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IDENTIFICATION OF IDENTIFICATION OF HOUSEHOLD HOUSEHOLD CHEMICALSCHEMICALS

TEST EXERCISE – 105 Points

A PUZZLE

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Environmental Health and Safety has surveyed the Introductory Laboratories.

We have been advised that campus policy now requires that:

Students wear clothing in laboratory that leaves NO skin exposed below the waist.

This regulation will be rigorously enforced.

YOU determindetermine and describedescribe 7 properties of a substance sufficiently accurately to permit:

OBJECTIVESOBJECTIVES

YOU, with those other investigators,

other investigators to tell if they have the same substance same substance from their determination of the same properties

Infer the identityInfer the identity of the substance by comparison of its 7 properties with those of a list of 9 possible substances.

Confirm the identityConfirm the identity of the substance through an additional confirmatory testconfirmatory test

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Concepts:

Acid Ammonia

Base Confirmatory Test

Flame Test High Temperature Behavior

Isopropanol Known Substance Results

Known Substances Melting Point

Other’s Unknowns Other’s Results

Partners pH of Aqueous Solution

Posted Reaction with Iodine

Solubility Tests

Vinegar Water

Your Results Your Unknown

Oxidation / Reduction 5

Techniques:

Solubility determination Reporting Observations

Branched Procedures

Apparatus:

Test Tubes pH Paper

Bunsen Burner Melting Point Apparatus

Stirring Rod

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4 Solubility / Reactivity tests1. Solubility in / Reactivity with Water2. " Ammonia3. " Vinegar4. " Rubbing

alcohol

3 other tests5. pH of aqueous solution of unknown6. Reactivity with tincture of iodine7. Behavior at high temperature

WHAT ARE THE SEVEN TESTS?WHAT ARE THE SEVEN TESTS?

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Soluble: Forming a Soluble: Forming a homogeneous liquid phase homogeneous liquid phase with 2 or more components with 2 or more components

(called a solution).(called a solution).

Chemical Pix

The SolventsThe Solvents

Vinegar Ammonia

Water

Rubbing Alcohol

H2O

NH3 (aq)

CH3 COOH

(aq) (CH3)2CHOH

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Why these four solvents?1.Water - The most common terrestrial solvent

(Extensive data on solubility in water exist,but hydrogen bonding makes it complex )

2.Aqueous ammonia - A basic aqueous solventLikely to dissolve and react with acidic

substances

3. Vinegar (aqueous acetic acid) - An acidic aqueous solvent

Likely to dissolve and react with basic substances

4. Rubbing alcohol (isopropanol) - A non-aqueous solvent

Likely to dissolve non-polar materials

SOLUBILITY / REACTIVITY TESTSSOLUBILITY / REACTIVITY TESTS

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Rule of Thumb:Rule of Thumb:Acids react with Acids react with

Bases & vice Bases & vice versaversa

test tubes

HOW TO DO SOLUBILITY TESTSHOW TO DO SOLUBILITY TESTS

Operational definition of Operational definition of solubilitysolubility::

Solid is soluble in solvent if ~20 mg20 mg (1/4 spatulaful) or more dissolves in 22 mLmL of

solvent ( 0.01g/1.00g = 1% solution ) @ ~20~20ooCC

Requires Patience!

Solubility can be accelerated by tapping test tube, or stirring (using a thin glass rod)

Use small

using a thinthin glass rod

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Soluble: Forming a Soluble: Forming a homogeneous liquid phase homogeneous liquid phase with 2 or more components with 2 or more components

(called a solution).(called a solution).

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How much is 20 mg?How much is 20 mg?

¼ ¼ spatulafulspatulaful

2 2 mLmL

1. Behavior with tincture of Iodine: (I2 in alcohol)Looking for evidence of REACTION, -

i.e., color change, - not solubilitynot solubilityReaction has occurred if mixing with an aqueous

solution bleaches the I2 colorSuch substances are reducingreducing agentsagents

OTHER TESTSOTHER TESTS

I2 (alcohol) + 2e- 2I-

brown colorless

Reducing agents give up electrons:

R R+ + e-

e.g., vitamin C (ascorbic acid) , e.g., vitamin C (ascorbic acid) , hypohypo

bleachbleacheses

Whether or not you have studied oxidation and reduction in detail,

OPERATIONALLYOPERATIONALLY,

you are asked to determine whether or not an aqueous solution of a substance

bleaches tincture of iodine. If it does so, instantly,

it is a reducing agent.reducing agent.

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Note: Strongly basic solutions also bleach Note: Strongly basic solutions also bleach iodine solutions, but this occurs slowly.iodine solutions, but this occurs slowly.

2. pH of aqueous solution• Looking for [acidic / neutral / basic] property of

aqueousaqueous solution of unknown. • DO NOT make new aqueous solution!DO NOT make new aqueous solution!• Transfer drop of aqueous solution to piece of

pH paper using clean stirring rod • Observe color change.• Compare with colors on pH paper container

(posted in lab)Record and post value!Stirring

rod

pH pape

r

pH = 8

One piece of pH paper can be used

for multiple determinations.

Please use it efficiently!

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3. Behavior at elevated temperatureHeat solid sample in small test tube over Bunsen flame ( In hood )

Point test tube away from anyone! Observe any and all changes:

MeltingSublimation (Solid to vapor with no melting)Water condensing at top of tubeBubbling, Gas evolution (smell, etc.)Color changeCharring, etc.

As you complete each test, post your results (in summary form) on table at front of laboratory

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Each student must perform & report all 7 tests on his/her unknown and an

authentic sample

A. B.

0%0%

A. TrueB. False

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Each student must perform & report all 7 tests on his/her unknown and an

authentic sample

A = True

AND, in addition,you must report the AND, in addition,you must report the results of the results of the confirmatory test confirmatory test on on

both the unknown & authentic sampleboth the unknown & authentic sample

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SECTION 3-A

UnknID

Sol. in

water

Sol. in

ammon

Sol. in

vineg

Sol. in

rub alc

pH of water

sol

Behav with

tinc of Iodine

Behav under

heating

Miller A76 S S G S 10 NR G

Smith A33 I I I S ? C MELT

Baker A15 S S S I 4 NR MELT

Starr A56 S S G S 9 NR G

.....................

.....................

Simon A68 S S I I 5 C NR

S = SOLUBLE (SS = SLIGHTLY SOLUBLE)I = INSOLUBLE C = COLOR CHANGEG = GAS EVOLVED NR = NO REACTION.............. OTHERS AS REQUIRED

Post results AS YOU Post results AS YOU GET THEM. Other GET THEM. Other

students are waiting students are waiting for your results.for your results.

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Use collective results to deduce which students have the same substance

Will require consultation on details that are basis

for summary observations in table May require collaborative repetition

of some tests, e.g., if all observations except one agreeUnkn

IDSol.

inwater

Sol. in

ammon

Sol. in

vineg

Sol. in

rub alc

pH of water

sol

Behav with

tinc of Iodine

Behav under

heating

Miller A76 S S G S 10 NR G

Starr A56 S S G S 9 BLCH G

Exchange unknown samples and repeat the test Exchange unknown samples and repeat the test togethertogether

DO NOT PROCEED WITH IDENTIFICATION AND CONFIRMATION OF UNKNOWN UNTIL TA HAS

VERIFIED THAT ALLALL MEMBERS OF YOUR GROUP ARE CORRECTLY IDENTIFIED

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STEP 3: Determine tentative identity of unknown

Working as team, carry out measurements that permit making tentative identificationtentative identification of unknown.

HOW?CompareCompare results of 4 solubility and 3 other tests from Part 1 on your unknownunknown with results of same tests on a selected setselected set of

CaCO3

authentic authentic samplessamples.

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A Concept Map for this ExerciseA Concept Map for this Exercise

Chemical Pix

Urea AspirinAcetyl Salicylic

Acid

Cream of TartarPotassium Hydrogen Tartrate

Vitamin CAscorbic

Acid

HC

HCCH

CH

CC

CO OH

OC

O

CH3

CH

C

C C

O

CH

H2CHO OH

HO O

HO

H2NC

NH2

O

C

CH

CHC

HO O

O

OH

HO

HO

The The UnknownsUnknowns

K

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Organic acids are characterized by the following grouping of atoms:

COH

O

Chemical Pix

HypoSodium

Thiosulfate

Limestone

BoraxSodium

Tetraborate

Washing Soda

Sour SaltCitric Acid

CH2

C

CH2

C

OH

O

OH

O

HO

OH

O CaCO3

Na2S2O3·5H2

O Na2B4O7·10H2

O

Na2CO3.10H2

O

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LimestoneLimestone COCO33== + CaCa + (Base)Base)

Washing SodaWashing Soda COCO33== + NaNa + BaseBase

HypoHypo Reducing AgentReducing Agent + NaNa

Cream of TartarCream of Tartar WeakWeak AcidAcid + KK

AspirinAspirin Weak Weak AcidAcid

Ascorbic AcidAscorbic Acid Reducing Agent/Weak Reducing Agent/Weak AcidAcid

Sour SaltSour Salt Weak Weak AcidAcid

UreaUrea Weak Weak BaseBase

BoraxBorax NaNa + + BaseBase

The 9 Unknowns – Critical The 9 Unknowns – Critical PropertiesProperties

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Carbonates and bicarbonates, e. g. CaCO3, Na2CO3, etc., are expected to

generate which gas upon the addition of vinegar.

A. B. C. D.

0% 0%0%0%

A. O2

B. CO2

C. H2

D. N2

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Johnny finding life a bore, Drank some H2SO4

Johnny's father, an M.D., Gave him CaCO3

Now Johnny's neutralized its true,But he's also full of CO2

On what basis are you expected to know the answer to this question?

By generalization of the epic poem:

(And now, on the basis of this (And now, on the basis of this lecture!)lecture!)

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Do you have to do 7 X 9 = 63 Tests?

Not if you approach this step logically and use common sense.

Analyze the results of the 7 tests from Part 1 e.g., IF - your unknown appears to be an acid

i.e., dissolves in and reacts with NH3, aqueous solution has low pH,

THEN - Start tests with known substances that are acids. 26

However,

Consistency of test results is necessarynecessary, but not sufficientsufficient!

E.g., if you claim the sample is NOT SOLUBLE in water and, therefore, do NOT perform the pH test,

BOTH results are incorrectincorrect!

YOUR RESULTS MUST BE CONSISTENTCONSISTENT, BUT THEY ALSO MUST BE CORRECTCORRECT!

A table of solubilities in water of the substances in this exercise is posted on the Web

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but the sample is actually soluble,

Table of Solubilities in Water of Substances in SUSB-004

Common Name Chemical Name Formula Solubility

(g/100mL H2O)

@ 20oC

Washing Soda Sodium carbonate Na2CO3 50 (500)

Limestone Calcium carbonate CaCO3 0.0013 (0.013)

Vitamin C Ascorbic Acid HC6H7O5 100 (1000)

Hypo Sodium Thiosulfate (pentahydrate)

Na2S2O3 .5H2O 70 (700)

Cream of Tartar Potassium Hydrogen Tartrate KHC4O4H5 0.5 (5)

Aspirin Acetyl salicylic acid HC9H7O4 0.33 (3.3)

Urea Urea CH4N2O 100 (1000)

Sour Salt Citric acid H3C9H5O4 59 (590)

Borax Sodium tetraborate (decahydrate)

Na2B4O7 .10H2O 6 (60)

Acidic Hydrogens are indicated in Red

A well prepared student will check to see how the

tabulated solubilities relate to the solubility criterion that we

have defined (~10 mg/mL)

mg/mL

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I.e., those whose values vary most from substance to substance in posted table

If authentic sample behaves completely differently from unknown in any test

No reason to perform additional tests on

that authentic sample

If authentic behaves same as unknown in a test

Limited evidence that they may be the sameContinue testing that known

E.g., Unknown dissolves in ammonia but Authentic Sample X does not

Look for properties that have high discrimination.

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Each group must perform and report all 7 tests on each authentic sample.

A. B.

0%0%

A. TrueB. False

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Each group must perform and report all 7 tests on each authentic sample.

B = False

If tests are performed carefully & results are analyzed logically, number of tests

required to infer a presumed identity for unknown can be small.

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BUT:BUT:

THEN -

You must report results of all 7 testsall 7 tests

on an authentic authentic samplesample of your

reportedreported (un)known.

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STEP 4 STEP 4 – Confirmation– ConfirmationAfterAfter tentative identification,

1. Melting point1. Melting pointFor substances that showed clean melting behavior, melting point determinations are used. Measure and compare melting points of:

TA’s will demonstrate use of Melting point apparatus

UnknownAuthentic sample

This is confirmation This is confirmation for:for:

ASPIRINASPIRIN, , UREA, UREA, ASCORBIC ACID ASCORBIC ACID & SOUR SALT& SOUR SALT

confirm hypothesisconfirm hypothesis with one additional comparative measurement,

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2. Flame test

Flame test confirms presence of Alkali metal salts

Na – YELLOWYELLOW K - VIOLETVIOLET

Alkaline earth saltsCa - BRICK REDBRICK RED

Confirmation for:Confirmation for:LimestoneLimestone Washing Soda Washing SodaHypoHypo Cream of Tartar Cream of Tartar

BoraxBorax

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TIME MANAGEMENTTIME MANAGEMENTFINAL EXERCISE

100 POINTS BASED ON:1. Accuracy of identification 2. Quality and completeness of observations &

appropriateness of methods of identification and confirmation

+results of confirmation test forboth unknown AND authentic

sampleExercise involves many potential operations. Grade will reflect ability to

Organize activities, AND Do only those which are necessary

Must report results of all 7 tests forboth unknown AND authentic

sample

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What the well organized student will doWhat the well organized student will do

Begin working immediately when you get to lab.

1. Assemble required apparatusTest tube block, 6 clean SMALL test tubes,Test tube holder

Label tubes or block

Once you get your unknown,

2. Prepare five samples of unknownPlace samples in test tubes

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3. Perform tests

Solubilility in H2O, NH3, acetic acid, alcohol, pH test, I2 test, Heat test

Measure 2 mL with cylinder – onceuse level in test tube for other samples

Reminder: Sample used to test for water solubility should also be used for:

pH measurement, ANDreaction with Tincture of I2

4. Post results as you get them !!!!

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5. Find PartnersLook for individuals who have posted results that are closest to agreeing with your own.

Once you have found your (3) partners:

6. Do tests on authentic samplesLook for samples whose test results are closest to agreeing with your unknown.

Identify a tentative substance. (Be sure you have all 7 test results for that substance).

7. Do appropriate confirmatory test

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A substance that bleaches tincture of Iodine immediately is a(n)

A. B. C. D.

0% 0%0%0%

A. acidB. baseC. oxidizing agentD. reducing agent

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A substance that bleaches iodine solution is a(n):

D = Reducing Agent

1. Behavior with tincture of Iodine: (I2 in alcohol)

Looking for evidence of REACTION, - i.e., color change, - not solubilitynot solubility

Reaction has occurred if mixing with an aqueous solution bleaches the I2 color immediately

Such substances are reducingreducing agentsagents

bleachbleacheses

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Note: Strongly basic solutions also bleach Note: Strongly basic solutions also bleach iodine solutions, but this occurs slowly.iodine solutions, but this occurs slowly.

Next ExerciseNext Exercise

Synthesis of Vanillyl Alcohol from Vanillin

Read and do Pre-lab – SUSB-039

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