To determine how many moles of an alcohol are required to react with 1 mole of an aldehyde to form a hemiacetal, let's proceed step by step.
1. Understand the reaction:
- A hemiacetal is formed by the reaction of an aldehyde with an alcohol. The general reaction can be represented as:
[tex]\[ \text{RCHO (aldehyde) + R'OH (alcohol) → RCH(OH)OR' (hemiacetal)} \][/tex]
2. Mole-to-mole ratio:
- The formation of a hemiacetal involves a 1:1 mole ratio. This means that 1 mole of an aldehyde reacts with 1 mole of an alcohol to produce 1 mole of the hemiacetal.
3. Analyze the requirement:
- The question asks how many moles of alcohol are needed to react with 1 mole of an aldehyde.
4. Conclusion:
- Since the mole ratio for the reaction is 1:1, 1 mole of an alcohol is needed to react with 1 mole of an aldehyde to form a hemiacetal.
Therefore, the number of moles of alcohol needed is:
[tex]\[ \boxed{1 \text{ mole}} \][/tex]
Hence, the correct answer is 1 mole.
