To write historicsweetsballroom.comical equations for water acting as an acid and as a base.

You are watching: Which compound can act as both a brønsted-lowry acid and a brønsted-lowry base

Water (H2O) is an interesting compound in numerous respects. Here, we will take into consideration its capacity to behave together an acid or a base.

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

< mHCl + H_2O_(ℓ) ightarrow H_3O^+_(aq) + Cl^−_(aq) labelEq1>

In other circumstances, a water molecule deserve to donate a proton and also thus act as a Brønsted-Lowry acid. Because that example, in the presence of the amide ion (see instance 4 in ar 10.2), a water molecule donates a proton, do ammonia together a product:

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

So, depending on the circumstances, H2O deserve to act as either a Brønsted-Lowry acid or a Brønsted-Lowry base. Water is not the only substance that deserve to react as an acid in some situations or a base in others, yet it is definitely the most usual example—and the most crucial one. A substance that have the right to either donate or expropriate a proton, depending on the circumstances, is referred to as an amphiprotic compound.

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

This process is referred to as the autoionization that water (Figure (PageIndex1)) and occurs in every sample of water, even if it is it is pure or part of a solution. Autoionization occurs to some degree in any kind of amphiprotic liquid. (For comparison, fluid ammonia experience autoionization as well, but only about 1 molecule in a million billion (1 in 1015) reaction with another ammonia molecule.)

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Key Takeaway

Water molecules have the right to act as both one acid and also a base, relying on the conditions.