What is a triprotic acid

Polyprotic Acids and Bases

what is a triprotic acid

Polyprotic Acids

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The acid equilibrium problems discussed so far have focused on a family of compounds known as monoprotic acids. There is usually a large difference in the ease with which these acids lose the first and second or second and third protons. When sulfuric acid is classified as a strong acid, students often assume that it loses both of its protons when it reacts with water. That isn't a legitimate assumption. Sulfuric acid is a strong acid because K a for the loss of the first proton is much larger than 1. We therefore assume that essentially all the H 2 SO 4 molecules in an aqueous solution lose the first proton to form the HSO 4 - , or hydrogen sulfate, ion. The table below gives values of K a for some common polyprotic acids.

The name "polyprotic" literally means many protons. Therefore, in this section we will be observing some specific acids and bases which either lose or accept more than one proton. Then, we will be talking about the equations used in finding the degree of dissociation. Finally, with given examples, we will be able to approach problems dealing with polyprotic acids and bases. Polyprotic acids are specific acids that are capable of losing more than a single proton per molecule in acid-base reactions.

Acids and bases can be classified as either monoprotic or polyprotic. This article will focus on polyprotic acids and bases, including reactions between polyprotic acids and bases, and how properties of polyprotic acids and bases affect pH. Polyprotic acids will release multiple hydrogen ions. As a result, every molecule of all polyprotic acids must have at least two hydrogen ions. The stability of the structure of the molecule sometimes plays a role in how many hydrogen ions a polyprotic acid molecule will release.

Diprotic and polyprotic acids contain multiple acidic protons that dissociate in distinct, sequential steps. As their name suggests, polyprotic acids contain more than one acidic proton. Two common examples are carbonic acid H 2 CO 3 , which has two acidic protons and is therefore a diprotic acid and phosphoric acid H 3 PO 4 , which has three acidic protons and is therefore a triprotic acid. Diprotic and polyprotic acids show unique profiles in titration experiments, where a pH versus titrant volume curve clearly shows two equivalence points for the acid; this is because the two ionizing hydrogens do not dissociate from the acid at the same time. With any polyprotic acid, the first amd most strongly acidic proton dissociates completely before the second-most acidic proton even begins to dissociate. Titration curve of carbonic acid : The titration curve of a polyprotic acid has multiple equivalence points, one for each proton.



Polyprotic Acids & Bases

This idea of proton donor and proton acceptor is important in understanding monoprotic and polyprotic acids and bases because monoprotic corresponds to the transfer of one proton and polyprotic refers to the transfer of more than one proton. Therefore, a monoprotic acid is an acid that can donate only one proton, while polyprotic acid can donate more than one proton. Similarly, a mon oprotic base can only accept one proton, while a polyprotic base can accept more than one proton.

Polyprotic Acid Definition in Chemistry

Examples of triprotic acid in the following topics: Polyprotic Acid Titrations Certain types of polyprotic acids have more specific names, such as diprotic acid two potential protons to donate and triprotic acid three potential protons to donate. Likewise, a triprotic system can be envisioned. An example of a triprotic acid is orthophosphoric acid H3PO4 , usually just called phosphoric acid. Another example of a triprotic acid is citric acid , which can successively lose three protons to finally form the citrate ion. Triprotic acids can make three distinct proton donations, each with a unique Ka.

We can classify acids by the number of protons per molecule that they can give up in a reaction. Their reactions with water are:. Even though it contains four hydrogen atoms, acetic acid, CH 3 CO 2 H, is also monoprotic because only the hydrogen atom from the carboxyl group COOH reacts with bases:. Diprotic acids contain two ionizable hydrogen atoms per molecule; ionization of such acids occurs in two steps. The first ionization always takes place to a greater extent than the second ionization.

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