Neutralization Reactions
Quick Notes
- Neutralization reaction = acid + base → salt + water (and sometimes CO₂)
- Metal oxides and hydroxides react with acids to form salt + water
- Carbonates and hydrogencarbonates react with acids to form salt + water + carbon dioxide
- Ammonia (NH₃) and amines act as bases in neutralization
- Organic acids (like ethanoic acid) can also participate in neutralization reactions
- Identify parent acid (e.g. HCl forms chloride salts) and base (e.g. NaOH forms sodium salts) to determine the name of the salt
Full Notes
What Are Neutralization Reactions?
Neutralization reactions occur when an acid reacts with a base, producing a salt and water.In some cases, carbon dioxide is also produced.
These reactions are fundamental in acid–base chemistry and you should get comfortable with them.
Common Neutralization Reactions
Acid + Metal Oxide → Salt + Water
Example: H₂SO₄ + CuO → CuSO₄ + H₂O
Acid + Metal Hydroxide → Salt + Water
Example: HCl + NaOH → NaCl + H₂O
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
Example: 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
Acid + Metal Hydrogencarbonate → Salt + Water + Carbon Dioxide
Example: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂
Common Bases
Neutralization can involve a range of bases (all act as bases by accepting H⁺ ions):
- Metal oxides (e.g. CuO)
- Metal hydroxides (e.g. NaOH, Ca(OH)₂)
- Ammonia (NH₃) and amines
- Soluble carbonates (e.g. Na₂CO₃)
- Hydrogencarbonates (e.g. NaHCO₃)
Organic Acids and Neutralization
Organic acids like ethanoic acid (CH₃COOH) also undergo neutralization with the same types of bases as above.
Example Ethanoic Acid + Ammonia
CH₃COOH + NH₃ → CH₃COONH₄
Identifying the Parent Acid and Base
To name the salt formed in a neautralization reaction:
- The metal/positive ion comes from the base
- The negative ion (anion) comes from the acid
Example Common Salts
- HCl (acid) + NaOH (base) → NaCl
Parent acid: HCl → chloride
Parent base: NaOH → sodium - H₂SO₄ + CaCO₃ → CaSO₄
Sulfate from sulfuric acid
Calcium from carbonate base
Summary
- Neutralization reactions produce salt and water, sometimes CO₂.
- Different bases can neutralize acids, including oxides, hydroxides, and ammonia.
- Organic acids also undergo neutralization.
- Salts are named from the parent acid and base.
- Neutralization is exothermic due to bond enthalpies.
- Acid–metal reactions that release H₂ are redox processes.
Linked Course Questions
How can the salts formed in neutralization reactions be separated?
Salts formed in neutralization reactions (acid + base) can be separated using evaporation or crystallization:
- For soluble salts, gently evaporate the water from the solution until crystals start to form, then allow it to cool so the salt crystallizes. Filter and dry the crystals.
- For insoluble salts, use filtration if the salt precipitates out. Wash the solid with water and dry it.
Neutralization reactions are exothermic. How can this be explained in terms of bond enthalpies?
Neutralization reactions release heat because more energy is released making new bonds than is required to break existing ones.
In a typical neutralization:
- An acid donates a proton (H⁺)
- A base donates a hydroxide ion (OH⁻)
- These combine to form water (H₂O)
Forming the O–H bonds in water releases a large amount of energy. Breaking the H⁺ and OH⁻ from the acid and base requires less energy than is released when they bond. The net energy change is negative (exothermic), which is why neutralization reactions give off heat.
How could we classify the reaction that occurs when hydrogen gas is released from the reaction between an acid and a metal?
This reaction can be classified as a redox reaction:
- The metal is oxidized, losing electrons to form metal ions.
- The hydrogen ions (H⁺) from the acid are reduced, gaining electrons to form hydrogen gas (H₂).
Example Mg + 2HCl → MgCl₂ + H₂
- Mg → Mg²⁺ + 2e⁻ (oxidation)
- 2H⁺ + 2e⁻ → H₂ (reduction)
So the release of hydrogen gas signals a redox process involving electron transfer.