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6b Procedures

Autor:   •  April 3, 2011  •  Study Guide  •  618 Words (3 Pages)  •  1,551 Views

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Procedure

• If an unknown is a solid, a MP should be taken. IR spectra should be run on all unknowns.

o Determine if you have an aldehyde or ketone

o Also check for C=C or aromatic groups

• For liquids, determine BP

• Run 3 experiment simultaneously

o Compound known to give positive test, negative test, and on the unknown.

Tollens' Test (Test for aldehydes)

• Place a few mL of 10% (aq) NaOH in 4-5 clean test tubes and heat them in a water bath while preparing the Tollens' reagent.

• Place 1mL of Tollens' solution A (5% (aq) silver nitrate) in a test test tube.

• Add 0.5mL of Tollens' solution B (10% NaOH in water)

• A grey precipitate of silver oxide (Ag2O) will form

o Enough 10% (aq) ammonia should be added to dissolve the silver oxide.

• Shake the mixture

• Dilute the solution to ~5mL

• Empty the test tubes of NaOH solution, rinse them with water, and add 0.5mL of Tollens' reagent to each.

• Add 1 drop of the substance to be tested by allowing it to run down the inside of the test tube, or add ~10mg in the case of a solid.

o Set the tubes aside for a few minutes without shaking.

o If no rxn occurs, warm the mixture briefly in the water bath.

• A positive test consists of the formation of a silver mirror in the test tube.

• Waste Disposal – Add nitric acid to Tollen's reagent and neutralize with sodium carbonate

Schiff's Test (Distinguishing aldehydes from ketones)

• Add 1 drop of unknown to 0.7mL of Schiff's reagent and slightly heat the solution.

• A magenta color will appear within 10 minutes for aldehydes.

• Compare the colors produced by a known ketone and a known aldehyde.

Iodoform Test (Distinguish methyl ketones from other ketones)

• If the substance to be tested is water-soluble, dissolve 1 drop of the liquid or ~15mg of a solid unknown in 0.5mL of water in a test tube.

• Add 0.5mL of 10% (aq) NaOH and then, slowly, 0.75mL of the iodine solution.

• If the substance is

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