pH. Concept and scale

07/05/2026

The online pH simulations on this page will help you better understand what pH is and how it is measured. You will understand the pH scale, what it means for a solution to have an acidic or alkaline pH, and see how the pH of a solution varies depending on the products that make it up.

This Thematic Unit is part of our Chemistry collection

Acid

Substance that has a pH lower than 7 and is capable of releasing hydrogen ions in a solution.

Base

Substance that has a pH higher than 7 and can accept hydrogen ions or release hydroxyl ions.

Buffer Solution

Chemical mixture that has the ability to resist changes in pH when small amounts of acids or bases are added.

Neutralization

Chemical reaction between an acid and a base that produces salt and water, bringing the pH closer to a neutral value (7).

pH

Logarithmic measure indicating the concentration of hydrogen ions in a solution. Its scale typically ranges from 0 (very acidic) to 14 (very basic).

pH Indicator

Chemical substance that changes color depending on the acidity or basicity level of the solution it is in.

pH Meter

Precision electronic instrument used in the laboratory to measure the pH value of a solution using an electrode.

pH Scale

Numerical range used to specify the acidity or basicity of an aqueous solution.

pOH

Logarithmic measure of the concentration of hydroxyl ions in a solution, complementary to pH.

What is pH

The pH is a fundamental measurement in chemistry and biology that indicates the degree of acidity or basicity of a solution. The concept of pH originated in the early 20th century when the Danish chemist Søren Sørensen proposed the term to describe the concentration of hydrogen ions in solution.

pH scale

The pH scale ranges from 0 to 14, where 0 indicates the highest acidity and 14 indicates the highest basicity. The neutral point is at 7, which represents a concentration of hydrogen ions equal to that of hydroxyl ions in solution.

Acidic pH

A pH less than 7 indicates that the solution is acidic and has a higher concentration of hydrogen ions (H⁺), as is the case with lemon juice or vinegar.

Alkaline pH

A pH greater than 7 indicates that the solution is basic, reflecting a lower concentration of H⁺ and a higher presence of hydroxyl ions (OH⁻), as in soap or baking soda.

Each pH unit represents a 10-fold change in the concentration of hydrogen or hydroxyl ions.

Applications of pH

pH is an important measurement in many scientific fields and industrial applications.

pH in chemistry

In chemistry, pH is used to characterize the acidity or basicity of a solution, which can be critical for the synthesis of new compounds and the understanding of chemical reactions.

pH in biology

In biology, pH is critical to the survival and function of cells, as many enzymes and proteins only function in a specific pH range.

pH in medicine

In medicine, pH is a key indicator of the acid-base balance in the body, which is essential for the diagnosis and treatment of various conditions. For example, measuring blood pH allows for the detection of disorders such as acidosis or alkalosis, while urinary pH helps to evaluate kidney function and prevent stones.

pH in the pharmaceutical industry

In the pharmaceutical industry, pH control is essential to ensure the stability and efficacy of drugs, as it influences the solubility and absorption of active ingredients.

pH in the food industry

In the food industry, pH is used to preserve products, control fermentation, and maintain characteristics such as flavor, texture, and microbiological safety.

pH in environmental management

pH is also important in environmental management and water quality conservation.

In summary, the online pH simulations on this page will be extremely helpful in understanding this important concept in chemistry.

Acid

Substance that has a pH lower than 7 and is capable of releasing hydrogen ions in a solution.

Base

Substance that has a pH higher than 7 and can accept hydrogen ions or release hydroxyl ions.

Buffer Solution

Chemical mixture that has the ability to resist changes in pH when small amounts of acids or bases are added.

Neutralization

Chemical reaction between an acid and a base that produces salt and water, bringing the pH closer to a neutral value (7).

pH

Logarithmic measure indicating the concentration of hydrogen ions in a solution. Its scale typically ranges from 0 (very acidic) to 14 (very basic).

pH Indicator

Chemical substance that changes color depending on the acidity or basicity level of the solution it is in.

pH Meter

Precision electronic instrument used in the laboratory to measure the pH value of a solution using an electrode.

pH Scale

Numerical range used to specify the acidity or basicity of an aqueous solution.

pOH

Logarithmic measure of the concentration of hydroxyl ions in a solution, complementary to pH.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

pH simulations

Introduction to pH

Test the pH of everyday liquids such as coffee, saliva, and soap to determine if they are acidic, basic, or neutral. Investigate how adding more of a liquid or diluting it with water affects the pH.

pH Scale

Test the pH of things like coffee, saliva, and soap to determine if each is acidic, basic, or neutral. Display the relative number of hydroxide ions and hydrogen ions in solution. Switch between logarithmic and linear scales. Investigate whether changing the volume or diluting with water affects the pH. Or you can design your own liquid!

Giants of science

“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Marie Curie

1867

–

1934

Marie Curie discovered the elements polonium and radium, introduced the concept of radioactivity, and pioneered nuclear chemistry, demonstrating that atoms were not indivisible

“In life, there is nothing to be afraid of, only to understand”

Gilbert Newton Lewis

1875

–

1946

Gilbert Lewis formulated the chemical bond theory, introduced electron pairs, and contributed to acid-base theory

“Atoms build nature as bricks build a building”

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“Science is the foundation of truth”

Marie Curie

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Marie Curie discovered the elements polonium and radium, introduced the concept of radioactivity, and pioneered nuclear chemistry, demonstrating that atoms were not indivisible

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Test your knowledge

What is pH, and what does this measurement represent in chemistry?

pH is a fundamental measurement in chemistry and biology that indicates the degree of acidity or basicity of a solution. It is based on the concentration of hydrogen ions (H⁺) present in the medium and was introduced in the early twentieth century by the Danish chemist Søren Sørensen. The pH scale ranges from 0 to 14: values below 7 indicate acidity, values above 7 indicate basicity and 7 corresponds to a neutral solution. Each pH unit represents a tenfold change in H⁺ concentration, making the scale logarithmic. pH influences chemical reactions, biological processes and the physical properties of substances. Its control is essential in laboratories, industries, biological systems and environmental applications.

How does the pH scale work, and what information does it provide about a solution?

The pH scale ranges from 0 to 14 and makes it possible to determine whether a solution is acidic, basic or neutral. A pH below 7 indicates acidity and reflects a higher concentration of hydrogen ions (H⁺). A pH above 7 indicates basicity and is associated with a greater presence of hydroxide ions (OH⁻). A value of 7 corresponds to a neutral solution, where the concentrations of H⁺ and OH⁻ are equal. The scale is logarithmic, meaning that a change of one unit represents a tenfold change in ion concentration. This makes small variations in pH have significant effects on chemical reactions, biological processes and industrial systems.

Why is it important to measure pH in everyday life and in science?

Measuring pH is important because many substances change their behavior depending on their acidity or basicity. In daily life, pH affects the taste of foods, the effectiveness of cleaning products and skin care. In science, it helps control chemical reactions, study cellular processes and ensure that medicines and solutions work properly. It is also key in environmental science, since water pH affects ecosystems and drinking‑water quality. Knowing pH helps make safe decisions and better understand how materials and organisms function.

What does it mean for a solution to be acidic or basic?

An acidic solution has a pH below 7 and contains a higher concentration of hydrogen ions (H⁺). Common examples include lemon juice and vinegar. A basic or alkaline solution has a pH above 7 and contains more hydroxide ions (OH⁻), as in soap or baking soda. These differences affect the taste, reactivity and chemical behavior of substances. Understanding whether a solution is acidic or basic helps predict how it will react and how it should be handled.

In which fields is pH used, and why is it so important?

pH is used in chemistry to characterize solutions and control reactions. In biology it determines enzyme activity and cellular processes. In medicine it helps evaluate the body’s acid‑base balance and diagnose conditions such as acidosis or alkalosis. In the food industry it controls fermentation and ensures product safety. In the pharmaceutical industry it affects the stability and absorption of medications. It is also essential in environmental management to assess water and soil quality. Its importance lies in the fact that small pH variations can alter vital and chemical processes.