Salt formation reaction: Salt formation reaction is a chemical process in which a cation (positively charged ion) and an anion (negatively charged ion) combine to produce a salt — an electrically neutral ionic compound — usually as a result of an acid–base reaction, a metal–acid reaction, or an ion-exchange process, occurring in either aqueous or non-aqueous solvents.
Salt Formation Reactions — Compact Table with Overall Reactions
| Salt Name | Formula | Solvent | Reaction Equation |
|---|---|---|---|
| Sodium chloride | NaCl | Water (aqueous) | \( \mathrm{HCl_{(aq)} + NaOH_{(aq)} \to NaCl_{(aq)} + H_2O_{(l)}} \) |
| Sodium ureide | Na(NH2CONH) | Liquid ammonia (liq. NH3) | \( \mathrm{NaNH_2 + NH_2CONH_2 \xrightarrow{liq.\ NH_3} Na(NH_2CONH) + NH_3} \) |
| Phosphonium tetrachloroborate | PH4[BCl4] | Liquid HCl (liq. HCl) |
\( \mathrm{PH_3 + HCl_{(liq)} \to PH_4^+ + Cl^-; \quad BCl_3 + Cl^- \to [BCl_4]^-} \) Overall: \( \mathrm{PH_3 + HCl_{(liq)} + BCl_3 \to PH_4[BCl_4]} \) |
| Nitrosonium tetrachloroborate | NO[BCl4] | Liquid HCl (liq. HCl) |
\( \mathrm{NOCl \xrightarrow{liq.\ HCl} NO^+ + Cl^-; \quad BCl_3 + Cl^- \to [BCl_4]^-} \) Overall: \( \mathrm{NOCl + BCl_3 \xrightarrow{liq.\ HCl} NO[BCl_4]} \) |
Important Notes on Salt Formation in Different Solvents
- Sodium ureide (Na(NH₂CONH)) cannot be isolated in aqueous medium because it undergoes hydrolysis in water, regenerating NaOH and urea. Since NaOH is a strong base, it cannot accept a proton from urea, preventing stable salt formation in water.
- Phosphonium salts like PH₄[BCl₄] are unstable in water. The phosphonium ion (PH₄⁺) donates a proton to water, producing hydronium ion (H₃O⁺) and phosphine gas (PH₃), thus decomposing the salt. These salts are stable and can be prepared only in liquid HCl, where PH₄⁺ exists without proton transfer.
- Similarly, nitrosonium salts such as NO[BCl₄] do not form in aqueous solutions because NO⁺ reacts with water to form nitrous acid (HONO). In liquid HCl, however, NO⁺ behaves as a weak base and forms the stable salt NO[BCl₄].