pH of Acids and Bases

The pH Of Various Substances?

Chemistry has three major classifications as acids and bases. These are the essential elements of chemistry to carry out reactions and form water and salt. In our daily life, we use different compounds that are either acids or bases. Daily life examples are milk turning sour into curd because of the presence of lactic acid. It all depends upon the pH of various substances. 

How To Define Acids And Bases?

The two chemical compounds: acids and bases have different definitions according to different people. Arrhenius defined both of them as the ionizing compounds and differentiated acids and bases as:

Arrhenius Theory Of Acids And Bases

According to Arrhenius's theory, when we dissolve a compound in aqueous solution, it releases some ions. Thus he defines his theory on acids and bases. 

Acids: Acids leave H+ ions when dissolved in the solution or water. Further, these ions form H3O+ or hydronium ions when combined with water molecules. 

Bases: Bases are the compounds when dissolved in water leaves OH- ions in the solution.  

Here is the reaction explaining chemical equation of formation of hydronium ions:

HCl(aq)  -> H+ (aq) + Cl-(aq)

In the above reaction, when HCl is dissolved in the aqueous solution, it forms H+ ions. Further, these H+ ions dissolve to form H3O+ ions.

HCl(aq) + H2O(l) -> H3- (aq) + Cl- (aq)

The reaction of base dissolving in water:

NaOH (aq)  -> Na+ (aq) + OH-  (aq)

Acids And Bases- pH Scale

Based on the concentration of hydrogen ions, solutions are classified as basic or acidic. Acidic solutions are the one, which has a higher H+ concentration as compared to water. However, basic solutions are the one, which has lower H+ concentration. The concentration of Hydrogen ion is expressed pH that is calculated as:

pH = -log10 [H+]

The square brackets around the hydrogen ion state the concentration. The concentration of H+ in water is 1x10-7 M, which is the value of 7.0 (neutral pH). However, the concentration of H+ moves away whenever an acid or base is added to a water-based solution. 

In terms of pH, an acid in chemistry is a compound that enhances the concentration of H+ in the solution. In contrast, a base provides OH- ion that combines with H+ and removes them from the solution. As a result, bases are the substances, which increase the pH value, and acids are the substances that decrease the pH value.

The pH scale is generally used to rank the solutions in terms of alkalinity (basicity) and acidity. It ranges from 0 to 14, and most of the solutions fall in this range. 

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The above picture shows that anything below 7.0 in pH scale is acidic, and above 7.0 is basic. 

What pH Values Correspond To Acids And Bases?

Strong Acids:

Generally, acids are substances with a pH value of less than 7.0. The value goes on decreasing as the amount of H+ ion increases in the solution. Strong acids are the substances that release H+ ions rapidly or that are 100% ionizable in the solution. Thus, the strong acids have less pH value, nearly 0 to 1. The lower the pH value, the higher is the concentration of H+ ions in the solution, and hence, stronger is the acid. 

For example,

HCl (aq) -> H+ (aq) + Cl- (aq)

It shows that hydrogen chloride, when dissolved in solution, splits out to give hydrogen and chloride ions. Some other examples of strong acids include hydrobromic acids (HBr), sulphuric acid (H2SO4), and many more.

Strong Bases 

The pH of various substances decides its nature. However, bases are substances with pH values greater than 7.0. The value goes on increasing as the amount of H+ decreases in the solution. Strong bases are those substances that release OH- ion in the solution rapidly. These ions scoop the H+ ion present in the solution, and as a result, increase the pH value of the solution. Thus, strong bases usually have pH values, approximately 13 or 14. 

For example, sodium hydroxide (NaOH) is the strong base that splits in the aqueous solution to produce sodium ion and hydroxide ion. Some other examples of strong bases include potassium hydroxide (KOH), and hydroxides of alkali metals.

Weak Acids

A weak acid is the one that fails to ionize in the solution completely. It releases H+ ion in the low concentrations, and thus pH ranges from 5 to 7. Some of the examples include formic acid (HCOOH), acetic acid (CH3COOH), and many more.

Weak Bases

Weak bases are the substances that do not undergo complete dissociation. As a result, there is a decrease in OH- ion concentration and an increase in pH value. Some of the examples include methylamine and ammonia.