When ammonia is added to water it accepts a proton and thus is proved a base. As water lends ammonia a proton does it make water an acid?
Water (H2O) is an interesting compound in many respects. Here, we will consider its ability to behave as an acid or a base.
In some circumstances, a water molecule will accept a proton and thus act as a Brønsted-Lowry base. We saw an example in the dissolving of HCl in H2O:
HCl + H2O(ℓ) → H3O+(aq) + Cl−(aq) In other circumstances, a water molecule can donate a proton and thus act as a Brønsted-Lowry acid. For example, in the presence of the amide ion , a water molecule donates a proton, making ammonia as a product:
H2O(ℓ) + NH2−(aq) → OH−(aq) + NH3(aq) In this case, NH2− is a Brønsted-Lowry base (the proton acceptor).
So, depending on the circumstances, H2O can act as either a Brønsted-Lowry acid or a Brønsted-Lowry base. Water is not the only substance that can react as an acid in some cases or a base in others, but it is certainly the most common example—and the most important one. A substance that can either donate or accept a proton, depending on the circumstances, is called an amphiprotic compound.
A water molecule can act as an acid or a base even in a sample of pure water. About 6 in every 100 million (6 in 108) water molecules undergo the following reaction:
H2O(ℓ) + H2O(ℓ) → H3O+(aq) + OH−(aq) This process is called the autoionization of water and occurs in every sample of water, whether it is pure or part of a solution. Autoionization occurs to some extent in any amphiprotic liquid. (For comparison, liquid ammonia undergoes autoionization as well, but only about 1 molecule in a million billion (1 in 1015) reacts with another ammonia molecule
Water (H2O) is an interesting compound in many respects. Here, we will consider its ability to behave as an acid or a base.
In some circumstances, a water molecule will accept a proton and thus act as a Brønsted-Lowry base. We saw an example in the dissolving of HCl in H2O:
HCl + H2O(ℓ) → H3O+(aq) + Cl−(aq)In other circumstances, a water molecule can donate a proton and thus act as a Brønsted-Lowry acid. For example, in the presence of the amide ion , a water molecule donates a proton, making ammonia as a product:
H2O(ℓ) + NH2−(aq) → OH−(aq) + NH3(aq)In this case, NH2− is a Brønsted-Lowry base (the proton acceptor).
So, depending on the circumstances, H2O can act as either a Brønsted-Lowry acid or a Brønsted-Lowry base. Water is not the only substance that can react as an acid in some cases or a base in others, but it is certainly the most common example—and the most important one. A substance that can either donate or accept a proton, depending on the circumstances, is called an amphiprotic compound.
A water molecule can act as an acid or a base even in a sample of pure water. About 6 in every 100 million (6 in 108) water molecules undergo the following reaction:
H2O(ℓ) + H2O(ℓ) → H3O+(aq) + OH−(aq)This process is called the autoionization of water and occurs in every sample of water, whether it is pure or part of a solution. Autoionization occurs to some extent in any amphiprotic liquid. (For comparison, liquid ammonia undergoes autoionization as well, but only about 1 molecule in a million billion (1 in 1015) reacts with another ammonia molecule
