Acids and Bases: An Introduction
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Is water an acid or base?

Use the following equations to complete the following statements:

In this reaction, H2O is a proton

 .

Therefore, H2O is

.

In this reaction, H2O is a proton

 .

Therefore, H2O is

.

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In the first reaction, the acidic nature of hydrogen fluoride can be described by saying it donates a hydrogen ion to the water. This means the water is accepting the hydrogen ion, which classifies it as a base using the Brønsted concept.

In the second reaction, the basic nature of ammonia can be described by saying it accepts a hydrogen ion from the water. This means the water is donating the hydrogen ion, which classifies it as an acid using the Brønsted concept.

In the first reaction, the acidic nature of hydrogen fluoride can be described by saying it donates a hydrogen ion to the water. This means the water is accepting the hydrogen ion, which classifies it as a base using the Brønsted concept.

In the second reaction, the basic nature of ammonia can be described by saying it accepts a hydrogen ion from the water. This means the water is donating the hydrogen ion, which classifies it as an acid using the Brønsted concept.

Good! As these two reactions show, water can act as an acid or a base; molecules (or ions) that can do this are called amphiprotic. When an amphiprotic molecule (or ion) reacts with an acid, it acts as a base. When an amphiprotic molecule (or ion) reacts with a base, it acts as an acid.