Lactic acid is a weak acid found in milk. Its calcium salt is a source of calcium for growing animals. A saturated solution of this salt, which we can represent as (Ca(Lact)2) has a [Ca2+]=0.26M and a pH=8.40.
Calculate the Ka of lactic acid, assuming the salt is 100% dissociated.

Ka of lactic acid is 8.24 x 10⁻⁴

Explanation:

Given-

[Ca²⁺] = 0.26M

pH = 8.4

Salt is 100% dissociated

Ka = ?

Ca(Lact)₂ = Ca²⁺ + 2 Lact-

[lact⁻ ] = 0.26 x 2

          = 0.52 M

pOH = 14 - 8.40

        = 5.60

[OH⁻] = 10⁻ X 60 = 2.51 x 10⁻⁶ M = [lact⁻]

Kb = Kw/Ka

     =

     = 1.21 x 10⁻¹¹

Ka = Kw/Kb

    =

    = 8.24 x 10⁻⁴

Thus, Ka of lactic acid is 8.24 x 10⁻⁴

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.