Lab 4: Unkowns

Question 1

What did the ignition test test for? What are its false positives/negatives?

Answer 1

Measure aromaticity and unsaturation
+ test: yellow sooty flame-> benzene/unsaturated with low H count
- test: regular flame-> saturated
false negative: large number of Oxygen atoms and unsaturated

Question 2

What did the bellstein test test for?

Answer 2

Tests for halogens
+ test: Br, Cl or I->blue/green flame
- test: yellow flame, no halogen

Question 3

What did the DNP test test for? False positives and negatives?

Answer 3

Tests for: aldehyde and ketones
+ test: unconjugated + yellow precipitate
conjugated + red precipitate
- test: light orange
false +: allylic, benzyllic OH-> easily oxidized

Question 4

What did the cerium test test for? False positives and negatives?

Answer 4

alcohols/phenols that are less than 10 carbons 
\+ test: Red-> alcohol
           green/brown->phenol
- test: light yellow
false positive: aromatic amines

Question 5

What did the solubility test test for? What is soluble in what?

Answer 5

Carboxylic acids soluble in NaHCO3
carboxylic acids and phenols soluble in NaOH
amines soluble in HCl

Question 6

If the ignition test is ambiguous, how else might u confirm whether or not u have a benzene ring in your compound?

Answer 6

You could try dissolving it in water, because it is non polar it will be insoluble

Question 7

Why does DNP give a false positive when put in glassware that had acetone?

Answer 7

Because acetone is a ketone, it will react with DNP to form a hydrazone. Acetone gives a positive DNP test

Question 8

Why use a deuterated solvent?

Answer 8

the isotope D prevents any extra peaks from occurring, so like if we used CHCl3 instead of CDcl3, we would get a huge peak because the solvent would act like it’s own compound that is being analyzed