Question

For \(\mathrm{H}_{3} \mathrm{PO}_{3}\) and \(\mathrm{H}_{3} \mathrm{PO}_{4}\) the correct choice is (a) \(\mathrm{H}_{3} \mathrm{PO}_{3}\) is dibasic and reducing (b) \(\mathrm{H}_{3} \mathrm{PO}_{3}\) is dibasic and non-reducing (c) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) is tribasic and reducing (d) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) is tribasic and non-reducing

Short answer

(a) H_{3}PO_{3} is dibasic and reducing.

Step-by-step solution

Understanding the Acidity

For an acid like phosphorous acid ( H_{3}PO_{3} ) or phosphoric acid ( H_{3}PO_{4} ), the basicity refers to the number of ionizable hydrogen atoms that can donate as protons (H+ ions). In H_{3}PO_{3} , only two of the hydrogen atoms are ionizable because the structure has one hydrogen atom directly bonded to phosphorous. In H_{3}PO_{4} , all three hydrogen atoms are on hydroxyl groups, which makes all of them ionizable.

Determining Basicity

H_{3}PO_{3} is dibasic because it can donate two hydrogen ions (H+), as two oxygens have hydrogen atoms attached, different from one bonded directly to phosphorus. H_{3}PO_{4} is tribasic because it can donate three hydrogen ions, each linked to the oxygen in hydroxyl groups.

Determining Reducing Ability

To determine if the acids are reducing, we examine the oxidation states and the structure. H_{3}PO_{3} can act as a reducing agent because it contains an atom of hydrogen bonded directly to phosphorus. This bond can be used to reduce other species. H_{3}PO_{4} cannot act similarly because all hydrogen is bound to oxygen.

Aligning Choices with Properties

Based on the two properties analyzed, H_{3}PO_{3} satisfies the property of being dibasic and also a reducing agent. H_{3}PO_{4} is tribasic and does not have reducing properties.

Final Choice

Given the evaluation of properties: H_{3}PO_{3} is dibasic and reducing (option (a)); H_{3}PO_{4} is tribasic and non-reducing (matches option (d)). Thus, options that describe the acids correctly are (a) and (d), but given the task to pick the property description of H_{3}PO_{3} , choice (a) is correct.

Key concepts

Ionization of acids

When it comes to acids, ionization refers to the process where an acid donates hydrogen ions, also known as protons. This happens because the hydrogen atoms in an acid are often bonded in such a way that they can easily detach. Specifically, for a molecule like \( \mathrm{H_{3}PO_{3}} \), ionization can occur with its hydrogen atoms, but only the ones which are loosely attached to its oxygen atoms are capable of doing so.

In contrast, the acid \( \mathrm{H_{3}PO_{4}} \), which is phosphoric acid, has all its hydrogen atoms attached to oxygens in hydroxyl groups. This structure allows all three hydrogens to be ionizable, making it tribasic.

• \( \mathrm{H_{3}PO_{3}} \) - Ionizes two hydrogens, thus is dibasic.
• \( \mathrm{H_{3}PO_{4}} \) - Ionizes all three hydrogens, making it tribasic.

Reducing agents

Reducing agents play a crucial role in chemical reactions, especially in redox reactions. They are substances that donate electrons to another substance, often reducing the oxidation state of the recipient. In simpler terms, a good reducing agent gives away electrons easily.

In phosphorous acid \( \mathrm{H_{3}PO_{3}} \), the presence of hydrogen bonded directly to phosphorus is crucial. This unique bond allows \( \mathrm{H_{3}PO_{3}} \) to act as a reducing agent because it means \( \mathrm{H_{3}PO_{3}} \) can donate electrons more easily.

Conversely, in \( \mathrm{H_{3}PO_{4}} \), no such hydrogen-phosphorus bond is present, so it does not act as a reducing agent.

• \( \mathrm{H_{3}PO_{3}} \) - Can act as a reducing agent.
• \( \mathrm{H_{3}PO_{4}} \) - Does not act as a reducing agent.

Phosphorous acid properties

Phosphorous acid, with formula \( \mathrm{H_{3}PO_{3}} \), has some intriguing chemical properties.

The most notable property includes its basicity, which is dibasic because its molecular structure allows two hydrogen atoms to be ionizable. This makes it capable of dissociating two protons during a chemical reaction.

Moreover, its ability to act as a reducing agent comes from its structural peculiarities. The direct hydrogen-phosphorus bond in its structure allows it to easily donate electrons.

This makes phosphorous acid a useful compound in reactions where reduction is needed.

• Basicity: Dibasic.
• Reducing ability: Can reduce other compounds due to its hydrogen-phosphorus bond.

Phosphoric acid properties

Phosphoric acid, or \( \mathrm{H_{3}PO_{4}} \), is well known for being tribasic, meaning it can donate three protons (hydrogen ions).

This characteristic arises because all three hydrogen atoms are connected via hydroxyl groups, which are very prone to ionization.

However, unlike some acids, it does not have reducing properties due to its structural formation where its hydrogen atoms are not directly bonded to phosphorous.

• Basicity: Tribasic, can release three hydrogen ions.
• Reducing ability: Lacks reducing properties, as no direct hydrogen-phosphorus bonds are present.