pH Scale of Common Acids and Bases

The pH scale is a crucial parameter in various scientific fields, particularly in chemistry and biology. It measures the hydrogen ion concentration in a solution, indicating its acidity or alkalinity. Alfa Chemistry provides the following pH table of common acids and bases for your review. We hope to help you make it easier to determine the pH of an acid or base (valid for standard conditions at 25 ℃, 1 atm).

Acid	Name	1 mM	10 mM	100 mM
H2CO3	Carbonic Acid	4.68	4.18	3.68
H2CrO4	Chromic Acid	3.03	2.33	2.06
H2MoO4	Molybdic Acid	3.46	2.94	2.43
H2S	Hydroxidegen sulfide	4.97	4.47	3.97
H2Se	Hydroxidegen selenide	3.49	2.93	2.41
H2SeO3	Selenous Acid	3.15	2.47	1.9
H2SeO4	Selenic Acid	2.74	1.83	0.97
H2SO4	Sulfuric Acid	2.75	1.87	1.01
H3AsO3	Arsenious Acid	6.07	5.58	5.09
H3AsO4	Arsenic Acid	3.08	2.31	1.7
H3BO3	Boric Acid	6.12	5.62	5.12
H3Citrate	Citric Acid, C6H8O7	3.24	2.62	2.08
H3PO4	Orthophosphoric Acid	3.06	2.26	1.63
H4SiO4	Silicic Acid	6.4	5.91	5.42
H4SiO4	Silicic Acid (with SiO2(a) precipitation)	6.4	6.26	6.26
HAcetate	Acetic Acid, C2H4O2 (ethanoic Acid)	3.91	3.39	2.88
HBr	Hydroxidebromic Acid	3.01	2.04	1.08
HCl	Hydroxidechloric Acid	3.01	2.04	1.08
HCyanate	Isocyanic Acid, HOCN	3.35	2.76	2.23
HCyanide	Hydroxidecyanic Acid, HCN	6.11	5.62	5.12
HF	Hydroxidefluoric Acid	3.27	2.65	2.12
HFormate	Formic Acid, CH2O2 (methanoic Acid)	3.47	2.91	2.38
HI	Hydroxideiodic Acid	3.01	2.04	1.08
HLactate	Lactic Acid, C3H6O3 (milk Acid)	3.51	2.96	2.44
HNO2	Nitrous Acid	3.28	2.67	2.13
HNO3	Nitric Acid	3.01	2.04	1.08
Base	Name	1 mM	10 mM	100 mM
Ba(OH)2	Barium Hydroxidexide	11.27	12.22	13.08
Be(OH)2	Beryllium Hydroxidexide	7.9	7.9	7.9
Ca(OH)2	Calcium Hydroxidexide (lime, CaO:H2O)	11.27	12.2	12.46
CaCO3	Calcium Carbonate (calcite)	9.91	9.91	9.91
Cd(OH)2	Cadmium Hydroxidexide	9.36	9.36	9.36
Co(OH)2	Cobalt(II) Hydroxidexide	9.15	9.15	9.15
Cr(OH)3	Chromium(III) Hydroxidexide	7.04	7.04	7.04
Cu(OH)2	Copper(II) Hydroxidexide	7.69	7.69	7.69
Fe(OH)2	Iron(II) Hydroxidexide (ferrous Hydroxidexide)	9.45	9.45	9.45
Hg(OH)2	Mercury(II) Hydroxidexide	7.03	7.03	7.03
K2CO3	Potassium Carbonate	10.52	11	11.36
KAcetate	Potassium acetate (CH3COOK)	7.87	8.33	8.75
KHCO3	Potassium Hydroxidegen Carbonate	8.27	8.25	8.13
KOH	Potassium Hydroxidexide (caustic potash)	10.98	11.95	12.88
Mg(OH)2	Magnesium Hydroxidexide	10.4	10.4	10.4
Na2B4O7	Sodium borate (borax)	9.21	9.17	9.05
Na2CO3	Sodium Carbonate (soda ash)	10.52	10.97	11.26
Na2SiO3	Sodium Metasilicate	11	11.91	12.62
Na3PO4	Trisodium Phosphate	10.95	11.71	12.12
CH3COONa	Sodium Acetate	7.87	8.33	8.75
NaHCO3	Sodium Hydroxidegen Carbonate	8.27	8.22	8.02
NaOH	Sodium Hydroxidexide	10.98	11.95	12.88
NH4OH	Ammonium Hydroxidexide (NH3:H2O)	10.09	10.61	11.12
Ni(OH)2	Nickel(II) Hydroxidexide	8.37	8.37	8.37
Pb(OH)2	Lead(II) Hydroxidexide	7.54	7.54	7.54
Sr(OH)2	Strontium Hydroxidexide	11.27	12.22	13.09
Zn(OH)2	Zinc Hydroxidexide	8.88	8.88	8.88

pH Definition

The pH scale ranges from 0 to 14, with 7 being neutral. A pH value below 7 indicates acidity, while a value above 7 signifies alkalinity (basicity). This logarithmic scale is defined by the following equation:

pH=-log[H⁺]

Where [H⁺] is the molar concentration of hydrogen ions in the solution. Due to the logarithmic nature of the scale, each unit change in pH represents a tenfold change in hydrogen ion concentration.

Not all acids and bases react with the same compound at the same rate. Some acid-base reactions occur rapidly and violently, while others proceed more moderately, and some do not react at all. To quantify the strength of acids and bases, we use a universal pH indicator. This indicator changes color depending on the concentration of hydrogen ions (H⁺) present in the solution. Typically, the pH value of acids and bases is used to quantify their strength.

pH of Acids and Bases

Solutions with a pH of 0 are considered strongly acidic. As the pH value increases from 0 to 7, the acidity decreases. Conversely, solutions with a pH of 14 are considered strongly basic, with basicity decreasing as the pH value decreases from 14 to 7. The strength of acids and bases is determined by the number of H⁺ and OH^- ions they produce. Strong acids release more H⁺ ions.

The degree of ionization varies among different acids and bases, affecting their strength. The concentration of hydronium ions (H3O⁺) also determines the strength of an acid. By comparing the concentrations of hydronium ions and hydroxyl ions, we can distinguish between acids and bases:

• For acidic solutions: [H₃O⁺] > [OH^-]
• For neutral solutions: [H₃O⁺] = [OH^-]
• For basic solutions: [H₃O⁺] < [OH^-]

Limitations of the pH Scale

The pH value of a solution does not immediately indicate its relative strength. For example:

• pH is zero for 1N solution of strong acid.
• pH is negative for concentrations 2N, 3N, ION of strong acids.

At higher concentrations, the Hammett acidity function is used instead of pH.

Measuring pH

pH measurement can be performed using various methods, ranging from simple indicators to sophisticated electronic pH meters.

• pH Indicators: These are substances that change color at specific pH values, providing a visual estimate of the solution's pH. Common indicators include litmus paper, phenolphthalein, and bromothymol blue.
• pH Meters: These devices provide precise pH measurements by using a probe to measure the hydrogen ion activity in the solution. Modern pH meters offer high accuracy, digital displays, and the ability to store and analyze data.

Understanding the pH value of acids and bases is fundamental to many scientific disciplines and practical applications. By mastering the principles of pH and its implications, we can better manage and harness the properties of acids and bases to benefit various fields of study and industry.