What is the primary factor determining the thermal stability of Group 1 and Group 2 carbonates?

The primary factor is the polarizing power of the cation. Smaller, highly charged cations (like $Li^+$ or $Be^{2+}$) have a greater polarizing power. This means they can distort the electron cloud of the large carbonate anion ($CO_3^{2-}$), weakening the C-O bonds and making it easier for the anion to decompose into $CO_2$ and $O^{2-}$. As you go down a group, the cation size increases, its polarizing power decreases, and thus the thermal stability of the carbonate salt increases. Lattice energy also plays a role, but polarizing power is often the dominant factor in decomposition trends.

Why are most nitrates soluble in water?

The high solubility of nitrates is attributed to the relatively weak electrostatic interactions between the nitrate ion ($NO_3^-$) and most cations, combined with the high hydration energy of the ions. The nitrate ion is a large, planar anion with delocalized charge, which makes it less effective at forming strong lattice structures with cations compared to smaller, more localized charge anions. Additionally, the hydration of both the cation and the nitrate ion provides sufficient energy to overcome the lattice energy, leading to dissolution.

How can I predict if a salt of an oxoacid will form an acidic, basic, or neutral solution in water?

You need to consider the strengths of the parent acid and base from which the salt is formed. If the salt is from a strong acid and strong base (e.g., $Na_2SO_4$), the solution will be neutral. If it's from a strong acid and weak base (e.g., $NH_4Cl$), the solution will be acidic due to cation hydrolysis. If it's from a weak acid and strong base (e.g., $Na_2CO_3$), the solution will be basic due to anion hydrolysis. If both are weak (e.g., $CH_3COONH_4$), the pH depends on the relative strengths of the acid and base.

What are common decomposition products of metal nitrates upon heating?

The decomposition products depend on the metal. Alkali metal nitrates (except $LiNO_3$) typically decompose to the corresponding metal nitrite and oxygen, e.g., $2NaNO_3 \rightarrow 2NaNO_2 + O_2$. However, nitrates of lithium, alkaline earth metals, and many transition metals decompose to the metal oxide, nitrogen dioxide ($NO_2$), and oxygen, e.g., $2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2$. Ammonium nitrate decomposes to dinitrogen monoxide ($N_2O$) and water, $NH_4NO_3 \rightarrow N_2O + 2H_2O$.

Can salts of oxoacids act as both oxidizing and reducing agents?

Yes, some salts of oxoacids can act as both, depending on the oxidation state of the central atom in the oxoanion. If the central atom is in an intermediate oxidation state, it can be further oxidized (acting as a reducing agent) or reduced (acting as an oxidizing agent). For example, the sulfite ion ($SO_3^{2-}$), with sulfur in the +4 oxidation state, can be oxidized to sulfate ($SO_4^{2-}$, sulfur +6) or reduced to sulfur (0) or sulfide (-2). Similarly, nitrites ($NO_2^-$) can be oxidized to nitrates ($NO_3^-$) or reduced to $NO$ or $N_2$.

Why is lithium carbonate less thermally stable than other alkali metal carbonates?

Lithium carbonate ($Li_2CO_3$) is an exception to the general trend of increasing thermal stability down Group 1. This is because the $Li^+$ ion is very small and has a high charge density (high polarizing power). This strong polarizing power distorts the electron cloud of the large carbonate ion ($CO_3^{2-}$), weakening the C-O bonds and making it easier for $Li_2CO_3$ to decompose at a lower temperature, similar to Group 2 carbonates. The other alkali metal cations are much larger and have lower polarizing power, leading to more stable carbonates.

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Salts of Oxoacids

Chemistry

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Version 1Updated 22 Mar 2026

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Salts of oxoacids are ionic compounds formed when the acidic hydrogen atoms of an oxoacid are replaced by metal cations or ammonium ions. An oxoacid is an acid that contains oxygen, and typically has at least one hydrogen atom bonded to an oxygen atom, which can dissociate to form a proton ( $H^+$ ) and an oxoanion. The oxoanion, which is the conjugate base of the oxoacid, contains a central atom bo…

Quick Summary

Salts of oxoacids are ionic compounds formed when the acidic hydrogen atoms of an oxoacid (an acid containing oxygen, like $H_2SO_4$ ) are replaced by metal or ammonium cations. The resulting anion, called an oxoanion (e.

g., $SO_4^{2-}$ ), contains a central atom bonded to oxygen. Key properties include solubility, thermal stability, and redox behavior. Most nitrates are soluble, while most carbonates and phosphates are insoluble (except for alkali metals and ammonium).

Thermal stability trends are crucial: for Group 1 and 2 carbonates and nitrates, stability generally increases down the group due to decreasing polarizing power of the cation. Salts with central atoms in high oxidation states (e.

g., nitrates, perchlorates) act as oxidizing agents, while those in lower oxidation states (e.g., sulfites, nitrites) act as reducing agents. Hydrolysis of these salts can lead to acidic, basic, or neutral solutions depending on the parent acid and base strengths.

These salts are vital in agriculture, construction, and various industries.

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Key Concepts

Thermal Stability Trends of Carbonates

The thermal stability of metal carbonates generally increases down a group in the periodic table. This is…

Solubility Rules for Common Oxoacid Salts

Understanding general solubility rules is crucial for predicting reactions and properties. Most nitrates…

Redox Behavior of Nitrates

The nitrate ion ( $NO_3^-$ ) contains nitrogen in its highest oxidation state (+5), making it a strong…

Oxoacids: — Acids with acidic H-O bonds (e.g.,

H_2SO_4

HNO_3

Salts: — Formed by replacing acidic H with cations (e.g.,

Na_2SO_4

CaCO_3

Solubility:

- Nitrates ( $NO_3^-$ ): All soluble. - Sulfates ( $SO_4^{2-}$ ): Mostly soluble; exceptions: $BaSO_4$ , $PbSO_4$ , $SrSO_4$ , $CaSO_4$ (sparingly). - Carbonates ( $CO_3^{2-}$ ), Phosphates ( $PO_4^{3-}$ ): Mostly insoluble; exceptions: Group 1 & $NH_4^+$ salts.

Thermal Stability:

- Group 1 & 2 Carbonates/Nitrates: Stability $\uparrow$ down group (due to $downarrow$ polarizing power of cation). - $Li_2CO_3$ : Exception, less stable than other Group 1, like Group 2. - Decomposition: $MCO_3 \rightarrow MO + CO_2$ ; $2MNO_3 \rightarrow 2MNO_2 + O_2$ (Group 1); $2M(NO_3)_2 \rightarrow 2MO + 4NO_2 + O_2$ (Group 2, heavy metals); $NH_4NO_3 \rightarrow N_2O + 2H_2O$ .

Redox:

- Oxidizing agents: Central atom in high O.S. (e.g., $NO_3^-$ , $ClO_4^-$ ). - Reducing agents: Central atom in intermediate O.S. (e.g., $SO_3^{2-}$ , $NO_2^-$ ).

Hydrolysis:

- Strong Acid + Strong Base: Neutral. - Strong Acid + Weak Base: Acidic. - Weak Acid + Strong Base: Basic.

Never Stop Calculating Problems: Nitrates Soluble, Sulfates Soluble (except Big People Sit Carefully - $Ba, Pb, Sr, Ca$ ), Carbonates & Phosphates Insoluble (except Always Always - Alkali Metals & Ammonium).

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