Search results
Results From The WOW.Com Content Network
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 ...
A smaller H + concentration means a greater OH − concentration and, therefore, a greater K b and a greater pH. NaOH (s) (sodium hydroxide) is a stronger base than (CH 3 CH 2) 2 NH (l) (diethylamine) which is a stronger base than NH 3 (g) (ammonia). As the bases get weaker, the smaller the K b values become. [1]
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
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.
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 ...
where [H +] is the equilibrium concentration of H +, K a is the acid dissociation constant, C a and C b are the analytical concentrations of the acid and its conjugate base, respectively, and Δ = [H +] − [OH −]. The equation can be solved for [H +] by using the autoionization constant for water, K w, to introduce [OH −] = K w /[H +].
The concentrations of H + and OH − are not independent quantities. Most commonly [OH −] is replaced by K w [H +] −1 in equilibrium constant expressions which would otherwise include hydroxide ion. Solids also do not appear in the equilibrium constant expression, if they are considered to be pure and thus their activities taken to be one.
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 ...