Laboratory Preparation of Hydrogen Gas: Principle and Procedure Explained with Reactions

The laboratory preparation of hydrogen gas is one of the most important experiments in chemistry that helps students understand how hydrogen is produced safely in a laboratory. Hydrogen is the lightest and most abundant element in the universe and has numerous applications in industries, laboratories and clean energy technologies. In the laboratory, hydrogen gas is commonly prepared by reacting zinc granules with dilute hydrochloric acid or dilute sulphuric acid. The gas is then collected using a suitable method because of its low density and very low solubility in water. 

This article explains the laboratory preparation of hydrogen gas in simple language, covering the principle,precautions, properties and practical applications.

Table of Contents 

• What is Laboratory Preparation of Hydrogen Gas
• Principle of Laboratory Preparation of Hydrogen Gas
• Preparation of Hydrogen Gas Using Zinc and Sodium Hydroxide
• Commercial Production of Hydrogen Gas
• Methods of Preparation of Hydrogen Gas
• Uses of Hydrogen Gas
• Precautions During the Laboratory Preparation of Hydrogen Gas
• Frequently Asked Questions on Laboratory Preparation of Hydrogen Gas

What is Laboratory Preparation of Hydrogen Gas

The laboratory preparation of hydrogen gas is a simple chemical experiment in which zinc granules react with dilute hydrochloric acid or dilute sulphuric acid to produce hydrogen gas. The reaction also forms a salt depending on the acid used.

Hydrogen is one of the most commonly prepared gases in school and college laboratories because the experiment is simple, safe when performed correctly and demonstrates an important chemical reaction between metals and acids.

General Reaction

Metal + Dilute Acid → Salt + Hydrogen Gas

Principle of Laboratory Preparation of Hydrogen Gas

The preparation of hydrogen gas is based on the reaction between an active metal and a dilute acid.

When zinc reacts with dilute hydrochloric acid or dilute sulphuric acid, zinc displaces hydrogen from the acid because it is more reactive than hydrogen. As a result, hydrogen gas is released, while a zinc salt is formed.

The hydrogen gas produced is almost insoluble in water and lighter than air, making it suitable for collection by the downward displacement of water.

Laboratory Preparation of Hydrogen Gas

Hydrogen gas is most commonly prepared in laboratories by reacting granulated zinc with dilute hydrochloric acid (HCl).

Why are Zinc Granules Used?

Zinc granules are preferred because:

• They react at a moderate and controlled rate.
• Commercial zinc usually contains traces of copper, which act as a catalyst and increase the reaction rate.
• They produce hydrogen gas efficiently without excessive heating.

Materials Required

• Granulated zinc
• Dilute hydrochloric acid (HCl)
• Conical flask
• Thistle funnel
• Delivery tube
• Water trough
• Gas collection jar

Procedure for Preparing Hydrogen Gas Using Zinc and Dilute Hydrochloric Acid

The laboratory preparation of hydrogen gas involves the following steps:

1. Place granulated zinc into a clean conical flask.
2. Add dilute hydrochloric acid slowly through a thistle funnel.
3. As the acid reacts with zinc, hydrogen gas begins to evolve immediately.
4. The hydrogen gas passes through the delivery tube into a water trough.
5. Collect the gas in an inverted gas jar by the downward displacement of water, as hydrogen is only slightly soluble in water.

Chemical Equation

$Zn + 2HCl \rightarrow ZnCl_2 + H_2 \uparrow$

Ionic Equation

$Zn + 2H^+ \rightarrow Zn^{2+} + H_2 \uparrow$

Also Read: Displacement Reaction 

Preparation of Hydrogen Gas Using Zinc and Sodium Hydroxide

Hydrogen can also be prepared by reacting zinc with hot concentrated sodium hydroxide solution. Zinc behaves as an amphoteric metal and reacts with alkalis to release hydrogen gas.

Procedure

• Heat an aqueous sodium hydroxide solution.
• Add zinc granules carefully.
• Hydrogen gas is evolved during the reaction and can be collected using the downward displacement of water.

Why is Hydrogen Collected by Downward Displacement of Water

Hydrogen is collected over water because:

• It is almost insoluble in water.
• This method prevents hydrogen from mixing with atmospheric air.
• It allows the collection of relatively pure hydrogen gas.

Hydrogen is not collected by upward displacement of air in laboratories because it can easily mix with oxygen and form an explosive mixture.

Commercial Production of Hydrogen Gas

Hydrogen is produced on a large scale to meet the demands of industries such as petroleum refining, fertilizer production, chemical manufacturing and clean energy. Several commercial methods are used depending on the source of raw materials and the desired purity.

1. Electrolysis of Brine

Hydrogen is obtained as a valuable by-product during the manufacture of sodium hydroxide and chlorine through the electrolysis of concentrated sodium chloride (brine).

Reactions

At the Anode

$2Cl^- \rightarrow Cl_2 + 2e^-$

At the Cathode

$2H_2O + 2e^- \rightarrow H_2 + 2OH^-$

Overall Reaction

$2NaCl + 2H_2O \rightarrow Cl_2 + H_2 + 2NaOH$

This process simultaneously produces:

• Hydrogen gas
• Chlorine gas
• Sodium hydroxide

2. Electrolysis of Water

Pure hydrogen can be produced by passing electricity through acidified water using platinum or inert electrodes.

Chemical Equation

$2H_2O \rightarrow 2H_2 + O_2$

This method is environmentally friendly when electricity is generated from renewable energy sources, making it an important process for producing green hydrogen.

3. Steam Reforming of Natural Gas

Steam reforming is currently the most widely used industrial method for hydrogen production.

In this process, methane reacts with steam at high temperatures in the presence of a nickel catalyst.

Chemical Equation

$CH_4 + H_2O \rightarrow CO + 3H_2$

The mixture of carbon monoxide and hydrogen produced is known as water gas or syngas (synthesis gas).

Syngas is further processed to increase hydrogen production and is widely used in the manufacture of methanol, ammonia and other industrial chemicals.

4. Electrolysis of Barium Hydroxide Solution

Hydrogen with a purity greater than 99.95% can be produced by electrolysing warm aqueous barium hydroxide solution using nickel electrodes.

This method is used when extremely pure hydrogen is required for specialised industrial and scientific applications.

Methods of Preparation of Hydrogen Gas

Method	Reactants	Main Product	Common Application
Zinc with dilute HCl	Zinc + Hydrochloric acid	Hydrogen	Laboratory preparation
Zinc with NaOH	Zinc + Sodium hydroxide	Hydrogen	Laboratory demonstration
Electrolysis of brine	Sodium chloride solution	Hydrogen, chlorine, sodium hydroxide	Chemical industries
Electrolysis of water	Water	Hydrogen and oxygen	Green hydrogen production
Steam reforming	Methane + Steam	Hydrogen and carbon monoxide	Large-scale industrial production
Electrolysis of Ba(OH)₂	Barium hydroxide solution	High-purity hydrogen	Research and specialised industries

Precautions During the Laboratory Preparation of Hydrogen Gas

Following proper safety measures is essential while preparing hydrogen gas.

• Ensure all apparatus are clean and airtight before starting the experiment.
• Allow the initial gas produced to escape because it may contain air.
• Never bring a flame near the apparatus until all the air has been removed.
• Handle dilute acids carefully and wear safety goggles and gloves.
• Use only granulated zinc for a controlled reaction.
• Collect hydrogen only after a steady stream of gas is produced.

These precautions help prevent accidents and ensure the collection of pure hydrogen gas.

Uses of Hydrogen Gas

Hydrogen is one of the most versatile industrial gases because of its high energy content and clean combustion.

Some important uses include:

• Manufacture of ammonia by the Haber process.
• Production of nitric acid through ammonia.
• Manufacture of methanol and several organic chemicals.
• Hydrogenation of vegetable oils to produce vanaspati ghee.
• Used as a rocket fuel because of its high calorific value.
• Generation of electricity in hydrogen fuel cells.
• Oxy-hydrogen flames are used for cutting and welding metals.
• Petroleum refining and removal of sulphur from fuels.
• Emerging applications in clean transportation and renewable energy storage.

Read More: Uses of Hydrogen and Uses of Hydrochloric acid 

The preparation of hydrogen gas is an important topic in chemistry that demonstrates how hydrogen can be produced through different laboratory and industrial methods. While the reaction of zinc with dilute acids is commonly used for laboratory preparation, large-scale production relies on processes such as electrolysis and steam reforming to meet industrial demands.