Look at the reaction below: H2SO4(aq) + Ca(OH)2(aq) → CaSO4(aq) + 2H2O(l) Which substance is the base in the reaction? 2H2O(l) H2SO4(aq) CaSO4(aq) Ca(OH)2(aq)
The Correct Answer and Explanation is:
Correct Answer: Ca(OH)₂(aq)
In the given chemical reaction:
H₂SO₄(aq) + Ca(OH)₂(aq) → CaSO₄(aq) + 2H₂O(l)
The substance that acts as the base is Ca(OH)₂(aq), which is calcium hydroxide.
Explanation:
In acid-base chemistry, substances are identified as acids or bases based on their ability to donate or accept protons (H⁺ ions). According to the Brønsted-Lowry theory:
- An acid is a substance that donates protons.
- A base is a substance that accepts protons.
H₂SO₄, or sulfuric acid, is a strong acid. It donates hydrogen ions (H⁺) when dissolved in water. Specifically, H₂SO₄ donates two H⁺ ions because it is a diprotic acid.
Ca(OH)₂, or calcium hydroxide, is a strong base. It releases hydroxide ions (OH⁻) when dissolved in water. These OH⁻ ions can combine with H⁺ ions from the acid to form water (H₂O).
In this neutralization reaction:
- H₂SO₄ provides H⁺ ions.
- Ca(OH)₂ provides OH⁻ ions.
- The H⁺ and OH⁻ combine to form water (2H₂O).
- The remaining ions, Ca²⁺ from calcium hydroxide and SO₄²⁻ from sulfuric acid, form the salt CaSO₄, or calcium sulfate.
Therefore, Ca(OH)₂ is the base because it provides hydroxide ions that react with hydrogen ions from the acid. The products of this neutralization reaction are a salt (CaSO₄) and water. This is a typical reaction between a strong acid and a strong base.
In conclusion, calcium hydroxide acts as the base in this reaction due to its role in accepting protons and neutralizing the acid.
