Transcript Experiment 2

Experiment 2
Qualitative Test for Elements in
Organic Compounds
Organic Compounds
• Contains the element Carbon
• Carbon’s ability to form strong covalent bond
to other carbon is the single property of
carbon atom that accounts for the existence
of the study of organic chemistry.
• It can also form strong covalent bonds with
other elements such as H, O, N, S, etc.
• Functional groups
– Is an atom or a group of atoms with characteristic
chemical and physical properties.
– Can contain heteroatom(s) and/or multiple bonds
– Determines a molecule’s shape, properties, and
the type of reactions it undergoes
– There are three types of most common functional
groups
• Hydrocarbon
• Single bond to a heteroatom
• Compounds containing C=O group
*The symbol “R” is used to represent
any carbon chains or rings
Organic Molecules and Functional Groups
Functional Groups: Hydrocarbons
Hydrocarbons are compounds made up of only the elements carbon and
hydrogen. They may be aliphatic or aromatic.
4
Organic Molecules and Functional Groups
Functional Groups:
Heteroatoms
5
Functional Groups: Carbonyl groups
Contain carbon-oxygen double
bond (C=O)
6
Experiment
•
•
•
•
•
Test for Carbon and Hydrogen
Test for Nitrogen
Test for Halogens
Test for Oxygen
Test for Sulfur
Test for Carbon and Hydrogen
• Organic compound is heated strongly with
excess of dry copper oxide in a current of dry
air and oxygen (free from CO2)
• Carbon present in the organic compound is
oxidized to CO2
C (in test compound) + 2CuO  CO2(g) + 2Cu
• Hydrogen is oxidized to water
2H (in test compound) + CuO  H2O(l) + Cu
Test for Carbon and Hydrogen
• Test compound: Glucose
Test for Carbon and Hydrogen
• Positive Result: A white precipitate forms at
the test tube with lime water and as well as
presence of droplets of water in the tube
Ca(OH)2(aq) + CO2(g)  CaCO3(s) + H2O(l)
(lime water)
Test for Nitrogen
• Also called “Soda-lime test”
• Test Sample: Urea
Test for Nitrogen
• A pinch of organic compound is heated
strongly in a dry test tube with soda lime
(NaOH + CaO)
• Positive Result: A smell of ammonia indicates
presence of nitrogen
+ NaOH(s) + CaO(s)  2NH3(g) + Na2CO3
Test for nitrogen
• Positive result: Red litmus paper changes to
blue upon exposing to vapor.
• Acid-Base reaction:
• NH3(g) + H2O(aq)  NH4+(aq) + OH-(aq)
Test for nitrogen
• Limitation:
– Soda lime test is not a reliable confirmatory test
for the presence of nitrogen since some nitrogen
containing compound such as nitro (-NO2), or azo
compounds (-N=N-)
Test for Halogens
• Beilstein Test
– A clean and bent copper wire is heated in a non
luminous flame until it ceases to impart green
flame. It is then dip in organic halide.
– Positive result: a visible blue-green flame
indicating the formation of volatile cupric halide.
– The test is used to confirm the presence of
halogens in a certain compound
Test for Halogens
• Silver Nitrate Test
– Monochloroacetic acid is reacted with silver
nitrate in the presence of hot distilled water and
nitric acid.
– Positive result: formation of white precipitate
indicating the formation of AgCl(s)
Test for Halogens
• Function of Nitric Acid
– for compound containing Nitrogen and sulfur that
may interfere with the reaction
– HNO3 decomposes the N and S in the compound
CN- + AgNO3  AgCN(s) (white precipitate)
Test for Oxygen
• Ferrox test
– Test to determine the presence of oxygen in an
organic compound ( aldehydes, ethers, ketones,
alcohols, etc.)
– Ferrox reagent:
2Fe(NH4)(SO4)2 + 6KSCN  Fe[Fe(SCN)6]
Iron (III) amm. Sulfate
Potassium
thiocyanate
Iron(III) hexathiocyanato ferrate
(III)
Test for Oxygen
• The prepared ferrox paper is dipped in the test
solution (hexane, alcohol, ether).
• Positive result: red to reddish-purple solution
upon mixing with the test sample.
• Ethanol and ether showed positive result
while hexane exhibited no change in color of
solution
Test for Sulfur
• Lead acetate test
– Albumin is a protein that consist of cystein
Test for Sulfur
• In strongly basic solution, the amino acid
cysteine will react to lead ions (Pb2+) forming
black precipitate, PbS.
• Heating is necessary to be able to break up
the polypeptide chains
• Positive Result: Black precipitate after heating
Summary
Name of the Test
Positive Result
Carbon and Hydrogen Test
Formation of white ppt. in the lime water
and droplets of water in tube
Test for Nitrogen
Ammonia odor/ red litmus paper turns to
blue
Beilstein Test
Blue-green flame
Silver Nitrate Test
White Precipitate
Ferrox Test
Red to red-purple solution
Test for Sulfur
Black precipitate upon heating