Chem 334 Lab Lecture

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Chem 334 Lab Lecture

• Expt. 28.2 part E.1
• Qualitative Analysis of Aldehydes and Ketones

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Purpose

• develop observation skills
• practice technical skills
• use deductive reasoning
• identify an unknown aldehyde or ketone
• gain an appreciation of scientists of yore

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Overall Approach

• Purify
• Distill liquids
• Recrystallize solids
• This step will not be necessary for this
  experiment.

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Overall Approach

• Measure physical properties
• Liquid
• Boiling point refractive index
• Make necessary corrections
• Review b.p. with lab instructor
• Solid
• Melting point
• Review m.p. with instructor

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Overall Approach

• Examine physical characteristics
• color
• odor
• crystal shape and size / viscosity
• anything else you notice

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Overall Approach

• Perform solubility tests
• Water Short-chain molecules (lt 5 C) or
  molecules with polar groups that can hydrogen
  bond
• HCl Amines
• NaOH Phenols and carboxylic acids
• NaHCO3 carboxylic acids
• H2SO4 everything that has oxygens or nitrogens
• This test will not be performed in lab.

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Overall Approach

• Identify functional group (chemical tests)
• DNP Test (C-3, p.561)
• positive for all ketones and aldehydes
• yellow, orange, or red precipitate

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Overall Approach

• Identify functional group (chemical tests)
• Chromic acid test (C-2, p.561)
• positive for aldehydes
• blue green or brown precipitate
• definite change from orange

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Overall Approach

• Identify functional group (chemical tests)
• Tollens test (C-11, p.565)
• positive for aldehydes
• silver mirror
• EXPLOSIVE WHEN DRY! DO NOT STORE TEST TUBE

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Overall Approach

• Identify functional group (chemical tests)
• Iodoform Test (C-6, p.563)
• positive for methyl ketones
• yellow precipitate
• Test is positive for formaldehyde.
• May be positive for methyl carbinols

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Overall Approach

• Select derivatives
• Aldehyde derivatives (Table A3, pp. 628-629)
• Ketone derivatives (Table A4, pp. 629-630)
• Narrow list of possible unknowns.
• Include compounds with melting points 5-6 above
  observed melting point.
• Include compounds with boiling points /- 5 of
  the observed corrected boiling point.

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Overall Approach

• Derivatives
• Selection guidelines
• Different melting point than unknown
• Melt between 50 and 250
• Differ 5-10 from other possible unknowns
• Must be pure and dry
• Recrystallize at least once
• Need enough material to measure melting point.

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Overall Approach

• Select derivatives

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Overall Approach

• Select derivatives

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Pre-lab Preparation

• Read Background and Expt. 28.2.
• Prepare Notebook
• Title, purpose, procedural reference
• Changes to procedure
• Work in pairs
• Solubility test will not be done
• 2,4-DNP test will not be done

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Pre-lab Preparation

• Prepare Notebook
• Table of reagents products not requried.
• Know chemical hazards of reagents
• Prepare a table to record test results.
• Pre-lab quiz

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In Lab

• Work in pairs
• Measure physical properties
• Review with lab instructor
• Run chemical tests on unknown and knowns
  simultaneously.
• Identify functional group
• Select derivatives
• Each student prepares 1 derivative

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After Lab

• Measure m.p. of derivatives
• Identify unknown