To create aramuseum.orgical equations for water acting as an acid and also as a base.

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Water (H2O) is an amazing compound in plenty of respects. Here, we will think about its capability to behave together an mountain or a base.

In some circumstances, a water molecule will certainly accept a proton and also thus act together a Brønsted-Lowry base. We saw an example in the dissolving of HCl in H2O:

\<\rmHCl + H_2O_(ℓ) \rightarrow H_3O^+_(aq) + Cl^−_(aq) \labelEq1\>

In various other circumstances, a water molecule can donate a proton and also thus act together a Brønsted-Lowry acid. Because that example, in the existence of the amide ion (see example 4 in ar 10.2), a water molecule donates a proton, make ammonia together a product:


In this case, NH2− is a Brønsted-Lowry base (the proton acceptor).

So, depending upon the circumstances, H2O deserve to act as either a Brønsted-Lowry acid or a Brønsted-Lowry base. Water is no the only substance that can react together an mountain in some cases or a base in others, however it is absolutely the most typical example—and the most important one. A substance that deserve to either donate or accept a proton, relying on the circumstances, is called an amphiprotic compound.

A water molecule deserve to act together an mountain or a base also in a sample of pure water. Around 6 in every 100 million (6 in 108) water molecules experience the following reaction:


This procedure is called the autoionization the water (Figure \(\PageIndex1\)) and occurs in every sample that water, even if it is it is pure or component of a solution. Autoionization wake up to some extent in any kind of amphiprotic liquid. (For comparison, liquid ammonia experience autoionization as well, yet only around 1 molecule in a million billion (1 in 1015) reacts with an additional ammonia molecule.)

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Key Takeaway

Water molecules can act as both an acid and also a base, depending on the conditions.