How do monobasic and dibasic acids differ?

What is a dibasic acid?

In acid-base chemistry, a dibasic acid can provide two positively charged hydrogen ions or protons when it reacts with a base. A modern term for this type of acid is a diprotic acid. An acid and a base usually react to form a salt and water. The water results from the positively charged hydrogen ion of the acid, which reacts with the negatively charged hydroxide ion of the base: H + + OH - → H 2 O. In a dibasic acid molecule, two hydrogen atoms are available for reaction, i.e. two types of salt can be formed, one of which is an acid salt containing a hydrogen atom.

An acid that can only provide one proton is known as a monoprote or monobasic acid. Examples are hydrochloric acid (HCl) and nitric acid (HNO 3 ). There are also polyprotic acids that can deliver more than two protons - for example phosphoric acid H. 3 PO 4 that is triprotic. There is no connection between the number of hydrogen atoms in the acid molecule and the strength of the acid - this depends on the extent to which the hydrogen in the molecule splits off into hydrogen ions in solution. An acid with one hydrogen atom that easily splits off is stronger than one with two hydrogen atoms that doesn't. For example, hydrochloric acid (HCl) - a monobasic acid - is a much stronger acid than the dibasic carbonic acid (H. 2 CO 3 ).

The terms monobasic and dibasic are rarely used for acids these days, but older chemistry textbooks may use them. Acids today are usually described as monoprotic, diprotic, triprotic, etc. The term dibasic can still be seen in connection with bases, for example calcium hydroxide (Ca (OH) 2 ) can be described as dibasic because it has two hydroxide groups that can combine with an H + ion from an acid to form water.

Sulfuric acid, one of the most famous and widely used acids, is a good example of a dibasic acid. It can form two types of salts known as sulfates and hydrogen sulfates, sometimes called bisulfates. Carbonic acid is another common dibasic acid that can similarly form carbonates and bicarbonates. The latter are often referred to as bicarbonates. Sodium bicarbonate, or baking soda, is the best known of these. These acidic salts can be acidic as in sodium hydrogen sulfate or basic as in sodium hydrogen carbonate; The term simply means that the salt contains a hydrogen atom that is derived from an acid.

Not all hydrogen atoms in an acid molecule are necessarily available to form H + ions and to react with bases. It is therefore not possible to tell by simply counting the hydrogen atoms in the molecule whether an acid is monoprotic, diprotic or polyprotic. This is especially true for organic acids, which can have relatively complex structures in which hydrogen occurs in other roles. An example is tartaric acid (C. 4 H 6 O 6 ). The molecule consists of six hydrogen atoms, which are structured in such a way that only two of them can break down into hydrogen ions in solution. it is therefore a dibasic acid.