Identifying Acid-Base Reactions (College Board AP Chemistry)

• Acid-Base reactions involves the transfer of one or more protons between chemical species
• Acids are species that donate protons
• Bases are species that accept protons
  • In the example below, HCl acts as an acid because it donates one proton to H₂O which acts as a base
  • Since HCl is just able to transfer one proton, it is a monoprotic acid

 HCl (aq) + H₂O (l) → H₃O⁺ (aq) + Cl^– (aq)

• There are acids that have the capability of donating more than one proton

• • Acids that are able to transfer two protons, are diprotic acids

H₂SO₄ (aq) + 2H₂O (l) → 2H₃O⁺ (aq) + SO₄^2– (aq) 

• • Acids that are able to transfer three protons, are triprotic acids

 H₃PO₄ (aq) + 3H₂O (l) → 3H₃O⁺ (aq) + PO₄^3– (aq)

Neutralization

• One of the most common acid-base reactions is neutralization
• Neutralization occurs when an acid reacts with a base/alkali to produce salt and water
  • The salt produced in the neutralization is formed from the cation of the base and the anion from the acid
  • Therefore the name of the salt can be predicted from the acid and base that have reacted
  • The cation and the anion the produce the salt are spectator ions

Acid reacted and salt produced

Acid Reacted	Salt produced
Hydrochloric acid	Chloride
Nitric Acid	Nitrate
Sulfuric acid	Sulfate

 

Diagram showing an acid-base neutralization

Neutralization reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) and their respective ionic equations to produce water (H₂O) and sodium chloride (NaCl)

Neutralization with gas formation

• The reaction of an acid and a metal carbonate or a metal hydrogen carbonate is also a neutralization reaction
• The products in both case are salt, water and carbon dioxide
  • Carbon dioxide is the product in gas state
• Examples for both cases are shown below:

acid + metal carbonate → salt + water + carbon dioxide

2HNO₃ (aq) + CuCO₃ (s) → Cu(NO₃)₂ (aq) + H₂O (l) + CO₂ (g)

acid + metal hydrogen carbonate → salt + water + carbon dioxide

HCl (aq) + NaHCO₃ (s) → NaCl (aq) + H₂O (l) + CO₂ (g)