure of hydroxide ion (OH-) concentration and of the alkalinity of a solution.

acidic solution: pOH > 7; c(OH-) < 10^-7 mol/l

neutral solution: pOH = 7; c(H3O+) = c(OH-) = √Kw = 10^-7 mol/l

alkaline solutions: pOH < 7; c(OH-) > 10^-7 mol/l

2. how to calculate pH

definition: pH is the negative logarithm of the molar hydrogen ion concentration.

to calculate the pH of an aqueous solution you need to know the concentration of the hydronium ion in moles per liter (molarity).

pH = -lg {c(H3O+)}

the hydronium ion concentration can be found from the pH by the reverse of the mathematical operation employed to find the pH.

c(H3O+) = 10^-pH or c(H30+) = antilog (-pH)

example:

question: what is the pH of a solution with (H3O+) = 1 x 10^-6 M

pH = -lg (H3O+)

substitute (H3O+) with the concentration in the question.

pH = -lg (1 × 10^-6)

pH = - (-6)

pH = 6

3. how to calculate pOH

definition: pOH is the negative logarithm of the hydroxide-ion concentration.

to calculate the pOH of an aqueous solution you need to know the concentration of the hydroxide ion in moles per liter (molarity).

pOH =  - log {c(OH-)}

the hydroxide ion concentration can be found from the pOH by the reverse mathematical operation employed to find the pOH.

c(OH-) = 10^-pOH or c(OH-) = antilog ( - pOH)

4. relationship between pH and pOH

pH + pOH = 14

at 25°C Kw = c(H3O+) × c(OH-) = 10^-14

if either the pH or the pOH of a solution is known, the other can be quickly calculated.

5.1 what is pKa?

pKa is the negative base-10 logarithm of the acid dissociation constant (Ka) of a solution.

it is used to determine the strength of an acid or acidic solution.

pKa = -log10Ka

the lower the pKa value, the stronger the acid.

Ka = [A-][H3O+] / [HA][H2O]

HA + H2O ⇆ A- + H3O+

simplified: Ka = [A-][H+]/[HA]

HA ⇆ A- + H+

5.2 what is pKb?

pKb is the negative base-10 logarithm of the base dissociation constant (Kb) of a solution.

it is used to determine the strength of a base or alkaline solution.

pKb = -log10Kb

the lower the pKb value, the stronger the base.

Kb = [B+][H2O] / [BH+] [OH-]

BH+ + OH− ⇌ B + H2O

simplified: Kb = [B+][OH-] / [BOH]

BOH− ⇌ B+ + OH-

6. how to calculate pKa

pKa = - log (Ka)

here Ka is the equilibrium constant for the ionization of the acid.

7. calculating Ka from pKa

the Ka for an acid is calculated from the pKa by performing the reverse of the mathematical operation used to find pKa.

Ka = 10^-pKa  or  Ka = antilog ( - pKa)

8. how to calculate pKb

pKb =  - log (Kb)

here Kb is the equilibrium constant for the ionization of a base.

9. calculating Kb from pKb

the Kb for an acid is calculated from the pKb by performing the reverse of the mathematical operation used to find pKb.

Kb = 10-pKb  or  Kb = antilog ( - pKb)