Reactions of alkenes and alcohols (chemistry only) common mistakes

Common mistakes

• Confusing Ethanol with Other Alcohols

  Students often confuse ethanol with other alcohols and do not specify that it is produced from sugar fermentation using yeast.

  Fix itRemember to clearly identify ethanol as the specific alcohol produced in fermentation and understand the role of yeast in this process.

• Misunderstanding Fermentation Conditions

  Students often confuse the conditions for fermentation with those for other processes, such as distillation or combustion.

  Fix itFocus on the specific conditions for fermentation, which typically include a warm environment, the presence of yeast, and an anaerobic (absence of oxygen) setting.

• Misidentifying Alcohols

  Students often confuse alcohols with alkenes due to similar naming conventions.

  Fix itPay close attention to the functional group –OH in alcohols and remember that alcohols are not defined by a double bond like alkenes.

• Common Mistake in Combustion Equations

  Students often forget to balance the number of carbon, hydrogen, and oxygen atoms in the combustion equations for alcohols.

  Fix itAlways check that the number of atoms of each element is the same on both sides of the equation. Practice balancing equations step by step.

• Misunderstanding Alcohol Reactions

  Students often confuse the reactions of alcohols with those of alkenes, thinking they behave the same way in chemical reactions.

  Fix itFocus on the functional group –OH in alcohols and remember that they undergo different reactions compared to alkenes, particularly in combustion and oxidation.

• Confusing Functional Groups

  Students often confuse carboxylic acids with alcohols, thinking both contain the same functional group.

  Fix itRemember that carboxylic acids contain the –COOH functional group, while alcohols contain the –OH functional group. Focus on the distinct structures and properties of each.

• Mis‑naming the first four carboxylic acids

  Students often write the first four members of the carboxylic acid series as methanoic, ethanoic, propanoic, and butanoic acids but mistakenly use the suffix –ic acid for all, forgetting that the first acid is correctly named methanoic acid (not methanoic acid).

  Fix itRemind students that the correct systematic names are methanoic acid, ethanoic acid, propanoic acid and butanoic acid, and that the –ic acid suffix is applied to the parent alkane name (methane, ethane, propane, butane) with the –oic acid ending added.

• Misunderstanding Carboxylic Acid Representation

  Students often confuse the displayed formula of carboxylic acids with their structural formula, leading to incorrect representations.

  Fix itReview the differences between displayed and structural formulae, ensuring to practice drawing both for carboxylic acids, focusing on the –COOH functional group.

• Misunderstanding Carboxylic Acid Reactions

  Students often think that carboxylic acids react with carbonates to produce only carbon dioxide and water.

  Fix itEmphasize that the reaction also produces a salt, in addition to carbon dioxide and water, when carboxylic acids react with carbonates.

• Partial Ionisation of Carboxylic Acids

  Students often assume that carboxylic acids completely dissociate into ions when they dissolve in water, just like strong acids.

  Fix itIn reality, carboxylic acids are weak acids; when dissolved they only partially ionise, establishing an equilibrium between the undissociated acid (RCOOH) and its ions (RCOO⁻ and H⁺).