Name: ph scale in everyday solutions
Uploaded: 2026-06-01T06:27:40.370Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.3.1

The potential of hydrogen, or pH, points to a solution&#x27;s acidity or basicity&#x2014; properties based on the concentration of hydronium ions, formed when water molecules gain an extra proton.
 
 The pH of a solution is the negative logarithm of its hydronium ion concentration. For example, a solution with 1 &#xD7; 10&#x2212;5 M hydronium concentration has a pH of 5.
 
 pH values commonly range from zero to fourteen and are typically depicted in decreasing order of hydronium ion concentration on a pH scale at a standard temperature of 25&#xB0;C.
 
 Since pH is on a logarithmic scale, a solution of pH 4 has ten times more hydronium ions than a solution with pH 5, which has ten times more hydronium ions than pH 6, and so on.
 
 pH seven is neutral since the water molecules autoionize through proton transfer between two water molecules, producing equal concentrations of hydroxide and hydronium ions.
 
 Coffee has an acidic pH due to the high concentration of hydronium ions.
 
 On the other hand, a low hydronium concentration, as in milk of magnesia, results in higher pH values, indicating a basic solution.
 
 Substances above a pH of seven are basic, while those below are acidic.

La possibilit&#xE9; qu&#x2019;une solution donne ou accepte des ions hydrog&#xE8;ne d&#xE9;termine s&#x2019;il s&#x2019;agit d&#x2019;un acide ou d&#x2019;une base. Les solutions acides donnent des protons, tandis que les bases ou les solutions alcalines peuvent accepter des protons. L&#x2019;eau pure a un nombre &#xE9;gal d&#x2019;ions hydrog&#xE8;ne pour donner des protons et d&#x2019;ions hydroxydes pour les recevoir, ce qui en fait une solution neutre.
 
 Le pH est une mesure de l&#x2019;acidit&#xE9; ou de la basicit&#xE9; d&#x2019;une solution &#xE0; base d&#x2019;eau, d&#xE9;termin&#xE9;e par la concentration en ions hydrog&#xE8;ne. Dans un litre d&#x2019;eau pure, il y a 1 x 10-7 moles d&#x2019;ions hydrog&#xE8;ne. Cependant, la gamme &#xE9;tendue des concentrations en ions hydrog&#xE8;ne pr&#xE9;sentes dans les solutions aqueuses rend la mesure du pH en moles encombrante. Ainsi, une &#xE9;chelle de pH a &#xE9;t&#xE9; mise au point dans laquelle les moles d&#x2019;ions d&#x2019;hydrog&#xE8;ne sont converties en utilisant le logarithme d&#xE9;cimal n&#xE9;gatif. Le pH de l&#x2019;eau pure est donc de 7, repr&#xE9;sentant une solution neutre. La plupart des solutions ont un pH entre 0 et 14, mais certaines solutions comme le carborane (avec un pH de -18) l&#x27;exc&#xE8;dent. Un litre de carborane poss&#xE8;de 1 x 1018 moles d&#x2019;ions d&#x2019;hydrog&#xE8;ne.
 
 Lorsque les ions hydrog&#xE8;ne libres et non li&#xE9;s s&#x2019;accumulent comme avec le carborane, la solution est acide, et la valeur du pH tombe en dessous de 7. Le caf&#xE9;, le jus de citron et l&#x2019;acide gastrique (sucs digestifs) sont des solutions acides, avec des pH respectivement autour de 4,5, de 2,5 et de 1,5.
 
 Les solutions avec des valeurs de pH sup&#xE9;rieures &#xE0; 7 ont des concentrations d&#x2019;ions hydrog&#xE8;ne plus faibles et elles sont alcalines. Dans ces solutions, les ions hydrog&#xE8;ne vont se lier &#xE0; d&#x2019;autres constituants, comme les groupes hydroxyles. Cela diminue le nombre total d&#x2019;ions hydrog&#xE8;ne libres et augmente la valeur du pH. L&#x2019;eau sal&#xE9;e et l&#x2019;eau savonneuse sont des exemples de solutions alcalines, avec des pH respectivement d&#x2019;environ 8 et 12.
 
 Les tampons emp&#xEA;chent les grandes variations de pH en absorbant ou en lib&#xE9;rant des ions hydrog&#xE8;ne. &#xC9;tant donn&#xE9; que la plupart des fonctions biologiques se produisent dans des conditions de pH presque neutres, environ de 7,35 &#xE0; 7,45, les tampons sont essentiels. Par exemple, le sang devient acide avec trop de dioxyde de carbone. Le bicarbonate agit comme un tampon et ram&#xE8;ne le sang &#xE0; un pH hom&#xE9;ostatique. Le bicarbonate est &#xE9;galement utilis&#xE9; pour tamponner le chyme car il se d&#xE9;place de l&#x2019;estomac &#xE0; l&#x2019;intestin gr&#xEA;le. Sans cela, l&#x2019;acidit&#xE9; de la nourriture dig&#xE9;r&#xE9;e endommagerait la muqueuse de l&#x2019;intestin.

The potential of hydrogen (pH) is a measure of the acidity or basicity of a water-based solution determined by the concentration of hydronium ions (H3O+). ...

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Education

Enseignement

JoVE Core

Biology

Biologie

Fundamentals

Fondamentaux

Chemistry of Life

La chimie de la vie

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

ph scale in everyday solutions

pH measures how acidic or basic a water-based solution is. It depends on the concentration of hydronium ions, H3O+, in the solution. In one liter of pure water at neutral pH, there are 1×10−7 moles of hydronium ions.

Because hydronium ion levels can vary over a very wide range, measuring pH directly in moles is not practical. The pH scale converts hydronium ion concentration into a negative logarithm. Pure water has a pH of 7 and is neutral. Most solutions fall between 0 and 14, but some, such as carborane, can go beyond that range. Carborane has a pH of −18, and one liter contains 1×1018 moles of hydrogen ions.

As hydronium ions increase, pH drops below 7 and the solution becomes acidic. Coffee has a pH of about 4.5. Lemon juice is around 2.5, and gastric acid, or digestive juices, is around 1.5. These examples show how stronger acidity matches a lower pH.

Solutions with pH above 7 are alkaline. They have a lower hydronium ion concentration. Saltwater has a pH of about 8, and soapy water is around 12. Buffers are solutions that help prevent large changes in pH. They are important because most biological functions happen near neutral pH, about 7.35 to 7.45. Blood stays near an average pH of 7.4 through a buffer system made of carbonic acid, bicarbonate ions, and carbon dioxide. Bicarbonate also helps buffer chyme as it moves from the stomach to the small intestine. Without this protection, the acidity of digested food could damage the intestine lining.

pH Scale in Everyday Solutions

the periodic table and organismal elements

the-periodic-table-and-organismal-elements

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The periodic table helps explain which elements living things need and how those elements are related. Elements are the smallest units of matter that cannot be broken down further by chemical processes. There are 118 known elements, but not all occur naturally, and even fewer are essential for life. Living matter is made mostly of carbon, nitrogen, hydrogen, and oxygen. Together, these elements make up most of the human body and are also found in all life on Earth. Smaller amounts of calcium,...

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covalent bonds

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ionic bonds

Ionic Compounds and Electrolytes

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hydrogen bonds

Hydrogen Bonds in Water

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van der waals interactions

Intermolecular Forces in Polar Solutions

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Electron Geometry and Lone Pairs

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pH measures how acidic or basic a water-based solution is. It depends on the concentration of hydronium ions, H3O+, in the solution. In one liter of pure water at neutral pH, there are 1×10−7 moles of hydronium ions. Because hydronium ion levels can vary over a very wide range, measuring pH directly in moles is not practical. The pH scale converts hydronium ion concentration into a negative logarithm. Pure water has a pH of 7 and is neutral. Most solutions fall between 0 and 14, but some, such...

chemical reactions

Atoms, Bonds, and Chemical Reactions

Chemical reactions rearrange atoms to form new substances. In a reaction, the starting materials are called reactants, and the new substances are called products. The atoms stay the same type and number, but their bonds change, so the substances become different compounds. During a chemical reaction, bonds between atoms break and form again. This means the shared electrons are rearranged. Some reactions happen on their own, while others need an energy source such as heat or light. In biology,...

redox reactions

Electron Transfer in Redox

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cohesion

Water Molecules and Surface Tension

Water molecules stick to each other through cohesion. Water is neutral overall, but it is a polar molecule. The oxygen atom in one water molecule has a partial negative charge, and it can bind with a hydrogen atom that has a partial positive charge in another water molecule. This forms a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules, and these bonds give water its cohesive nature. Cohesion helps water form droplets on a surface. Water does not...

adhesion

Water Climbing by Adhesion

Water can climb or stick to surfaces because of adhesion, which is the attraction between different kinds of molecules. In water, this is easy to see on polar surfaces such as glass or cellulose in plants. The positive hydrogen side of water is more attracted to the negative oxygen in silica than to nearby water molecules. This attraction helps explain capillary action. If a narrow glass tube is placed in a beaker of water, water molecules attach to the tube’s surface and the water level rises.

states of water

Water Phase Changes and Ice Density

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How Specific Heat Affects Temperature

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vaporization

Vaporization, Boiling, and Evaporation

Vaporization changes a liquid into vapor when temperature adds enough kinetic energy to overcome intermolecular forces. It is a surface phenomenon, which means it starts at the liquid’s surface. The energy needed to vaporize a set amount of liquid at a given pressure and constant temperature is called the heat of vaporization. Water shows this process clearly. When liquid water is vaporized, it becomes steam. One way this happens is boiling, which occurs when vapor bubbles form beneath the...

solvents

Water as a Biological Solvent

Water acts as a biological solvent in many living systems. A solvent is a substance, usually a liquid, that dissolves another substance called a solute. When a solvent and a solute mix, they form a solution, which is a uniform mixture of both parts. Water is called a universal biological solvent because its polar structure helps it dissolve many other polar compounds. Polarity means that one side of the molecule has a slight positive charge and the other side has a slight negative charge.

carbon skeletons

Carbon Backbones in Biomolecules

Carbon backbones give biological molecules their structure and flexibility. Living things are built from macromolecules that contain carbon atoms, and organic compounds are defined by a carbon backbone. Carbon is tetravalent, so each carbon atom can bond with four other atoms. Its valence electrons are stable, so carbon rarely becomes an ion. As carbon chains get longer, they can form ring structures, double bonds, and branching side chains. Carbon-carbon bonds create the carbon skeleton.

key terms and concepts

Learn how pH links hydronium ions to acids, bases, and buffers. Explore examples like coffee, lemon juice, blood, saltwater, and soapy water.

pH Scale in Everyday Solutions | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

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La collection JoVE Core Biologie donne vie à la biologie à travers plus de 300 leçons vidéos animées concises et faciles à comprendre qui expliquent les concept clés de la biologie, mais aussi plus de 150 vidéos de scientifiques à l'action effectuant des expériences de recherche dans des laboratoires modernes.

Pennsylvania State Academic Standards

Earth and Space Science

3.3.9-12.K

Minnesota Academic Standards in Science

Chemistry

1.2.1 9L.4.2.2.1

Alabama Course of Study Science

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9-12.B.1.4.b

Florida Department of Education

High School

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pH Scale in Everyday Solutions

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