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Given its greater H + concentration, the formula yields a lower pH value for the weak base. However, pH of bases is usually calculated in terms of the OH − concentration. This is done because the H + concentration is not a part of the reaction, whereas the OH − concentration is. The pOH is defined as:
pOH is sometimes used as a measure of the concentration of hydroxide ions, OH −. By definition, pOH is the negative logarithm (to the base 10) of the hydroxide ion concentration (mol/L). pOH values can be derived from pH measurements and vice-versa. The concentration of hydroxide ions in water is related to the concentration of hydrogen ions by
The concentration of hydroxide ions can be expressed in terms of pOH, which is close to (14 − pH), [note 3] so the pOH of pure water is also close to 7. Addition of a base to water will reduce the hydrogen cation concentration and therefore increase the hydroxide ion concentration (decrease pH, increase pOH) even if the base does not itself ...
2 O (l) + Ind + (aq) + OH − (aq) where "IndOH" stands for the basic form and "Ind + " for the conjugate acid of the indicator. The ratio of concentration of conjugate acid/base to concentration of the acidic/basic indicator determines the pH (or pOH) of the solution and connects the color to the pH (or pOH) value.
C A is the analytical concentration of the acid and C H is the concentration the hydrogen ion that has been added to the solution. The self-dissociation of water is ignored. A quantity in square brackets, [X], represents the concentration of the chemical substance X. It is understood that the symbol H + stands for the hydrated hydronium ion.
The molar concentration of hydronium or H + ions determines a solution's pH according to pH = -log([H 3 O +]/M) where M = mol/L. The concentration of hydroxide ions analogously determines a solution's pOH. The molecules in pure water auto-dissociate into aqueous protons and hydroxide ions in the following equilibrium: H 2 O ⇌ OH − (aq) + H ...
Water samples that are exposed to air will absorb some carbon dioxide to form carbonic acid (H 2 CO 3) and the concentration of H 3 O + will increase due to the reaction H 2 CO 3 + H 2 O = HCO 3 − + H 3 O +. The concentration of OH − will decrease in such a way that the product [H 3 O +][OH −] remains constant for fixed temperature and ...
Since K w = [H +] × [OH –], then both the concentration of H 3 O + and OH – ions equal 10 −7 M (a very small concentration). In neutral water, the pH, being the negative decimal logarithm of the H 3 O + concentration, it is 7. Similarly, the pOH is also 7. Each unit decrease in pH indicates a tenfold increase of the H 3 O + concentration.