Identifying Acid-Base Reactions (College Board AP® Chemistry)

Identifying Acid-Base Reactions

• 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

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)