Definition types reactions and examples of di and polybasic acids and bases
Acids are any substance which changes the colour of blue litmus paper to red, have sour taste inside the water, reacts with metals to form hydrogen ions (for example iron), reacts with bases to form salts and acts as a catalyst with specific reactions. Examples include – sulphuric acid, nitric acid, hydrochloric acid (mineral acid) and carbonic acid, sulphonic acid (organic acid) etc.
Polybasic Acids
Polybasic acids are those acids which are capable of yielding more than one hydronium per molecule. These may be called dibasic, tribasic etc. according to the number of hydrogens they can replace. Some examples of polybasic acids are sulphuric acid and phosphorus acid.
The ionization of a typical polybasic acid is written below:
\[H_{2} X(aq) \leftrightarrow H^{+} (aq) + HX^{-} (aq)\]
\[HX^{-} (aq) \leftrightarrow H^{+} (aq) + X_{2}^{-} (aq)\]
What are Polybasic Acids?
Generally, inorganic acids, when combined with base loose one atom of acid to get united with one atom oxide, therefore termed to be monoxide. However, some acids are already present as pyrophosphoric, who have the power to combine with a base, & then are termed as basic. Some examples of these types of acids are found among vegetables and the animal kingdoms.
Polybasic acids are also known as polyprotic acids. Ionization process takes place in a stepwise manner; within each step, one proton is released, the constant which is used to denote each step of the ionization process. The magnitude of the ionizing protons gets smaller and smaller with each step with the release of frequent protons subsequently.
What is Ionization?
Ionization is a process of losing or gaining molecules by an atom to form a charged ion. Ionization can be a result of the loss of electronic molecules after colliding with subatomic molecules and ions or interaction through electromagnetic radiation. Radiation energy knocks electrons from atoms, thereby agonizing them. This process is called ionizing radiation.
X + energy → X+ + e-
where x is any atom (to be ionized), x+ is any atom (with electron removed), and x- is any atom with (the removed electron).
The basicity of an acid depends on the number of hydrogen atoms it can replace in its molecule. If an acid can replace one atom of hydrogen ions, it is called a monobasic with the basicity of 1. Similarly, the acids which can replace two or three numbers of hydrogen ions are called as dibasic or tribasic with the basicity of 2 and 3 respectively. Some examples of acids with their basicities are given below.
Basicity of Acid
Basicity of Acetic Acid
Ethanoic acids contain four hydrogen atoms, with one of those atoms having direct contact with the oxygen atom, thus forming COOH- carboxyl group at the end of the carbon chains. The remaining of the hydrogen atoms would instinctively render the carbon chain unstable and is thus dramatically unfavourable.
CH3COOH (aq)+OH− (aq) → CH3COO− (aq) + H−O−H (l)
Acetic acid is an organic acid. It is a carboxylic acid which undergoes dissociation as follows:
CH3COOH → CH3COO- + H+
The basicity of Acetic acid is always one because the covalent bond between Carbon and Hydrogen is very strong. For the dissociation to properly occur, the solvent cannot provide sufficient energy. This results in the production of only 1 Hydrogen ion, and this is the reason the basicity is 1.
FAQs on Di Polybasic Acid and Base in Chemistry
1. What is a dibasic acid in chemistry?
A dibasic acid is an acid that can donate two ionizable hydrogen ions (H+) per molecule in aqueous solution.
- It contains two replaceable hydrogen atoms.
- It undergoes ionization in two steps.
- Example: H2SO4 and H2CO3.
- Stepwise ionization of sulfuric acid:
H2SO4(aq) → H+(aq) + HSO4-(aq)
HSO4-(aq) ⇌ H+(aq) + SO42-(aq)
2. What is a polybasic acid?
A polybasic acid is an acid that can donate more than one proton (H+) per molecule during ionization.
- They ionize in multiple steps.
- Each step has its own acid dissociation constant (Ka).
- Examples: H2SO4 (dibasic), H3PO4 (tribasic).
3. What is the difference between monobasic, dibasic, and tribasic acids?
The difference between monobasic, dibasic, and tribasic acids lies in the number of replaceable hydrogen ions (H+) they can donate.
- Monobasic acid: Donates 1 H+ (e.g., HCl).
- Dibasic acid: Donates 2 H+ (e.g., H2SO4).
- Tribasic acid: Donates 3 H+ (e.g., H3PO4).
4. What is a polybasic base?
A polybasic base is a base that can furnish more than one hydroxide ion (OH-) per molecule in aqueous solution.
- It contains more than one replaceable OH group.
- Example: Ca(OH)2, Ba(OH)2.
- Ionization of calcium hydroxide:
Ca(OH)2(aq) → Ca2+(aq) + 2OH-(aq)
5. How do you identify a dibasic acid from its chemical formula?
A dibasic acid is identified by the presence of two ionizable hydrogen atoms in its formula.
- Check if the formula starts with H2 (e.g., H2SO4).
- Ensure both hydrogens are replaceable (not part of water of crystallization).
- Confirm stepwise ionization produces two H+ ions.
6. Can you give an example of a tribasic (triprotic) acid with ionization steps?
A common example of a tribasic acid is phosphoric acid, H3PO4, which donates three protons stepwise.
- H3PO4(aq) ⇌ H+(aq) + H2PO4-(aq)
- H2PO4-(aq) ⇌ H+(aq) + HPO42-(aq)
- HPO42-(aq) ⇌ H+(aq) + PO43-(aq)
7. Why do polybasic acids ionize in steps?
Polybasic acids ionize in steps because each successive proton removal becomes energetically less favorable.
- The first proton is removed most easily.
- After losing one H+, the remaining ion becomes negatively charged.
- This negative charge makes removal of the next proton more difficult.
8. How do you calculate the normality of a dibasic acid?
The normality (N) of a dibasic acid is calculated as N = M × basicity, where M is molarity and basicity is 2.
- For a 0.5 M H2SO4 solution:
- N = 0.5 × 2 = 1.0 N
9. What is the difference between polybasic acid and polyprotic acid?
The terms polybasic acid and polyprotic acid are often used interchangeably to describe acids that donate more than one proton.
- Polybasic refers to the number of replaceable hydrogen atoms.
- Polyprotic emphasizes multiple proton donation steps.
- Example: H2SO4 is both dibasic and diprotic.
10. How does a dibasic acid react with a base?
A dibasic acid reacts with a base in a neutralization reaction to form salt and water, requiring two moles of a monobasic base for complete neutralization.
- Example with sodium hydroxide:
- H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l)
