How can water act as an acid or base?

Answer 1

According to the Brønsted-Lowry theory of acids and bases, an acid is any substance that donates a proton (i.e., an H+ ion) and a base is any substance that accepts a proton.

In certain circumstances, water donates a proton to a base and becomes hydroxide (OH-). Since it is donating a proton, water acts as an acid.

ClO3- + H2O <--> HClO3 + OH-

In other circumstances, water accepts a proton from an acid and becomes hydronium (H3O+). The bond formed between the lone pair on the oxygen and the additional proton is called a coordinate covalent bond. Since water is accepting a proton, it is acting as a base.

HIO3 + H2O <--> IO3- + H3O+

Water is not the only substance that can be an acid or a base. Any substances that can act as either is called amphiprotic.

Answer 2

According to the Arrhenius Acid-Base theory, the answer is yes and no. If you rearrange the formula to look like HOH, you can see that it contains a hydrogen (indicating an acid), but also contains a hydroxide OH- (indicating a base).

This makes sense because water is dead center on the pH scale, right between the acidic side and the basic side.

Since we cannot tell by just "looking" at it to determine if its an acid or base, it has to be determined by how it reacts with other acids and bases.

This brings us to the Brønsted-Lowry acid-base theory, which tells us that acids are proton (H+ = H3O+) donors and bases are proton acceptors.

Generally, water will act as an acid (proton donor) when it reacts with a substance that is less acidic than the water. Conversely, water will act as a base when it reacts with a substance that is more acidic than water.

ExamplesHCl + H2O → H3O+ + Cl-

Hydrochloric acid is a strong acid and will ionize completely in water. It is more acidic than water, so the water acts as a base and accepts a proton. Note that the hydronium ion (H3O+) can also be written as a proton (H+).

NaOH + HOH → Na+ + OH-

Sodium hydroxide is a strong base and will ionize completely in water. It is less acidic than water, so the water acts as an acid and donates a proton to form a hydroxide.

Water is naturally neutral. Other things added to water may change it towards an acid or a base. Think of acid rain, or a poison water hole in the desert- acid and base.

Answer 3

Water can act as both an acid and a base through the process of autodissociation, where it can donate a proton (H+) to act as an acid or accept a proton to act as a base. In the presence of another acid, water can act as a base by accepting a proton. In the presence of a base, water can act as an acid by donating a proton.

Answer 4

Can what act as an acid or a base?

Answer 5

Water can both give away a proton to a base and become a hydroxide ion or accept a proton from an acid to become a hydronium ion.