The image below is the pH scale and lists pH values of some common solutions.
Features of the pH scale:
1. pH = 7.00 defines a 'neutral solution, [H3O+] = [OH-] = 10 -7 M , neither acidic nor basic.
2. The acidic solutions have pH < 7 and basic solutions have pH > 7
3. The more acidic solution ,the lower its pH ; Lemon juice, at pH ~ 2, is much more acidic than acid rain , pH ~ 4.
4. The more basic solution more higher its pH.
5. A change in pH of one unit reflects a tenfold change in hydronium ion concentration.
Another pH scale here shows the range of pH and hydronium ion concentration.
A logarithum scale is useful not only for expressing hydronium on concentration but also for expressing the hydroxide ion concentrations and equilibrium constants.That is the pH defination can be generalized to other quantities;
pOH = -log [OH-]
pH + pOH = 14.00 ( derived from Kw )
Lets see a problem;
Sample problem 1 : A sample of orange juice has a hydrogen ion concentration of 2.9 x 10^-4 M.What is the pH ?Is the solution acidic or basic?
Solution : we solved the pH part in our last tutorial , so we know that the pH of this solution is 3.54
Now, as the pH is less than 7.00 so the solution is acidic .