pH
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pH is a number, usually on a scale of 0 to 14, that shows how acidic or basic a water-based solution is from its concentration of hydrogen ions.
Definition
What is pH?
pH is a measure of how acidic or basic (alkaline) a solution in water is. Formally, it equals minus the base-10 log of the hydrogen ion concentration in moles per liter, written pH = -log[H+]; chemists often write the ion as hydronium, H3O+. Pure water at 25 °C contains equal amounts of hydrogen and hydroxide ions and has a pH of 7, which is neutral. Values below 7 are acidic and values above 7 are basic.
Because the scale is logarithmic, each step of one unit is a tenfold change in hydrogen ion concentration, so a solution at pH 3 is ten times more acidic than one at pH 4. Living things must keep pH within narrow limits, since it alters the charges and shapes of proteins and so the activity of enzymes. Human blood stays close to 7.4, held there by buffers such as the carbonic acid and bicarbonate system, while stomach acid sits at about 1 to 2.
In the lab, pH is measured with a pH meter or estimated with indicator paper. The symbol is usually read as 'power of hydrogen', though the origin of the p is debated.
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Terms that go with it
- EnzymeAn enzyme is a biological catalyst, usually a protein, that speeds up a specific chemical reaction without being used up in the process.
- HomeostasisHomeostasis is the body's ability to keep internal conditions, such as temperature, blood glucose and pH, steady while conditions around it change.
- ProteinA protein is a large molecule made of one or more chains of amino acids, folded into a specific shape that determines its job in the body.
- DigestionDigestion is the process by which the body breaks food down, by chewing, churning and enzymes, into molecules small enough to absorb into the blood.
- Active siteThe active site is the pocket or groove on an enzyme where the substrate binds and the chemical reaction is catalyzed.
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Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 2.2 Water
- OpenStax Chemistry 2e, 14.2 pH and pOH
- USGS Water Science School: pH and Water
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