Lab 2 - Qualitative Analysis Flashcards
describe Benedict’s test
(what does it test for?)
(procedure?/mechanism?)
(pos/neg reactions?)
Benedict’s Test
for what?
test for reducing sugars & glucose/fructose/galactose
(monosaccharides and some disaccharides)
procedure?
ten drops of solution & ten drops of Benedict’s reagent in a test tube.
place in a high-temp (95 deg) bath for 5-10 minutes
mechanism?
tests for the presence of an aldehyde functional group -CHO
can only react to the functional group is the sugar is in a chain (has relaxed from the ring form) (bath helps it relax) (single ring forms can relax the most readily, some double ring forms can also relax)
part of Benedict’s reagent is an alkali (basic) ionic salt, which reacts with the -CHO group; this product then reacts with another part of the Benedict’s reagent, copper ions, which then form a red precipitate
results?
neg = aqua
positive = red
(can result in a spectru, indicating relative concentration:)
(green = mild positive/consider neg; yellow = in between; orange = positive)
describe Biuret test
(what does it test for?)
(procedure?/mechanism?)
(pos/neg reactions?)
Biuret Test
tests for?
proteins
(tests for presence of peptide bonds between amino acids; thus, it is not until you get to at least 3 amino acids that you will start to get a weak reaction)
procedure?
10 drops of solution and 15 drops of Biuret reagent (strong base!) into a test tube
let sit 10 minutes
mechanism?
the Biuret reagent contains a strong base and aqueous copper ions
the copper ions react with the peptides to form a purple color
at least 3 amino acids are needed for a (mild) + result; the depth of the purple correlates with the length of the amino acid chain (longer –> more purple @ 540nm absorption)
results__?
neg: blue
pos: purple
describe iodine (IKI) test
(what does it test for?)
(procedure?/mechanism?)
(pos/neg reactions?)
Iodine Test
tests for?
starch
procedure?
add 2 drops of test solution and 2 drops of IKI solution to a spot plate
mechanism?
starch molecules clump together in water
they are normally clearish/whitish
the iodine reveals the presence of starches– iodine gets trapped by the starch, turning the starches dark blue-black
results?
neg: yellow (IKI is yellow)
pos: blue/black
describe silver nitrate test
(what does it test for?)
(procedure?/mechanism?)
(pos/neg reactions?)
Silver Nitrate Test
tests for?
salts
(presence of negative ions)
procedure?
10 drops of solution in test tube with 2 drops of silver nitrate reagent
mix/make sure it’s at room temp (too hot –> precipitate might not form)
mechanism?
soluble silver nitrate + soluble salt –> white precipitate + soluble compound
ex: AgNO3 + NaCl –> AgCl (precip) + NaNO3
results?
neg: no precip
pos: white precip
describe Sudan IV test
(what does it test for?)
(procedure?/mechanism?)
(pos/neg reactions?)
Sudan IV test
tests for?
lipids/fats
procedure?
put solution in test tube
add Sudan IV dye (red powder) –> see if it dissolves
mechanism?
the Sudan IV dye is nonpolar
it will only dissolve in nonpolar substances, such as lipids/fats/oils
results?
neg: no change (precip floating on top)
pos: bright red
which test tests for the presence of lipids?
results?
Sudan IV
pos: bright red
which test tests for the presence of starch?
Iodine Test
pos: dark blue-black
which test tests for the presence of reducing sugars?
Benedict’s Test
pos: orange/red
which test tests for salts?
Silver Nitrate Test
(neg ions)
pos: white precip
which test tests for proteins?
Biuret Test
(only 3 amino acid chain or longer)
pos: purple
