identifikasi analit

IDENTIFIKASI ANALIT

The general procedure for separating ions in qualitative analysis

Add precipitating

ionCe

ntrif

uge

Add precipitating

ion

Cent

rifug

e

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

A qualitative analysis scheme for separating cations into five ion groups

Add 6M HCl

Cent

rifug

eAcidify to

pH 0.5; add H2S

Cent

rifug

e

Add NH3/NH4

+ buffer(pH 8)

Cent

rifug

e

Add (NH4)2HPO4

Cent

rifug

e


Step 1 Add

NH3(aq)

Cent

rifug

e

Cent

rifug

e

Step 2 Add HCl

Step 3 Add NaOH

Cent

rifug

eStep 4 Add

HCl, Na2HPO4

Step 5 Dissolve in

HCl and add KSCN

A qualitative analysis scheme for Ag+,Al3+,Cu2+, and Fe3+


Spot Tests: Another Qualitative Analysis

Spot Tests: Another Qualitative Analysis

• Purpose To identify several ions present in an unknown mixture:

Cl- (chloride), SCN- (thiocyanate), C2H3O2- (acetate),

PO43- (phosphate), CO3

2- (carbonate), CrO42-

(chromate),

SO42- (sulfate), and NH4

+ (ammonium).

This analysis differs from other Qualitative Analysis experiments because we are not separating the ions from the mixture, therefore interferences between ions need to be considered.

Spot Tests

• Test 1: Carbonate Ion

• You will first test the “known” solution by placing 5 drops of the 1 M Na2CO3 solution in a micro test tube (or spot plate) and add 5 drops of 6 M HCl. The formation of bubbles indicates release of carbon dioxide gas.

• Repeat the test using 5 drops of your

unknown and adding 5 drops of 6 M HCl (do NOT add the 1 M Na2CO3 solution as this is the “known” solution).

Spot Tests• Test 2: Thiocyanate Ion

• This basis of the thiocyanate spot test is to identify the thiocyanate ion, SCN- , by its reaction with iron(III) to form a blood-red colored complex. Add 5 drops of 6 M HCl to 5 drops of 0.5 M KSCN (the “known”) on the spot plate. Add 1 drop of 0.1 M Fe(NO3)3 to the solution in the spot plate. The solution will turn red if SCN- is present.

• Repeat the test on your unknown solution without adding the “known” 0.5 M KSCN solution.

Spot Tests• Test 3: Sulfate Ion

• Put 5 drops of the “known” 0.5 M Na2SO4 solution in a well of a spot plate. Add 5 drops of 6 M HCl to the plate. Now add 1 drop of 1 M BaCl2 to the plate. A precipitate of white BaSO4 indicates the presence of sulfate ion.

• Repeat the test on your unknown without using the 0.5 M Na2SO4 “known” solution.

Spot Tests• Test 4: Phosphate Ion

• Place 5 drops of the “known” 0.5 M Na2HPO4 (sodium monohydrogen phosphate) solution in a medium test tube. Add 1 mL of 6 M HNO3. Now add 1 mL of Ammonium molybdate solution, (NH4)2MoO4 to the test tube. The presence of phosphate ions is confirmed by the formation of a yellow precipitate.

• This precipitate is often slow to form and heating in the hot water bath may be required to initiate precipitation.

• Repeat the test on your unknown.

Spot Tests• Test 5: Chromate Ion

• Solutions containing chromate ions are yellow when neutral or basic and orange when acidic. The orange color is due to the formation of the dichromate ion (Cr2O7

2-).

• Add 5 drops of “known” 0.5 M K2CrO4 to a spot plate. Add 5 drops of 3% H2O2. Now add 10 drops of 6 M HNO3 to the plate. The formation of a blue-green color, which appears but rapidly disappears, indicates the presence of the chromate ion.

• Repeat this test on your unknown without adding the 0.5 M K2CrO4 “known” solution.

Spot Tests• Test 6: Chloride Ion

• Place 5 drops of “known” 0.5 M NaCl on a spot plate. Add 5 drops of 6 M HNO3. Now add 2 drops of 0.1 M AgNO3 to the plate. The presence of chloride ion is indicated by the formation of a white precipitate of AgCl.

• If Test 2 indicated that your unknown contained SCN-, follow the lab manual procedure for removing the SCN- ion before you test your unknown for Cl- because SCN- also forms a white precipitate with Ag+.

• Repeat this test on your unknown solution. Remember not to add the “known” NaCl solution.

Spot Tests• Test 7: Acetate Ion

• Place 5 drops of “known” 0.5 M NaC2H3O2 (sodium acetate) on a spot plate. (The acetate ion is often abbreviated as OAc-, or as CH3COO-). Add 5 drops of 3 M H2SO4 to the spot plate. The presence of acetate ion is indicated by the smell of acetic acid (a vinegar odor) coming from the plate. If no odor is immediately present, repeat the test in a micro test tube, warming it in a hot water bath for 20 seconds and check the odor again.

• Repeat this test on your unknown solution. Do not add the “known” NaC2H3O2 solution.

Spot Tests• Test 8: Ammonium Ion

• This test also relies on your sense of smell to detect the presence of a substance. Add 5 drops of “known” 0.5 M NH4Cl to a spot plate or a micro test tube. Add 5 drops of 6 M NaOH to the plate and check for the presence of an ammonia odor by gentle wafting. If no odor is immediately apparent, warm the test tube and check again.

• As an additional test for NH4+, place a drop of

the unknown on a spot plate and add a drop of Nessler’s Reagent. A reddish-brown precipitate indicates the presence of the NH4

+ ion (see lower photo).

• Repeat the test on your unknown.

Spot Tests

• Interfering Ions

• If you suspect that an ion is interfering with a particular test, make up a “known” solution that contains the ions you think you have in our unknown and repeat the spot tests which gave you trouble.

• Test 3 is most likely to have interference problems from the Ba2+ ion which also forms precipitates with the chromium and phosphate ions.

• Test 6 is most likely to have interference problems from the Ag+ ion which forms precipitates with the phosphate, sulfate, carbonate, chromate, and thiocyanate ions.

Organic Qualitative Analysis

Physical Properties, Chemical tests and Infrared Spectroscopy to Identify:

Unknown Halide (primary, secondary, tertiary)Hydrocarbon (alkane, alkene, aromatic)Alcohol (primary, secondary, tertiary)

References:Slayden, S., Stalick, W.; 2010, Catalyst - Organic Chemistry Laboratory Manual, GMU Print ServicesPavia, D., Lampman, G., Kriz, G, Engel, R, 2010, A Small Scale Approach to Organic Laboratory Techniques, 3nd ed, Cengage Learning

04/17/2023 16

Organic Qualitative Analysis• Purpose: Become familiar with a combination of physical and

chemical tests for characterizing classes of organic compounds. To use these tests plus Refractive Index and IR to identify an unknown.

• Classes: Compounds without a Carbonyl group or Nitrogen group

– Alkanes

C-C– Alkenes

C=C– Alkynes

C≡C– Aromatics

C=C– Alkyl (1o, 2o, 3o) & Aryl Halides

R-X– Alcohols (1o, 2o, 3o)

R-OHNote: Tests for carbonyl based compounds (Aldehydes & Ketones) will be presented next semester

04/17/2023 17

Organic Qualitative Analysis• The Tests – Compound Classes

Test Compound Class

• Solubility Relative to H2O & H2SO4 All• Density Relative to H2O All• Beilstein (Flame) Halides• Silver Nitrate/Ethanol Alkyl & Aryl

Halides• Sodium Iodide/Acetone Alkyl & Aryl

Halides• Bromine/Methylene Chloride Unsaturated

C=C CC• KMnO4 (Baeyer Test) Unsaturated

C=C CC• Ignition Aromaticity

C=C• Acetyl Chloride Alcohols• Lucas Test Alcohols• Chromic Acid Alcohols

04/17/2023 18

Organic Qualitative Analysis• The Tests – Test References

(Pavia (3rd ed) – GMU Version or Pavia Main text as indicated)

– Test Page No.– Solubility Relative to H2O & H2SO4 p. 453-458– Density Relative H2O p. 717-719

Beilstein (Flame) p. 459-460– Silver Nitrate/Ethanol P. 460-461– Sodium Iodide/Acetone p. 158 Pavia Main

Text– Bromine/Methylene Chloride p. 464-466– KMnO4 (Baeyer Test) p. 466-467– Ignition p. 467-468– Acetyl Chloride p. 585– Lucas Test p. 585– Chromic Acid p. 586-48704/17/2023 19

Organic Qualitative Analysis• Elements of the Experiment - Week One

Boiling Point & Purification (Simple Distillation) Physical Characteristics of Unknown Solubility Relative to Water & Conc H2SO4

(Just the unknown) – Page 453

Density relative to Water (Just the unknown)

Refractive Index (unknown only) Temperature Correction for Refractive Index Beilstein Test (Halides) – Page

459 Ignition Test (Aromaticity) – Page

46704/17/2023 20

Organic Qualitative Analysis• Elements of the Experiment – Week Two

Test Compound Class Ref

– Silver Nitrate/Ethanol Alkyl & Aryl Halides p. 460

– Sodium Iodide/Acetone Alkyl & Aryl HalidesNote: This experiment is not in the GMU Pavia text, but is

in the regular hard cover Pavia Text p. 158– Bromine/Methylene Chloride Unsaturated C=C CC p.

465– KMnO4 (Baeyer Test) Unsaturated C=C CC p.

466– Acetyl Chloride Alcohols p.

485– Lucas Test Alcohols p.

485– Chromic Acid Alcohols p.

486– IR Spectra p.

851

04/17/2023 21

Organic Qualitative Analysis• General Notes

– Dangerous Chemicals – Acetyl Chloride, Conc H2SO4 Use Gloves, Goggles, and Lab Coat (Buttoned)

– Use a test tube rack from cabinet

– Use medicine droppers from equipment set

Pasteur pipettes are not available

– Make sure to wash and dry the medicine dropper and test tubes for each test

04/17/2023 22


General Notes– The Beilstein (flame) Test for Halides and the Ignition test

for Aromaticity with be done in the hood with the assistance of the instructor

– Record the results of the chemical tests in a 5-column table created in the prelab template (see slide 11)

– Use simple, direct language to describe your test.It is very important to describe an observation completely

Ex. The Unknown was soluble in water

– Be sure to obtain a good positive result for each test; repeat the test until a good positive result is obtained

04/17/2023 23

Organic Qualitative Analysis• Testing Sequence for Knowns & Unknown

– The Boiling Point, Solubility, Refractive Index, Flame test, and IR should indicate the general class of the unknown compound – Halogen, Hydrocarbon, Alcohol

– Test your unknown and all the known compounds against only those tests for which the compounds are applicable, e.g., Sodium Iodide & Silver Nitrate for Halides; KMnO4 & Bromine in Methylene Chloride for Hydrocarbons, Lucas, Acetyl Chloride for alcohols

For each test, set up a sufficient number of test tubes to accommodate the unknown and the applicable number of knowns for that test

• Add test reagent• Add compound to be tested; shake mixture• Heat reaction mixture if specified in test directions

04/17/2023 24

Organic Qualitative Analysis• The Report

– Each “Test” is a Procedure and must be set up with:• A Title• Materials & Equipment, including reagents, known and

unknown compounds, test tubes• Procedure Description in bullet format• Test Results – include a 5-column table (see next slide)

containing the name of the compound, your observations, and an indication of whether a result for a givent compound was positive or negative relative to the compound tested and the test applied

– Summary – All results summarized in a paragraph– Analysis & Conclusions

• Arguments showing how your results support your identification of the unknown

04/17/2023 25


• Suggested table for recording Qualitative Organic test results (Create your own, don’t copy)

04/17/2023 26

Compound Observation(Rm Temp)

Observation50oC

Observation100oC

Was ResultExpected?

Unknown

Known #1

Known #2

Known #3

Organic Qualitative AnalysisSolubility Test

(Water (H2O) and Conc Sulfuric Acid (H2SO4)

• Only the unknown is to be tested for solubility inWater and Concentrated Sulfuric Acid– Water

• Compounds with <5 Carbons containing O, N, S are soluble

• Compounds with 5-6 Carbons containing O, N, S are borderline (slightly soluble)

• Branching Alkyl chains result in lower melting/boiling points and increased solubility

• Increase N, O, S to Carbon ratio increases solubility

04/17/2023 27



• Conc H2SO4 Solubility– Compounds containing N, O, S can be protonated in

Conc H2SO4 and thus are considered soluble.– Alkenes (C=C)– Alkynes (C≡C)– Ethers (C-O-C)– Nitroaromatics (Nitrobenzene)– Amides– Alcohols (R-OH)– Ketones– Aldehydes– Esters

04/17/2023 28



• Water & Conc H2SO4 Solubility– Not soluble

• Alkanes• Aromatic Hydrocarbons• Alkyl Halides• Aromatic Halides

04/17/2023 29


Relative Solubility & Density• Procedure – Water & H2SO4

Note: Solubility & Density test is performed only on the Unknown

– Place about 2 mL of Distilled Water or Conc H2SO4 in a test tube

– Add 3-5 drops of the compound to be tested– Shake vigorously– Solubility is indicated by a “single” clear liquid, i.e. no

bubble or additional layers– Production of a gas, a change in color, and/or a change in

temperature indicates a chemical reaction; thus, solubility

04/17/2023 30


Relative Solubility & Density (Con’t)• Procedure Water & H2SO4 (Con’t)

Density relative to water of an insoluble compound is indicated by where the insoluble compound settles:

top (less dense)suspended (similar density)bottom (more dense)

Solubility of a hydrocarbon in water indicates 4 or less carbons

04/17/2023 31

Organic Qualitative AnalysisBeilstein Test (General for Halides)

• Procedure– Bend small loop in the end of piece of copper wire.– Heat loop in Bunsen Burner– After cooling

Liquid sample: dip wire in sample. Solid sample: dip wire in water then sample.

– Heat wire Compound first burns with yellow flame. After burning for a few seconds, a green flame is

produced if a halogen is present– Does not differentiate between Chlorine, Bromine, or

Iodine– Weak color could indicate present of impurities in a non-

halide sample04/17/2023 32

Organic Qualitative AnalysisSilver Nitrate in Ethanol Test (Sn1 for Halides)

• Does not distinguish between Chloride, Bromine, or Iodine• Sn1 (nucleophilic substitution) reactions depend on:

– Weak Nucleophile (NO3)– Polar Solvent (Ethanol)– Compounds equipped with good leaving groups (H2O, CL,

Br, I)• The Halide (leaving group) is replaced with the nitrate

nucleophile forming an insoluble white precipitate – The degree of precipitate formation is dependent on the

relative stability of the compound and the resulting Carbocation that forms in the reaction

Benzyl Allyl > Tertiary (3o) > Secondary (2o)> Primary (1o) > Methyl > Vinyl > Aryl (Aromatic)

04/17/2023 33


Silver Nitrate in Ethanol Test (Sn1 for Halides)• The Test

– Add 1 to 2 drops of liquid sample (or 5 drops of concentrated Ethanoic solution of a solid sample) to 2 mL of 2% Ethanoic Silver Nitrate

– Positive test – cloudy to heavy white precipitate depending on relative stability of Carbocation• Allyl, Benzyl, Tertiary Halides give white precipitate at

room temperature• Primary & Secondary Alkyl Halides test positive (usually

cloudy ppt) when heated (100oC)• Aromatic and many Vinyl Substituted Halides do not give

positive tests

04/17/2023 34

Organic Qualitative AnalysisSodium Iodide in Acetone (Sn2 for Alkyl Halides) Sodium Iodide is soluble in Acetone, but Sodium Chloride and

Sodium Bromide are not soluble The Iodide ion is an excellent Nucleophile – A Lewis Base with

a pair of unshared electrons that seeks a positive part of an atom

Acetone is a non-polar solvent Alkyl Chlorides and Bromides would react with the Sodium

Iodide in an Sn2 reaction in which the Chloride & Bromide ions are replaced with the Iodine atoms

The reaction equilibrium is continuously forced to the right as the NaCl & NaBr precipitate in acetone

As the reactivity of the Halide becomes less reactive (Benzyl and Aromatic) precipitation ceases

04/17/2023 35

Organic Qualitative AnalysisSodium Iodide in Acetone (Sn2 for Alkyl Halides)

• Relative Halide reactivity for an Sn2 reaction is the opposite of an Sn1 reaction, that is:

Vinyl > Methyl > Primary (1o) > Secondary (2o) > Tertiary (3o) > Allyl Benzyl Aryl (Aromatic)

Note: Aryl (Aromatic) Halides are unreactive for both Sodium Iodide (Sn2) and Silver Nitrate (Sn1) tests

Primary Alkyl Halides will give an immediate precipitate at room temperature

Secondary Alkyl Halides will give a cloudy precipitate when heated to 50oC and then cooled

Tertiary Alkyl Halides will also give a precipitate when heated to 50oC and then cooled

Aryl Halides, like Chlorobenzene, will not give a precipitate, even after heating

04/17/2023 36

Organic Qualitative AnalysisSodium Iodide in Acetone (Sn2 for Alkyl Halides)• The Test

– Add 6-8 drops of sample to 2mL of the 15% Sodium Iodide (NaI) in Acetone solution and shake gently

– Positive Test is a white or cloudy white precipitate– If a precipitate forms but disappears with mild shaking, the

instructor may suggest adding additional sample– Record the observed results at room temperature– If no precipitate forms, heat solution in a water bath (maximum

50oC) for 1 minute and cool solution to room temperature– Observe results– Record results for both room temperature and at 50oC

04/17/2023 37

Organic Qualitative AnalysisBromine in Methylene Chloride (Simple Multiple Bonds)

• Addition reaction of Bromine (Br2), a red liquid, to a compound containing a double or triple bond produces a colorless Dibromide

• The double (or triple bond) must be sufficiently electron-rich to initiate the reaction. Therefore, minimal electron withdrawing groups (Deactivators), such as Carboxyl Groups attached to molecule, would hinder the reaction

• Unsubstituted Aromatic compounds do not react with the Bromine reagent

• Even if the ring has substituted activating groups (donate electrons to the ring) the reaction would be a substitution and not an addition

04/17/2023 38

Organic Qualitative AnalysisBromine in Methylene Chloride

• The Test– If sample is a solid, add 50 mg of a solid sample to

1 mL Methylene Chloride in a test tube– If sample is a liquid, add 2 mL of liquid sample directly to

test tube

– Add 2% Bromine solution (Br2 & Methylene Chloride) dropwise to the test tube and shake solution

– The test is positive for presence of double or triple bonds if 5 drops of Bromine decolorize the solution

– If HBr is evolved, the test is negative indicating a substitution reaction, instead of an addition reaction, i.e., there are no double or triple bonds present

04/17/2023 39


Potassium Permanganate (Baeyer) Test(double or triple bonds)

• Potassium Permanganate (KMnO4) is an oxidizing agent.

• It has a Purple color• Following the oxidation of an unsaturated compound, the

Permanganate ion is reduced to Manganese Dioxide (MnO2), a brown precipitate

Note: Other easily oxidized compounds – Aldehydes, some Alcohols, Phenols, and Aromatic Amines – should be accounted for in your analysis

04/17/2023 40


Potassium Permanganate (Baeyer) Test(double or triple bonds)

• The Test– Dissolve 25 mg a solid sample or two drops of a liquid sample in

1-2 mL of one of the following solvents:• Water (if soluble, skip Ethanol & Dimethoxymethane)• 95% Ethanol (if soluble, skip Dimethoxymethane)• 1,2-Dimethoxymethane

– Slowly add 1% aqueous solution Potassium Permanganate, drop by drop, while shaking (usually just one drop works)

– If the purple MnO4-1 ion is reduced to Manganese Dioxide

(MnO2), a brown precipitate, the test is positive for double or triple bonds, but not Aromatic rings

04/17/2023 41

Organic Qualitative AnalysisIgnition (Aromaticity)

(=C-H bonds in Aromatic rings)• The Test

– In a hood, place a small amount of the compound on a spatula and place it in the flame of a Bunsen burner

– Positive test is a sooty yellow flameNote: The Sooty flame usually comes off fairly

quickly. Look for it moving quickly away and upward from the yellow/blue flame area

– Positive test is indicative of a high degree of Unsaturation and is probably Aromatic

04/17/2023 42


Acetyl Chloride (Alcohols)• Acid Chlorides react with Alcohols to form esters• Acetyl Chloride forms Acetate esters• This test does not work well with solid alcohols• Phenols also react with Acetyl Chloride and should be

eliminated prior to testing for Alcohols• Amines also react with Acetyl Chloride to produce heat and

also should be eliminated prior to testing

04/17/2023 43


Acetyl Chloride (Alcohols)• The Test

– Cautiously add 10-15 drops of Acetyl Chloride, drop by drop, to about 0.5 mL of liquid sample

– Positive test is evolution of Heat and Hydrogen Chloride (HCl) gas

– Addition of water will sometimes precipitate the ester, further confirming the test

04/17/2023 44


Lucas Test (Alcohols)

• Primary Alcohols dissolve in reagent giving clear solution

• Secondary Alcohols produce cloudiness after about 3-5 minutes. May need to heat slightly

• Tertiary, Benzylic, and Allylic alcohols produce immediate cloudiness; eventually, an immiscible Alkyl Halide separates into a separate layer

04/17/2023 45


Lucas Test (Alcohols)• The Test

– Reagent – Conc HCL + Anhydrous Zinc Chloride– Lucas test does not work well with solid alcohols– Place 2 mL Lucas Reagent in small test tube.– Add 3-4 drops of liquid sample; shake vigorously

04/17/2023 46


Chromic Acid (Alcohols)• Chromic Acid (Cr+6) oxidizes Primary and Secondary Alcohols

to Carboxylic Acids and Ketones, respectively• Chromium (+6) is reduced to Chromium (+3)

The color change is from orange to green• Tertiary Alcohols do not react with Chromic Acid• Distinguish Primary & Secondary Alcohols from Tertiary

Alcohols

04/17/2023 47


• The Reaction

04/17/2023 48


Chromic Acid (Alcohols) (Con’t)• The Test

– Dissolve one drop of liquid sample or 10 mg of solid sample in 1 mL pure Acetone

– Add 1 drop of Chromic Acid reagent

– Blue green color appears in less than 2 seconds for Primary and Secondary Alcohols

– Tertiary Alcohols do not produce blue-green color within 2 seconds and solution remains orange

04/17/2023 49

identifikasi analit

Documents

spot plate

spot teststest

unknown solution

thiocyanate spot test

na2co3 solution

kscn solution

na2so4 solution

ammonium molybdate solution