Very pure hydrogen (99.9%) can be made by which of the following processes?

Wait a moment while we are looking for your question.

.

Very pure hydrogen (99.9%) can be made by which of the following processes?

Engineering

Chemistry

Hydrogen Preparation and Properties

Hydrides Preparation and Types

Preparation of Alkyl Halide

Question

Very pure hydrogen (99.9%) can be made by which of the following processes?

A

Reaction of salt like hydrides with water

B

Electrolysis of water

C

Mixing natural hydrocarbons of high molecular weight

D

Reaction of methane with steam

H₂O $\underset{}{⇌}$ H⁺ + OH^–

2H⁺ +2e^– $\overset{}{\to}$ H₂(g)

(At cathode)

2OH^– $\overset{}{\to}$ H₂O + H⁺

To understand which process produces very pure hydrogen (99.9%), let's analyze each option:

Step 1: Reaction of salt-like hydrides with water

Salt-like hydrides (e.g., NaH, CaH $H_{2}$ ) react with water to produce hydrogen gas:

$NaH + H_{2} O \to NaOH + H_{2}$

This reaction gives high-purity hydrogen because hydrides are pure compounds, and the byproduct (NaOH) can be separated easily. The hydrogen produced is typically very pure, often exceeding 99.9%.

Step 2: Electrolysis of water

Electrolysis of water involves passing an electric current through water to decompose it into hydrogen and oxygen:

$2 H_{2} O \to 2 H_{2} + O_{2}$

While this produces pure hydrogen, it may contain traces of oxygen or moisture unless carefully purified. The purity can reach 99.9% with efficient separation, but it is not as straightforward as the hydride method.

Step 3: Mixing natural hydrocarbons of high molecular weight

This process is vague, but it likely refers to steam reforming or cracking of hydrocarbons, which produces hydrogen along with other gases like CO, CO $_{2}$ , and hydrocarbons. The hydrogen requires extensive purification to achieve high purity, and it is not typically 99.9% pure directly.

Step 4: Reaction of methane with steam

This is steam methane reforming:

$CH_{4} + H_{2} O \to CO + 3 H_{2}$

Followed by the water-gas shift reaction: $CO + H_{2} O \to CO_{2} + H_{2}$

This produces hydrogen, but it is mixed with CO $_{2}$ and other impurities. High purity (99.9%) requires additional steps like pressure swing adsorption, making it less direct.

Final Answer

The reaction of salt-like hydrides with water produces very pure hydrogen (99.9%) directly because the reactants are pure, and the byproduct is easily separable, minimizing contamination.

Related Topics and Formulae

Key Concept: Production of high-purity hydrogen often involves reactions where hydrogen is generated from pure compounds with minimal byproducts. Salt-like hydrides (e.g., ionic hydrides of Group 1 and 2 metals) are excellent sources.

Relevant Formula: General reaction: $MH + H_{2} O \to MOH + H_{2}$ (where M is a metal like Na or Ca).

Theory: Salt-like hydrides release hydrogen upon hydrolysis without producing carbon-containing impurities, unlike hydrocarbon-based methods. Electrolysis can produce pure hydrogen but may require dehumidification. Steam reforming introduces carbon oxides, needing purification.