pH of Acid and Base

pH stands for Potential of Hydrogen, which simply means the power of hydrogen in a compound. pH value helps determine the nature of the solution. It helps to define the acidity and basicity of a solution. pH value should be balanced for the proper well-being of the environment and living organisms.

This article will cover information about the pH of acid and base, the pH scale, the calculation of pH value and the importance of pH.

What is pH in Chemistry?

pH is the amount of concentration of hydrogen ions in a solution. It helps to regulate blood functions and digestive functions in the human body and is also responsible for the well-being of the environment. The Danish chemist Soren Peter Lauritz Sorensen introduced the concept of pH in 1909. Earlier, it was denoted by the notation “p_H•“, with H• as a subscript to the lowercase p, which was later revised to pH in 1924.

Abbreviation of pH

The word pH stands for potential of Hydrogen or simple power of hydrogen. It is helpful in determining the nature of the solution in accordance with the concentration of hydrogen ions present in the solution. The pH value is inversely proportional to the concentration of hydrogen in the solution. This means if the concentration of hydrogen increase the ph value will decrease.

pH of Acid and Base

pH value of a solution can be defined according to its ability of dissociation in H⁺ and the relative concentration of hydrogen ions in pure water. According to this, the solutions are classified as acids, bases and neutral. If the concentration of hydrogen in pure water is greater than 1 × 10^-7 M, the solution acidic, if it is less than 1 × 10^-7 M, the solution is termed as basic or alkaline. If the concentration of hydrogen in pure water is exactly 1 × 10^-7 M, the solution will be neutral.

pH of Acids

Acids are molecules that can either donate a proton or can form a covalent bond with an electron pair. They are generally sour in taste and are corrosive in nature. It can turn blue litmus to red. Hydrochloric acid, sulfuric acid, acetic acid, boric acid are few examples of acids. Acids can either be strong or a weak acid. Strong acids dissociates to generate H⁺ more rapidly than weak acids. The strength of acids can be defined by its pH value. The pH value range of 0-6.9 determines the solution to be acidic. Lower the pH value, stronger is the acid. The acid having ph range of 0-4 are termed under strong acids, for example Hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid are strong acids. If the pH value of acids falls under pH range of 4-6.9, the acid can be termed as moderately weak or weak acids, acetic acid, boric acid are few examples for the same.

Few examples of acids along with their pH value are described below:

pH Value	Acid Strength	Example
0	Very strong	Battery Acid
1	strong	Hydrochloric Acid
2	moderately strong	Lemon juice, Vinegar
3	moderately strong	Orange juice, Soda
4	moderately weak	Acid rain, Tomato
5	weak	Banana, Coffee
6	very weak	Milk

pH of Bases

Bases on the other hand, are the molecules that can accept a proton and consists of OH^– ions. They are generally bitter in taste. They are also termed as alkaline. It can turn red litmus to blue. Lubricating grease, Baking soda or baking powder, Soaps, Toothpaste are few examples of bases. Bases are also classified as strong and weak bases. Strong bases dissociates to generate OH^– more rapidly than weak bases, strong bases dissociates into H⁺ in very less amount. The strength of bases can be defined by its pH value. The pH value range of 7.1-14 determines the solution to be basic. Higher the pH value, stronger is the base. The strongest base have a pH value of 14. The bases having ph range of 7.1 – 11 are termed under weak bases, for example: Ammonia (NH₃), Calcium hydroxide (Ca(OH)₂) and Magnesium hydroxide (Mg(OH)₂) . The bases having pH range of 11-14 are termed as strong bases, for example: Sodium hydroxide (NaOH) and Potassium hydroxide (KOH).

Few examples of bases along with their pH value are described below:

pH Value	Basic Strength	Example
8	Very weak	Sea water
9	Weak	Baking soda
10	Moderately weak	Antacid tablets
11	Moderately strong	Soap
12	strong	Ammonia
13	strong	Bleach
14	very strong	Drain cleaner

If the pH value of a solution is 7, the solution is termed as neutral i.e. neither basic nor acidic.

pH scale

pH scale is used to measure acidity and basicity of a solution. It determines the strength of acids and bases. pH scale is a universal indicator that shows different colours at different concentration of hydrogen ions. The value of pH scale ranges from 0-14, this is a standard value taken to measure the pH of various compounds where 0 means strong acid, 14 means strong basic, and 7 means the solution is neutral. The values on pH scale is the logarithmic value of concentration of hydrogen ion.

Nature of a Solution

The nature of a solution can be defined by checking its pH value, the solution can either be basic, acidic or neutral. To check the nature of a solution we have to take a negative logarithmic value of concentration of hydrogen ion in the solution. Following are the possibilities:

• If pH < 7, solution is acidic, the acidity decreases with decrease in value hence pH=0 is the strong acid.
• If ph = 7, the solution is neutral (i.e. neither basic nor acidic).
• If pH > 7, solution is basic, the basicity decreases with increase in value hence pH=14 is the strong base.

Why does a Water Source Change pH?

 The pH of surface water falls under the range 6.5 to 8.5 and groundwater have a pH under range 6.0 to 8.5. The pH value of pure water is 7, that makes it a neutral solution. However, the pH of water can change due to numerous natural factors and human interaction. Natural factors like photosynthesis, respiration can cause a shift in pH level of water. When gases like carbon-dioxide is dissolved in water, it increases the acidity of the water. Various human activities like discharging wastewater in water bodies, agricultural and industrial waste, oil spillage, etc causes water pollution and hence results in change of pH level. Accumulation of various other minerals, pollutants, soil in water can also cause in varying pH levels of water.

How to calculate pH ?

pH means the concentration oh H⁺ ions so to calculate the pH value of an aqueous solution, we have to simply calculate the concentration of the hydrogen ion in moles per liter (molarity). The pH value is calculated by:

pH = – log [H⁺].

Note: pH Calculation of all types of solution i.e. weak acid, weak base, strong acid, strong base and neutral solutions can be done by the above given formula if the concentration of H⁺ is known.

Example: What will be the value of pH of an aqueous solution with [H⁺] = 10^-6.

Solution:

We know,

pH = – log [H⁺]

Here [H⁺] = 10^-6

pH = – log 10^-6

pH = -(-6 log 10)

pH = 6 (as log 10 = 1)

Hence, the value of pH of an aqueous solution with [H⁺] = 10^-6 is 6.

Importance of pH

The importance of pH is mentioned below:

• pH is very essential for the growth of plants, they grow best at the pH value of 7. If the pH value of soil changes it is neutralized by adding acids or bases.
• Blood functions are also affected by the pH value as they help in proper functioning of the body.
• If the pH value is maintained over 5.5, it can prevent tooth decay.
• In our stomach access hydrochloric acid can cause pain and discomfort, to overcome this the pH of hydrochloric acid is increased by adding an antacid (base) which provides relief by decreasing the pain.
• pH is very essential to maintain environmental factors for distinct species in aquatic habitats. Different species flourish within different ranges of pH.
• pH also controls the microbial actions, nutrients value and behaviour of chemicals.

Limitations of pH scale

pH scale has the following limitations:

• pH scale is not useful for very strong acids and bases outside the range of 1-14.
• The relative strength of the solutions is not given by the pH scale
• At higher concentrations of strong acidic solutions (i.e. 2N, 3N, 5N, etc.,) the pH values will be negative.
• Hammett acidity functions are used instead of the pH scale when solutions are at higher concentrations.

pH of Some Common Acid and Base

The pH value of acid and base varies with change in concentration. Hence, under the standard conditions: i.e. 25°C, and 1 atmospheric pressure, the pH value of some common acids and bases at 1 mMol/L, 10 mMol/L, and 100 mMol/L is given below:

pH of Acids Chart

The following chart shows the pH value of some commonly known acids

Acid name	Chemical Formula	1 mMol/L	10 mMol/L	100 mMol/L
Boric Acid	H3BO3	6.12	5.62	5.12
Carbonic Acid	H2CO3	4.68	4.18	3.68
Chromic Acid	H2CrO4	3.03	2.33	2.06
Hydrochloric Acid	HCl	3.01	2.04	1.08
Hydrofluoric Acid	HF	3.27	2.65	2.12
Hydrogen sulfide	H2S	4.97	4.47	3.97
Nitric Acid	HNO3	3.01	2.04	1.08
Nitrous Acid	HNO2	3.28	2.67	2.13
Selenic Acid	H2SeO4	2.74	1.83	0.97
Sulphuric Acid	H2SO4	2.75	1.87	1.01

pH of Bases Chart

The pH of commonly known Bases is mentioned in the below chart:

Base name	Chemical Formula	1 mMol/L	10 mMol/L	100 mMol/L
Ammonium Hydroxide	NH4OH	10.09	10.61	11.12
Barium Hydroxide	Ba(OH)2	11.27	12.22	13.08
Calcium Carbonate	CaCO3	9.91	9.91	9.91
Calcium Hydroxide	Ca(OH)2	11.27	12.20	12.46
Chromium(III) Hydroxide	Cr(OH)3	7.04	7.04	7.04
Iron(II) Hydroxide	Fe(OH)2	9.45	9.45	9.45
Magnesium Hydroxide	Mg(OH)2	10.40	10.40	10.40
Potassium Carbonate	K2CO3	10.52	11.00	11.36
Sodium Hydroxide	NaOH	10.98	11.95	12.88
Zinc Hydroxide	Zn(OH)2	8.88	8.88	8.88

pH of Acids and Bases – FAQs

1. What is full form of pH?

pH stands for Potential of Hydrogen which simply means the power of hydrogen in a compound.

2. What is the pH of Blood?

The pH range for blood is 7.35–7.45. Blood is slightly basic. The average pH of blood maintained by our body is close to 7.40.

3. What are the pH values of Acids and Bases?

• If pH < 7, solution is acidic, the acidity decreases with decrease in value hence pH=0 is the strong acid.
• If pH > 7, solution is basic, the basicity decreases with increase in value hence pH=14 is the strong base.

4. What is the pH of Milk?

The pH of milk falls under range of 6.4 to 6.8, and sometimes 7. Milk is considered slightly acidic to near neutral on the pH scale.

5. What is the pH of HCl?

Hydrochloric acid (HCl) has a pH under range 1-1.6. At 38% concentration, hydrochloric acid has a pH of 1.1

6. What is Buffer Solution?

Buffer Solution is kind of solution which doesn’t change its pH even after adding small amount of acid or base