Problem 87 - Chemistry The Central Science

Question

Ultrapure germanium, like silicon, is used in semiconductors. Germanium of "ordinary" purity is prepared by the hightemperature 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

The balanced chemical equations for the formation of ultrapure Ge from GeO₂ are as follows: 1. Reduction of GeO₂ with carbon: \[ \mathrm{GeO}_2 + \mathrm{C} \rightarrow \mathrm{Ge} + \mathrm{CO}_2 \] 2. Conversion of Ge to GeCl₄: \[ \mathrm{Ge} + 2\,\mathrm{Cl}_2 \rightarrow \mathrm{GeCl}_4 \] 4. Hydrolysis of GeCl₄ in water: \[ \mathrm{GeCl}_4 + 2\,\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{GeO}_2 + 4\,\mathrm{HCl} \] 5. Reduction of GeO₂ with hydrogen: \[ \mathrm{GeO}_2 + 2\,\mathrm{H}_2 \rightarrow \mathrm{Ge} + 2\,\mathrm{H}_2\mathrm{O} \]

Step 1: Reduction of GeO2 with carbon

In this step, GeO2 is reacted with carbon (C) at high temperature to produce Ge and carbon dioxide (CO2). The balanced chemical equation for this reaction is: \[ \mathrm{GeO}_2 + \mathrm{C} \rightarrow \mathrm{Ge} + \mathrm{CO}_2 \]

Step 2: Conversion of Ge to GeCl4

In this step, Ge is treated with chlorine gas (Cl2) to form germanium tetrachloride (GeCl4). The balanced chemical equation for this reaction is: \[ \mathrm{Ge} + 2\,\mathrm{Cl}_2 \rightarrow \mathrm{GeCl}_4 \]

Step 3: Purification of GeCl4 by distillation

GeCl4 is purified by distillation, but there is no chemical reaction happening in this step. Hence, no balanced equation is needed for this step.

Step 4: Hydrolysis of GeCl4 in water

In this step, GeCl4 reacts with water (H2O) to form germanium dioxide (GeO2) and hydrochloric acid (HCl). The balanced chemical equation for this reaction is: \[ \mathrm{GeCl}_4 + 2\,\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{GeO}_2 + 4\,\mathrm{HCl} \]

Step 5: Reduction of GeO2 with hydrogen

In this step, GeO2 is reduced to elemental germanium (Ge) by reacting with hydrogen gas (H2). The balanced chemical equation for this reaction is: \[ \mathrm{GeO}_2 + 2\,\mathrm{H}_2 \rightarrow \mathrm{Ge} + 2\,\mathrm{H}_2\mathrm{O} \]

Step 6: Zone refining of elemental Ge

Zone refining is a physical process and does not involve any chemical reaction. Therefore, no balanced equation is needed for this step. In summary, the complete process of forming ultrapure germanium from germanium dioxide involves several chemical reactions and purification steps. The balanced equations for these transformations are presented in Steps 1, 2, 4, and 5.

Key Concepts

Chemical Equations

Chemical equations are a crucial part of describing chemical transformations. They show what happens during a reaction and represent the reactants and products. In the purification of germanium, several key reactions occur, each of which can be represented by a balanced chemical equation:

• Reduction of GeO2 with Carbon: This step involves germanium dioxide reacting with carbon to form elemental germanium and carbon dioxide. It's represented as: \[ \mathrm{GeO}_2 + \mathrm{C} \rightarrow \mathrm{Ge} + \mathrm{CO}_2 \] This equation indicates how the oxygen in GeO2 combines with carbon to form CO2, thus isolating Ge in its elemental state.
• Formation of GeCl4: The elemental germanium reacts with chlorine: \[ \mathrm{Ge} + 2\,\mathrm{Cl}_2 \rightarrow \mathrm{GeCl}_4 \] Here, germanium bonds with chlorine to form germanium tetrachloride, a volatile compound.
• Hydrolysis of GeCl4: GeCl4 is converted back to GeO2 and hydrochloric acid: \[ \mathrm{GeCl}_4 + 2\,\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{GeO}_2 + 4\,\mathrm{HCl} \] Water breaks the bonds in GeCl4, resulting in GeO2 and HCl.
• Reduction with Hydrogen: Finally, GeO2 is reduced again, but this time with hydrogen: \[ \mathrm{GeO}_2 + 2\,\mathrm{H}_2 \rightarrow \mathrm{Ge} + 2\,\mathrm{H}_2\mathrm{O} \] This reaction gives us pure germanium, ready for the next step of zone refining.

Semiconductors

Semiconductors are materials with electrical conductivity between conductors and insulators. Germanium, like silicon, is a semiconductor, making it invaluable in electronics.

• Characteristics: Semiconductors have a unique property: their conductivity can be precisely controlled through doping and temperature. This makes them perfect for creating integrated circuits and transistors.
• Germanium's Role: Apart from silicon, germanium is another key element used in semiconductors due to its high electron mobility. This means electrons can move more freely through germanium than some other materials, allowing for faster electronic device functioning.
• Applications: Germanium is used in high-speed electronics and optical devices. It has significant applications in infrared optics and solar cells, where its properties are advantageous.

The purification process ensures that germanium used in semiconductors is free from impurities that could affect its performance.

Zone Refining

Zone refining is a technique used to purify materials, like germanium, by removing impurities.

• Process: Achieving high purity requires melting a small region of germanium and gradually moving this molten zone along the ingot. As it moves, the molten zone collects impurities, which then concentrate at one end of the ingot.
• Principle: The method relies on the fact that impurities tend to concentrate in the liquid phase rather than the solid crystal. Thus, as the melting zone moves, impurities are carried away with it.
• Advantages: Zone refining is critical for semiconductor manufacturing, as it can reduce impurity levels significantly without introducing additional contamination. This process is non-chemical and depends on precise heating methods.

High-Temperature Reduction

High-temperature reduction is a chemical process used to extract metals from their ores. For germanium, it involves reducing germanium dioxide (\( \mathrm{GeO}_2 \)):

• How it Works: By applying heat, carbon reduces GeO2, forming germanium and carbon dioxide. This is a key step in extracting germanium in its elemental form: \[ \mathrm{GeO}_2 + \mathrm{C} \rightarrow \mathrm{Ge} + \mathrm{CO}_2 \]
• Temperature Importance: High temperatures are crucial as they drive the reaction forward by providing the energy needed to break bonds in the reactants and form new products.
• Significance: By using high temperature, the reduction process ensures that germanium is produced in a form suitable for further purification and use in semiconductors.

This process is a chemical route to produce the desired elemental germanium critical for technological applications.