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.

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+). In one liter of pure water at neutral pH, there are 1&#xD7;10&#x2212;7 moles of hydronium ions. However, the extensive range of hydronium ion concentrations present in water-based solutions makes measuring pH in moles cumbersome. Therefore, a pH scale was developed to convert moles of hydronium ions into the negative logarithm of the hydronium ion concentration.The pH of pure water, 7, represents a neutral solution. Most solutions have a pH between 0 and 14, but some solutions, like carborane (with a pH of &#x2212;18), exceed this. One liter of carborane has 1&#xD7;1018 moles of hydrogen ions.As more hydronium ions accumulate, the pH value of a solution falls below 7. Coffee, lemon juice, and gastric acid (digestive juices) are acidic solutions with pHs around 4.5, 2.5, and 1.5, respectively.Solutions with a pH above 7 are called alkaline, as they have lower hydronium ion concentration. Saltwater and soapy water are examples of alkaline solutions, with pHs of approximately 8 and 12, respectively.Buffers are solutions that can prevent significant changes to pH. Buffers are critical because most biological functions occur in near-neutral pH conditions, approximately 7.35 to 7.45. For example, blood has an average pH of ~7.4, maintained by a buffer system involving carbonic acid (H2CO3), bicarbonate ions (HCO3&#x2013;), and carbon dioxide (CO2).Bicarbonate is also used to buffer chyme as it moves from the stomach to the small intestine. Without it, the acidity of the digested food would damage the lining of the intestine.

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Biology

Fundamentals

Chemistry of Life

KEY TERMS AND CONCEPTS

Learn by watching this video about pH: Acidity and Basicity of Aqueous Solutions at JoVE.com

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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Electronegativity and Covalent Bond Polarity

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Ionic Compounds and Electrolytes

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hydrogen bonds

Hydrogen Bonds in Water

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Intermolecular Forces in Polar Solutions

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Elements, Compounds, and Bonding

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molecular shapes

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

Redox reactions are chemical reactions that involve electron transfer between atoms or molecules. When one particle gains electrons, another must lose them at the same time. That is why oxidation and reduction always happen together. The two roles in a redox reaction are linked. The atom that is oxidized acts as the reducing agent, or reductant. The atom that is reduced acts as the oxidizing agent, or oxidant. A simple way to remember the ideas is OIL-RIG, which means oxidation is losing...

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

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Water Phase Changes and Ice Density

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How Specific Heat Affects Temperature

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vaporization

Vaporization, Boiling, and Evaporation

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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.

biology

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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From Molecules to Organisms: Structures and Processes

9-12.B.1.4.b

Florida Department of Education

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Life Science

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pH Scale in Everyday Solutions

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