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

What is the name of the reaction used to manufacture ethanol from ethene and steam?

1. Saponification

2. Fermentation

3. Hydration

4. Dehydration

The correct answer is: Hydration

The reaction used to manufacture ethanol from ethene and steam is referred to as hydration. During this process, ethene, which is an alkene, reacts with steam (water vapor) in the presence of a catalyst, typically phosphoric acid, to produce ethanol. This is a key industrial method because it allows for the direct addition of water to the alkene, converting the double bond of ethene into a single bond while forming the alcohol, ethanol. In this reaction, the components combine to form a higher alcohol, and since water is added to the ethene, it is specifically classified as a hydration reaction. This distinguishes it from other types of reactions that involve either the removal of water or the breakdown of substances through hydrolysis. Other options like saponification and fermentation do not apply in this context. Saponification is a process for making soap and involves the reaction of fats or oils with a base, while fermentation is a biological process involving yeast to convert sugars into ethanol. Dehydration refers to the removal of water, which is not relevant to this process where water is being added.