Which gas is generally liberated when acid reacts with metal?

Appeared in: HSSC Staff Nurse - 2015

Explanation

The general rule for the reaction between a reactive metal and a dilute acid is that they undergo a single displacement reaction.
In this reaction, the metal displaces the hydrogen atom from the acid molecule.
This results in the formation of a corresponding metal salt and the liberation of hydrogen gas (H₂).
A classic example is the reaction of zinc (Zn) with hydrochloric acid (HCl) to form zinc chloride (ZnCl₂) and H₂ gas.

Option A: Carbon monoxide (CO) is not produced when an acid reacts with a metal. It is typically formed from the incomplete combustion of carbon-containing compounds.
Option B: Carbon dioxide (CO₂) is not produced from the reaction of an acid with a metal. The presence of carbon is necessary.
Option C: Nitrogen dioxide (NO₂) is not the general product. Its formation is an exception to the rule.

Clinical Relevance

Nursing practice connection: Knowing Chemical properties of acids, specifically their reaction with metals helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
This concept is fundamental to understanding the reactivity series of metals, which predicts which metals will react with acids to produce hydrogen.
It is a foundational principle in chemistry that explains corrosion (like rusting, which is an electrochemical process) and the functioning of batteries (galvanic cells).
What if the acid was concentrated nitric acid? Then the answer would likely be NO₂. The word 'generally' in the question stem points to the most common reaction, which is with non-oxidizing acids like HCl or dilute H₂SO₄, producing H₂.

How to Approach the Question

First, identify the core of the question: it asks for the gas produced when an acid and a metal react 'generally'. The word 'generally' is a key qualifier.
Recall the fundamental chemical properties of acids. One of the most common properties taught is their reaction with metals.
Write down the general word equation for this reaction: Metal + Acid → Salt + Gas.
Identify the specific gas produced in this standard reaction. The metal displaces hydrogen from the acid.
Therefore, the gas produced is hydrogen (H₂).
Evaluate the given options. H₂ is present. Consider the other options to confirm they are incorrect in the general case. CO₂ is from carbonates, and NO₂ is from an exceptional case (nitric acid), so H₂ is the best answer.

Concept Tested & Keywords

Concept Tested: Chemical properties of acids, specifically their reaction with metals.
Stem keywords: acid, reacts, metal, gas liberated
Lead-in keywords: Which gas, generally

QsDS_f-VEryvhFxoVwakcC

Practise the full HSSC Staff Nurse - 2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.