Problem 88 - Chemistry The Central Science In Si Units

Question

Ultrapure germanium, like silicon, is used in semiconductors. Germanium of "ordinary" purity is prepared by the high-temperature reduction of \(\mathrm{GeO}_{2}\) with carbon. The Ge is converted to \(\mathrm{GeCl}_{4}\) by treatment with \(\mathrm{Cl}_{2}\) and then purified by distillation; \(\mathrm{GeCl}_{4}\) is then hydrolyzed in water to \(\mathrm{GeO}_{2}\) and reduced to the elemental form with \(\mathrm{H}_{2}\). The element is then zone refined. Write a balanced chemical equation for each of the chemical transformations in the course of forming ultrapure Ge from \(\mathrm{GeO}_{2}\).

Step-by-Step Solution

Answer

Transform "GeO_2" to ultrapure Ge through reduction, chlorination, hydrolysis, and further reduction.

Step 1: Reduction of Germanium(IV) oxide

The first step involves the reduction of \( \text{GeO}_2 \) with carbon. The balanced chemical equation for this process is: - \[ \text{GeO}_2 (s) + 2\text{C} (s) \rightarrow \text{Ge} (s) + 2\text{CO} (g) \] This reaction involves the conversion of germanium oxide to germanium and carbon monoxide at high temperatures.

Step 2: Conversion to Germanium Tetrachloride

Next, germanium is converted to germanium tetrachloride by reacting with chlorine gas. The equation for this transformation is: - \[ \text{Ge} (s) + 2\text{Cl}_2 (g) \rightarrow \text{GeCl}_4 (g) \] This reaction synthesizes \( \text{GeCl}_4 \), which is later purified by distillation.

Step 3: Hydrolysis of Germanium Tetrachloride

The purified \( \text{GeCl}_4 \) undergoes hydrolysis when added to water, yielding \( \text{GeO}_2 \) and HCl: - \[ \text{GeCl}_4 (g) + 2\text{H}_2\text{O} (l) \rightarrow \text{GeO}_2 (s) + 4\text{HCl} (aq) \] This reaction reverses the chloride formation, producing germanium dioxide again.

Step 4: Reduction of Germanium(IV) oxide to Elemental Germanium

Finally, \( \text{GeO}_2 \) is reduced to elemental germanium using hydrogen. The equation is: - \[ \text{GeO}_2 (s) + 2\text{H}_2 (g) \rightarrow \text{Ge} (s) + 2\text{H}_2\text{O} (g) \] This step results in the production of ultrapure germanium.

Key Concepts

Semiconductors

Semiconductors are materials used in modern electronics that have electrical conductivity between that of a conductor such as copper and an insulator like glass. In semiconductor devices, their conductivity can be precisely altered by adding impurities, known as doping.
Ultrapure germanium is critical in semiconductor technology due to its ability to efficiently conduct electricity under controlled conditions. Germanium's ability to switch between conducting states makes it ideal for use in transistors and other electronic components that rely on controlled flow of electricity.

Germanium, like silicon, has applications in various electronic devices due to its semiconductor properties. These properties are mainly attributed to its crystal structure and the number of valence electrons, which allow it to easily gain or lose electrons.

Chemical equations

Chemical equations describe the transformation of reactants into products. They must be balanced to obey the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction. In germanium purification, several chemical transformations occur, each represented by a balanced equation.

• Reduction of germanium dioxide:
  
  
  
  
  
  
  
  
  ** Summary** - Ensure that every atom present is accounted for in both reactants and products.
  
  The principles of chemical equations are foundational to understanding reactions and necessary adjustments to achieve ultrapure substances

Reduction reactions

Reduction reactions involve the gain of electrons by a molecule, atom, or ion. In the context of germanium purification, the reduction of germanium dioxide (\( \text{GeO}_2 \)) is essential to convert the oxide form to elemental germanium (\( \text{Ge} \)).

This process occurs in two key steps:

• The first reduction uses carbon to transform \( \text{GeO}_2 \) into elemental germanium:
  
  
  At high temperatures, carbon acts as the reducing agent, providing electrons and shifting the oxidation state of germanium from +4 in \( \text{GeO}_2 \) to 0 in \( \text{Ge} \).


• The second reduction employs hydrogen, further purifying the germanium:
  The hydrogen serves as the reducing agent, effectively removing oxygen from \( \text{GeO}_2 \).

Each reduction with carbon and hydrogen is crucial for removing impurities and achieving the desired purity in the final germanium product.

Chemical transformations

Chemical transformations refer to the changes that occur during chemical reactions where substances are converted into different substances. In germanium purification, these transformations are vital for achieving ultrapure germanium.

The key transformations in the process include:

• Initial reduction of \( \text{GeO}_2 \) to elemental germanium using carbon.
• Formation of \( \text{GeCl}_4 \) by reacting germanium with chlorine gas. This step ensures further purification via distillation.
• Hydrolysis of \( \text{GeCl}_4 \), which converts it back to \( \text{GeO}_2 \) while also generating HCl as a byproduct.
• Final reduction with hydrogen, leading to ultrapure elemental germanium.

Each transformation must be precisely controlled to maintain high-purity levels, necessary for the effective use of germanium in semiconductors.