Exp 2.3a: Chemical Tests (Requested by Jabol Medina)

Question 1

Biuret Test:
purpose

Answer 1

detects peptide bonds

Question 2

Biuret Test:
reagents

Answer 2

NaOH & CuSO₄

Question 3

Biuret Test:
positive result

Answer 3

pink to blue to violet

Question 4

Biuret Test:
principle

Answer 4

complexation of copper with a peptide bond

Question 5

Ninhydrin Test:
purpose

Answer 5

detects free alpha-amino acids & amines

Question 6

Ninhydrin Test:
reagents

Answer 6

1,2,3-indanetrione monohydrate/ triketohydrindene & EtOH (ethanol)

Question 7

Ninhydrin Test:
positive result

Answer 7

blue or blue-purple color
proline: yellow-orange

Question 8

Ninhydrin Test:
principle

Answer 8

oxidative decarboxylation then deamination then condensation

Question 9

Xanthoproteic Test:
purpose

Answer 9

detects aromatic amino acids (Y & W)
*except F

Question 10

Xanthoproteic Test:
reagents

Answer 10

conc. HNO₃ & conc. NaOH

Question 11

Xanthoproteic Test:
positive result

Answer 11

heating: yellow solution
excess NaOH: orange

Question 12

Xanthoproteic Test:
principle

Answer 12

nitration of aromatic ring

Question 13

Millon’s Test:
purpose

Answer 13

detects phenolic group in tyrosine

Question 14

Millon’s Test:
reagents

Answer 14

HgSO₄ in H₂SO₄

Question 15

Millon’s Test:
positive result

Answer 15

old rose/ flesh/ purple-red ppt

Question 16

Millon’s Test:
principle

Answer 16

complexation (mercuration & nitration or nitrosation/ complexation of nitrohydroxyphenyl derivatives with Hg₂₊)

Question 17

Hopkins-Cole Test:
purpose

Answer 17

indole group in Tryptophan (Trp)

Question 18

Hopkins-Cole Test:
reagents

Answer 18

glyoxylic acid & conc. H₂SO₄

Question 19

Hopkins-Cole Test:
positive result

Answer 19

pink to violet interface

Question 20

Hopkins-Cole Test:
principle

Answer 20

reduction of oxalate to glyoxylate and acid-catalyzed condensation of 2 Trps with glyoxylic acid

Question 21

Sakaguchi Test:
purpose

Answer 21

guanido group of Arginine (Arg)

Question 22

Sakaguchi Test:
reagents

Answer 22

α-naphthol, NaOBr, NaOH, & urea

Question 23

Sakaguchi Test:
positive result

Answer 23

red to red-orange color

Question 24

Sakaguchi Test:
principle

Answer 24

base-catalyzed condensation of α-naphthol with the guanido group of Arginine

Question 25

Fohl's/ Lead Acetate Test: purpose

Answer 25

S-containing amino acids (M&C)

Question 26

Fohl's/ Lead Acetate Test: reagents

Answer 26

Lead (II) acetate & NaOH

Question 27

Fohl's/ Lead Acetate Test: positive result

Answer 27

brown or black ppt

Question 28

Fohl's/ Lead Acetate Test: principle

Answer 28

degradation and substitution reaction to form PbS

Question 29

Pauly's Test/ Diazo Reaction: purpose

Answer 29

detects the presence of histidine and tyrosine

Question 30

Pauly's Test/ Diazo Reaction: reagents

Answer 30

sulfanilic acid, NaNO₂, & Na₂CO₃

Question 31

Pauly's Test/ Diazo Reaction: positive result

Answer 31

red color

Question 32

Pauly's Test/ Diazo Reaction: principle

Answer 32

diazotized sulfanilic acid couple with amino phenol to form a color red azo compound in cold condition

Question 33

Nitroprusside Test: purpose

Answer 33

presence of thiol (-SH) group in Cysteine (Cys)

Question 34

Nitroprusside Test: reagents

Answer 34

Na₂Fe(CN)₅NO in dilute NH₃

Question 35

Nitroprusside Test: positive result

Answer 35

red coloration

Question 36

Nitroprusside Test: principle

Answer 36

complexation

Question 37

Amide Test: purpose

Answer 37

detects 1ᵒ, 2ᵒ, 3ᵒ amides and nitriles

Question 38

Amide Test: reagents

Answer 38

NaOH

Question 39

Amide Test: positive result

Answer 39

red litmus paper to blue (basic)

Question 40

Amide Test: principle

Answer 40

base-catalyzed hydrolysis