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Explain how the classical methods of analytical chemistry can be used to determine information about alcohols - VCE - SSCE Chemistry - Question 10 - 2020 - Paper 1
Question 10
Explain how the classical methods of analytical chemistry can be used to determine information about alcohols. In your answer, refer to: - qualitative analysis and ... show full transcript
Worked Solution & Example Answer:Explain how the classical methods of analytical chemistry can be used to determine information about alcohols - VCE - SSCE Chemistry - Question 10 - 2020 - Paper 1
Step 1
Qualitative analysis and how it can be used to determine whether a compound is an alcohol and, if it is, the type of alcohol
Answer
Qualitative analysis focuses on identifying the functional groups within a compound. To determine if a compound is an alcohol, specific reactions can be carried out:
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Reaction with Chromic Acid (CrO₃/H₂SO₄): Alcohols react with chromic acid to produce color changes.
- Primary and secondary alcohols will lead to a color shift, indicating oxidation. If there’s no color change, it may indicate a tertiary alcohol.
- This method helps distinguish between primary, secondary, and tertiary alcohols based on the reactivity.
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Bromine Test: Using Br₂ for decolorization can imply the presence of a possible alkene.
- If the product of the reaction with Br₂ shows discoloration, it implies that the compound might not be a simple alcohol, or that it may also contain other functional groups.
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pH Test: A simple pH test can indicate if the compound is an alcohol. Neutral pH can suggest that it doesn't have highly acidic or basic functional groups, thus likely being an alcohol.
Step 2
Quantitative analysis
Answer
Quantitative analysis aims to measure the amount of a substance. For alcohols, it can be determined using titration or redox reactions:
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Titration: A redox titration can be employed to determine the concentration of a known alcohol by reacting it with a titrant.
- For instance, using potassium dichromate to oxidize the alcohol will allow one to measure the volume of titrant used, which can be correlated to the concentration of the alcohol in the sample.
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Calculation of Concentration: If an alcohol is titrated and the volume of titrant used is recorded, the concentration can be calculated using: where and are the concentrations of the titrant and sample, and and are their respective volumes. This methodology gives a clear quantitative measure of the alcohol present in the sample.