Lesson: Chapter - 6

Acid–Base Reactions: Neutralization Reactions

When a strong acid and a strong base solution are mixed, a neutralization reaction occurs, and the products do not have characteristics of either acids or bases. Instead, a neutral salt and water are formed. Look at the reaction below:

HCl_(aq) + NaOH_(aq) ? H₂O_(l) + NaCl_(aq)

The anion from the acid (Cl^–) reacts with the cation from the base (Na⁺) to give a salt, and a salt is defined as any compound formed whose anion came from an acid and whose cation came from a base.

When a strong acid and a weak base are mixed, the resulting salt will be acidic; likewise, if a strong base and a weak acid are mixed, the resulting salt will be basic. If on the SAT II Chemistry test you are asked to determine if a salt formed in a particular reaction is neutral, acidic, or basic, first ask yourself, Which acid reacted with which base to form this salt? Next ask yourself, Was the acid strong or weak? and then, Was the base strong or weak? Consider K₂CO₃. K₂CO₃ is formed when the base, potassium hydroxide (which is strong since potassium is a 1A metal), reacts with the acid, H₂CO₃ (which is weak since it isn’t one of our six strong acids). Since this is a combination of a strong base and a weak acid, the salt formed will be basic.

The good news is that for the SAT II Chemistry exam, you needn’t worry about weak-weak combinations. Now try some problems on your own.

Example

Classify each of the salts listed below as acidic, basic, or neutral.

1. Fe(NO₃)₃
2. MgSO₄
3. Ni(ClO₄)₂

Explanation

1. Fe(NO₃)₃—This salt was formed from the reaction of a weak base, iron (III) hydroxide, with a strong acid, nitric acid. This means that the salt will be acidic.
2. MgSO₄—This salt was formed from the reaction of a strong base, magnesium hydroxide, with strong acid, sulfuric acid. This reaction results in a neutral salt.
3. Ni(ClO₄)₂—This salt was formed from the reaction of a weak base, nickel (II) hydroxide, with a strong acid, perchloric acid. This is an acidic salt.

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