Lab - Properties of Alcohols - Chromic Acid Test

Summary

This transcript explains the oxidation reactions of primary, secondary, and tertiary alcohols using an acid and potassium dichromate solution. The reaction changes the color from orange (Cr6+) to green (Cr3+), indicating successful oxidation. Primary alcohols oxidize to aldehydes and can further oxidize to carboxylic acids, while secondary alcohols oxidize to ketones. Tertiary alcohols, however, do not undergo oxidation, leaving the solution orange. The experiment involves testing various alcohols and recording observations of color changes to determine oxidation.

Takeaways

• 🧪 Primary and secondary alcohols can be oxidized using an oxidizing agent.
• 🔬 Potassium dichromate in sulfuric acid is a strong oxidizing agent, providing dichromate ions for the reaction.
• 🟠 The chromium ion changes from orange (Cr6+) to green (Cr3+) during the reaction, indicating oxidation.
• ✅ A color change from orange to green shows that oxidation has occurred, which is a positive test for primary and secondary alcohols.
• 👩‍🔬 Primary alcohols oxidize to aldehydes, which can further oxidize to carboxylic acids.
• 🧪 Secondary alcohols oxidize to ketones.
• ❌ Tertiary alcohols cannot be oxidized in this reaction, so no color change occurs, and the solution stays orange.
• ⚗️ The lab test involves several alcohols: water, ethanol, 2-propanol, 2-methyl-2-propanol, cyclohexanol, and salicylic acid.
• 👀 Observations should be recorded after adding a few drops of the orange acidic dichromate solution.
• 🌡️ Salicylic acid, although not typically considered an alcohol, contains a hydroxyl group and reacts similarly.

Q & A

What is an example of a good oxidizing agent used to oxidize primary and secondary alcohols?

A good oxidizing agent is a solution of sulfuric acid and potassium dichromate, which provides dichromate ions for the reaction.

What color change indicates that oxidation has taken place in the reaction with alcohols?

A color change from orange (Cr6+) to green (Cr3+) indicates that oxidation has taken place.

What is the outcome of oxidizing a primary alcohol with the test solution?

A primary alcohol is oxidized to an aldehyde, which can further be oxidized to a carboxylic acid.

What happens when a secondary alcohol reacts with the oxidizing agent?

A secondary alcohol is oxidized to a ketone, and the solution changes from orange to green.

Can a tertiary alcohol be oxidized using this test solution?

No, a tertiary alcohol cannot be oxidized with this test solution, so the solution remains orange, indicating no reaction.

What are the functional group outcomes of oxidizing primary, secondary, and tertiary alcohols?

A primary alcohol oxidizes to an aldehyde and further to a carboxylic acid, a secondary alcohol oxidizes to a ketone, and a tertiary alcohol does not undergo oxidation.

What substances are used in the lab setup for the test described in the script?

The substances used in the lab setup include water, ethanol, 2-propanol, 2-methyl-2-propanol, cyclohexanol, and salicylic acid.

Does salicylic acid contain a hydroxyl group, and how is it relevant to the test?

Yes, salicylic acid contains a hydroxyl group, making it relevant to the oxidation test, although it is not typically considered an alcohol.

What is the role of potassium dichromate in the test solution?

Potassium dichromate provides dichromate ions (Cr6+) that act as the oxidizing agent, which is reduced to Cr3+ during the oxidation of alcohols.

What should be recorded during the experiment when adding the oxidizing agent to the alcohols?

Observations regarding the color change (orange to green or no change) should be recorded to determine whether oxidation occurred.