Ch.22 - Chemistry of the Nonmetals
Chapter 22, Problem 88
Complete the exercises below. Ultrapure germanium, like silicon, is used in semiconductors. Germanium of “ordinary” purity is prepared by the high-temperature reduction of GeO₂ with carbon. The Ge is converted to GeCl₄ by treatment with Cl₂ and then purified by distillation; GeCl₄ is then hydrolyzed in water to GeO₂ and reduced to the elemental form with H₂. 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 GeO₂.
Verified step by step guidance1
Step 1: Write the balanced chemical equation for the reduction of GeO₂ with carbon. The reaction involves GeO₂ reacting with carbon (C) to form germanium (Ge) and carbon dioxide (CO₂). The balanced equation is: \[ \text{GeO}_2 + \text{C} \rightarrow \text{Ge} + \text{CO}_2 \]
Step 2: Write the balanced chemical equation for the conversion of Ge to GeCl₄. Germanium (Ge) reacts with chlorine gas (Cl₂) to form germanium tetrachloride (GeCl₄). The balanced equation is: \[ \text{Ge} + 2\text{Cl}_2 \rightarrow \text{GeCl}_4 \]
Step 3: Write the balanced chemical equation for the hydrolysis of GeCl₄ to GeO₂. Germanium tetrachloride (GeCl₄) reacts with water (H₂O) to form germanium dioxide (GeO₂) and hydrochloric acid (HCl). The balanced equation is: \[ \text{GeCl}_4 + 2\text{H}_2\text{O} \rightarrow \text{GeO}_2 + 4\text{HCl} \]
Step 4: Write the balanced chemical equation for the reduction of GeO₂ with hydrogen. Germanium dioxide (GeO₂) is reduced by hydrogen gas (H₂) to form elemental germanium (Ge) and water (H₂O). The balanced equation is: \[ \text{GeO}_2 + 2\text{H}_2 \rightarrow \text{Ge} + 2\text{H}_2\text{O} \]
Step 5: Understand the concept of zone refining. Zone refining is a purification process where a solid is melted in a small region and the impurities are moved along with the molten zone, leaving behind a purer solid. This process is used to further purify the elemental germanium.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reduction Reactions
Reduction reactions involve the gain of electrons or a decrease in oxidation state by a substance. In the context of preparing ultrapure germanium, the reduction of GeO₂ with carbon is a key step, where carbon acts as a reducing agent, converting GeO₂ to elemental germanium (Ge) while itself being oxidized to carbon dioxide (CO₂). Understanding reduction is essential for writing balanced equations for these transformations.
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Oxidation and Reduction Reactions
Hydrolysis
Hydrolysis is a chemical reaction involving the reaction of a substance with water, leading to the breakdown of that substance. In this process, GeCl₄ reacts with water to form GeO₂ and hydrochloric acid (HCl). This step is crucial in the purification of germanium, as it transitions from a halide to an oxide form, which can then be further reduced to elemental germanium.
Zone Refining
Zone refining is a purification technique used to produce high-purity materials, particularly semiconductors. It involves melting a small region of a solid material and moving this molten zone along the solid, allowing impurities to be segregated into the molten phase. This method is significant in the final step of obtaining ultrapure germanium, as it enhances the purity of the elemental germanium obtained from previous chemical transformations.
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