The PH is a scale that measures the acidity or alkalinity of a solution . Based on its value may be classified as acid (0

ph-solution

In case, however, it is not possible to obtain with it the litmus paper or the solution (for example in a test) one must necessarily resort to mathematical calculation , using a calculator (given the complexity of the calculations) and a table acidity , which allows to discover the values ​​relating to each individual element of the table periodic (therefore solutions with more elements are not present inside). The procedure varies according to the compound that we are going to analyze and this distinction is mainly based on the capacity of dissociation , or to what can liberate during merge with other elements. They say those which dissociate little weak, strong those, instead, will dissociate completely or almost completely.

If it is a weak acid , first of all you need to know its molar concentration before dissociation. If we denote by x the amount of acid that dissociates, with the constant ka acidic then the formula will be: Ka = (x * x) / ( Ca-x ) ​​or Ka = x ^ 2 / (Ca-x); given we’re talking about a weak acid, then the assumption Ca-x we can write as Ca (since x is very small). The formula then becomes x ^ 2 / approx. X can also be written as [H +], or ion hydrogenated and then exits the formula Ka = [H +] ^ 2/Ca. Knowing the Ka and Ca, just apply the inverse of the square root formula to get the h, ie [H +] = root (Ka * Ca). Since the pH of a logarithm, calculated from the above formula we can get it by PH = 1/2 * ( pKa – log Ca). For weak bases the procedure is analogous, with the only difference that will become Ka and Kb indicate the basic constant, while Cb will always be the constant molar before dissociation. To calculate the PH of the solution, if this is a basic solution (where there is a strong base) must make PH = 14 – PH acid, otherwise, if there is a strong acid, the pH will be given by-log (ka).