7.9: Acid-Base and Gas Evolution Reactions
- Page ID
- 289400
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- Identify when a reaction will evolve a gas.
Neutralization Reactions
Acids and bases react chemically with each other to form salts. A salt is a general chemical term for any ionic compound formed from an acid and a base. In reactions where the acid is a hydrogen-ion-containing compound and the base is a hydroxide-ion-containing compound, water is also a product. The general reaction is as follows:
acid + base → salt + water
The reaction of acid and base to make water and a salt is called neutralization. Like any chemical equation, a neutralization chemical equation must be properly balanced. For example, the neutralization reaction between sodium hydroxide and hydrochloric acid is as follows:
NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
with coefficients all understood to be one. The neutralization reaction between sodium hydroxide and sulfuric acid is as follows:
2 NaOH (aq) + H2SO4 (aq) → Na2SO4 (aq) + 2 H2O (l)
✅ Example \(\PageIndex{1}\): Neutralizing Nitric Acid
Nitric acid, HNO3 (aq), can be neutralized by calcium hydroxide, Ca(OH)2 (aq). Write a balanced chemical equation for the reaction between these two compounds and identify the salt that it produces.
Solution
Write the unbalanced equation. This is a double replacement reaction, so the cations and anions swap to create new products. Referring to the solubility rules, Ca(NO3)2 is soluble in water resulting in a phase label of (aq). Water, H2O, is a liquid at room temperature resulting in a phase label of (l).
Ca(OH)2 (aq) + HNO3 (aq) → Ca(NO3)2 (aq) + H2O (l)
At this point, the equation may be balanced by placing a coefficient of "2" in front of HNO3 (aq) and H2O (l).
Ca(OH)2 (aq) + 2 HNO3 (aq) → Ca(NO3)2 (aq) + 2 H2O (l)
The salt formed is calcium nitrate, Ca(NO3)2 (aq).
✏️ Exercise \(\PageIndex{1}\)
Hydrobromic acid, HBr (aq), may be neutralized with potassium hydroxide, KOH (aq). Write a balanced chemical equation for the reaction between these two compounds and identify the salt that it produces.
- Answer
- KOH (aq) + HBr (aq) → KBr (aq) + H2O (l)
The salt is potassium bromide, KBr (aq).
Gas Evolving Reactions
Figure \(\PageIndex{1}\) shows an apparatus that may be used for collecting gases in the laboratory.
A gas evolution reaction is a chemical process that produces a gas, such as hydrogen or carbon dioxide. In the following examples, an acid reacts with a carbonate, producing salt, carbon dioxide, and water, respectively. For example, nitric acid reacts with sodium carbonate to form sodium nitrate, carbon dioxide, and water (Table \(\PageIndex{1}\)):
2 HNO3 (aq) + Na2CO3 (aq) → 2 NaNO3 (aq) + CO2 (g) + H2O (l)
Hydrochloric acid reacts with calcium carbonate to form calcium chloride, carbon dioxide, and water:
2 HCl (aq) + CaCO3 (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
The oxidation of metals by strong acids is another common example of a gas evolution reaction. This reaction will yield a metal salt and hydrogen gas.
2 HCl (aq) + Zn (s) → ZnCl2 (aq) + H2 (g)
Here, hydrochloric acid oxidizes zinc to produce an aqueous metal salt and hydrogen gas bubbles.
This page is shared under a CC BY 4.0 and CK-12 licenses and was authored, remixed, and/or curated by Boundless (www.boundless.com), Wikipedia, Paul Flowers (University of North Carolina - Pembroke), Klaus Theopold (University of Delaware) and Richard Langley (Stephen F. Austin State University) with contributing authors, Marisa Alviar-Agnew & Henry Agnew (OpenStax) and Lance S. Lund (Anoka-Ramsey Community College) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.
