There room several interpretations of what constitutes one acid:

The Arrhenius definition: by the 1884 meaning of Svante Arrhenius (Sweden), an mountain is a material that have the right to release a proton or hydrogen ion (H+).

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The Lewis definition: A Lewis acid is one that deserve to accept a pair of electron and type a coordinate covalent bond.

The Brønsted-Lowry definition: Brønsted suggested that all acid-base reactions involve the transport of one H+ ion, or proton. Water reacts v itself, because that example, by transporting an H+ ion from one molecule to another to kind an H3O+ ion and an OH- ion. According to this theory, an mountain is a "proton donor" and a base is a "proton acceptor."

For currently we will certainly stick through the Brønsted-Lowry definition. And we will now tie the ide of acids and also bases right into equilibrium:

Let"s start by looking in ~ the Ionization of Water:

2H2O(l) H3O+(aq) + OH-(aq)

This reaction walk fit the Brønsted-Lowry an interpretation since one water molecule is acting together an mountain "donating" a proton and also the other is acting together a base "accepting" the proton:


If we currently write this reaction right into an equilibrium expression:


But remember among our rules concerning the composing of equilibrium expressions says that we perform not include solvents (liquids) as their concentration stays pretty consistent during a reaction so the water section of the equation is essentially equal come 1 and thus "disappears".

The resulting equation is given a one-of-a-kind designation KW dubbed the ionization continuous of water:


The worth of this constant at 25oC is 1.0 x 10-14. Together you can see indigenous the very tiny value the KW, water is not very dissociated at room temperature and our assumption that the concentration that water being consistent is a great one.

For pure water, the values of <H3O+> and <OH-> space equal and also thus your values room both 1.0 x 10-7. If over there is an equal amount the acid and also base current in any type of solution, the equipment is dubbed "neutral" and the pH that the solution is 7.

If the mountain concentration is higher than the basic concentration, the equipment is acidic and the pH will certainly be much less than 7. If the base concentration is better than the acid concentration, the systems is simple and the pH will be greater than 7.

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The pH Scale:

The pH that a solution is identified as the negative log10

(NOTE: H+ and H3O+ space interchangeable methods to describe the visibility of proton in solution)

The pOH the a solution is characterized as the negative log10


= 10-pH and also = 10-pOH

The pH that a neutral systems is because of this 7. (-log<1 x 10-7> = 7)

The amount of the pH and also pOH must constantly equal 14. This is because the –log KW = -log(1 x 10-14) = 14.