A reaction in which an acid and a base react to produce water and a salt is called a neutralization reaction. It is central to acid–base chemistry.
Basic Knowledge
A neutralization reaction is one in which H+ from an acid combines with OH- from a base to form water.H+ + OH- → H2O
At the same time, a salt is formed from the anion of the acid and the cation of the base.
Example: HCl + NaOH → NaCl + H2O
Example: H2SO4 + 2NaOH → Na2SO4 + 2H2O
Salts are classified into the following three types.
・Normal salt: Neither H from the acid nor OH from the base remains (NaCl, Na2SO4)
・Acid salt: H remains (NaHCO3, NaHSO4)
・Basic salt: OH remains (MgCl(OH))
※ “Acid salt” and “basic salt” are names for classifications and do not necessarily mean that their aqueous solutions are acidic or basic.
Neutralization reaction (A reaction that produces water and a salt from an acid and a base)
Salt (A compound formed from the anion of an acid and the cation of a base)
Normal salt (A salt in which neither H nor OH remains. NaCl, KNO3)
Acid salt (A salt in which H remains. NaHCO3, NaHSO4)
Basic salt (A salt in which OH remains. MgCl(OH))
Salt hydrolysis (A phenomenon in which a salt derived from a weak acid or weak base reacts with water and changes the solution's properties)
Further Exploration (Background and Significance)
The properties of a normal salt's aqueous solution are determined by the relative strengths of the original acid and base (hydrolysis).
・Strong acid + strong base → normal salt is neutral (NaCl solution is neutral)
・Strong acid + weak base → normal salt is acidic (NH4Cl solution is weakly acidic)
・Weak acid + strong base → normal salt is basic (CH3COONa solution is weakly basic)
・Weak acid + weak base → generally neutral
The quantitative relationship in a neutralization reaction is determined by “amount of substance of H+ from the acid = amount of substance of OH- from the base.” This will be discussed in detail in the next lesson on acid–base titration.
- Neutralization: H+ + OH- → H2O
- Anion of acid + cation of base → salt
- Normal salt, acid salt, and basic salt are classification rules
- NaCl is a normal salt and is neutral
- NaHCO3 is an acid salt, but its aqueous solution is basic
- Normal salt from strong acid + weak base → aqueous solution is acidic
- Normal salt from weak acid + strong base → aqueous solution is basic
Points of Caution (Common Confusions)
① “Acid salt” and “basic salt” are classification names and are different from the properties of their aqueous solutions. NaHCO3 is an acid salt, but its aqueous solution is basic. ② Neutralization is a reaction in which water is always formed. ③ When the basicity/acidity differs, adjust the coefficients to determine the neutralization point (for example, H2SO4 1 mol = NaOH 2 mol). ④ Salt has a broader meaning than table salt alone.
Practice
- Write the products in
H2SO4 + 2NaOH → ?. - Which is an acid salt among NaCl, NaHCO3, and MgCl(OH)?
- State whether an aqueous solution of CH3COONa is acidic, neutral, or basic, and explain why.