The process of converting starch to ethanol is

Analysis

The question asks for the specific chemical process used to transform starch (a complex carbohydrate) into ethanol (an alcohol).

Concept Explanation

To convert starch into ethanol, the process happens in two main stages:

1. Hydrolysis: Starch is first broken down into simpler sugars (like glucose) using enzymes (such as amylase found in malt).
2. Fermentation: The glucose is then converted into ethanol and carbon(IV) oxide by the action of enzymes (zymase) present in yeast.

• Cracking refers to breaking down large hydrocarbon molecules into smaller ones (common in petroleum refining).
• Distillation is a physical process used to separate mixtures based on boiling points (often used to purify the ethanol produced after fermentation).
• Oxidation involves the loss of electrons or an increase in oxidation state (e.g., converting ethanol to ethanoic acid).

Step-by-Step Solution

1. Identify the starting material: Starch $(C_6H_{10}O_5)_n$.
2. Identify the product: Ethanol $(C_2H_5OH)$.
3. Identify the mechanism: The biological breakdown of sugars by yeast enzymes is defined as fermentation.
4. Evaluate the options: • A (Cracking) is for hydrocarbons. • B (Distillation) is for separation, not conversion. • C (Fermentation) is the biological conversion of sugars to alcohol. • D (Oxidation) is the reverse of reduction or the conversion of alcohols to acids.

The process of converting starch to ethanol is clearly defined as fermentation.

Exam Tip

Whenever you see "starch," "sugar," or "glucose" being converted into "ethanol" or "alcohol" in a chemistry question, the answer is almost always fermentation. Remember that yeast is the biological catalyst (enzyme) required for this reaction!