International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

Which catalyst is commonly used in the manufacture of ethanol from ethene and steam?

1. Sodium bicarbonate

2. Hydrochloric acid

3. Phosphoric acid

4. Potassium hydroxide

The correct answer is: Phosphoric acid

Phosphoric acid is commonly used as a catalyst in the hydration of ethene to produce ethanol. In this process, ethene reacts with steam at high temperatures and pressures in the presence of phosphoric acid, which facilitates the reaction without being consumed in it. The catalyst helps speed up the reaction rate and increases the yield of ethanol produced. Phosphoric acid is favored in this reaction due to its ability to provide the necessary acidic environment for the reaction to proceed efficiently. Additionally, it can operate under relatively mild conditions compared to other possible catalysts, making the process economically viable and practical for industrial applications. Other substances mentioned, such as sodium bicarbonate, hydrochloric acid, and potassium hydroxide, do not play the same role in this specific reaction. Sodium bicarbonate and potassium hydroxide are typically used as bases rather than catalysts in ethanol production, while hydrochloric acid might catalyze different types of reactions. Thus, phosphoric acid stands out as the correct catalyst for the hydration of ethene.