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Celebrates. National Chemistry Week. October 16-22. Stamp out. TELL ‘EM. Chemophobia. U CHEMISTRY. This message is approved by the USB Department of Chemistry. IDENTIFICATION OF HOUSEHOLD CHEMICALS. TEST EXERCISE – 105 Points. A PUZZLE. OBJECTIVES.

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slide2

Celebrates

National Chemistry Week

October 16-22

slide3

Stamp out

TELL ‘EM

Chemophobia

U CHEMISTRY

This message is approved by the USB Department of Chemistry

identification of household chemicals

IDENTIFICATION OF HOUSEHOLD CHEMICALS

TEST EXERCISE – 105 Points

A PUZZLE

slide5

OBJECTIVES

YOU determineand describe 7 properties of a substance sufficiently accurately to permit:

other investigators to tell if they have

the same substance from their determination of the same properties

YOU, with those other investigators,

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

Confirm the identityof the substance through an additional confirmatory test

slide6

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
    • VinegarWater
    • Your Results Your Unknown
    • Oxidation / Reduction
slide7

Techniques:

Solubility determination Reporting Observations

Branched Procedures

Apparatus:

Test Tubes pH Paper

Bunsen Burner Melting Point Apparatus

Stirring Rod

slide8

WHAT ARE THE SEVEN TESTS?

  • 4 Solubility / Reactivity tests
    • 1. Solubility in / Reactivity with Water
    • 2. " Ammonia
    • 3. " Vinegar
    • 4. " Rubbing alcohol
  • 3 other tests
    • 5. pH of aqueous solution of unknown
    • 6. Reactivity with tincture of iodine
    • 7. Behavior at high temperature

Soluble: Forming a homogeneous liquid phase with 2 or more components (called a solution).

chemical pix
Chemical Pix

The Solvents

NH3 (aq)

Rubbing Alcohol

Vinegar

Ammonia

CH3 COOH(aq)

(CH3)2CHOH

H2O

Water

slide10

SOLUBILITY / REACTIVITY TESTS

  • Why these four solvents?
  • Water - The most common terrestrial solvent
  • (Extensive data on solubility in water exist,
  • but hydrogen bonding makes it a complex )
  • 2.Aqueous ammonia - A basic aqueous solvent
  • Likely to dissolve and react withacidic substances
  • 3. Vinegar (aqueous acetic acid) - An acidic aqueous solvent
  • Likely to dissolve and react withbasic
  • substances
  • 4. Rubbing alcohol (isopropanol) - A non-aqueous solvent
  • Likely to dissolve non-polar materials

Rule of Thumb:

Acids react with Bases & vice versa

slide11

HOW TO DO SOLUBILITY TESTS

Operational definition of solubility:

Solid is solublein solvent if ~20 mg

(1/4 spatulaful) or more dissolves in 2mL of

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

Use

small

test tubes

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

using a thin glass rod

Soluble: Forming a homogeneous liquid phase with 2 or more components (called a solution).

Requires Patience!

slide12

How much is 20 mg?

¼ spatulaful

2 mL

slide13

OTHER TESTS

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

Looking for evidence of REACTION, -

i.e., color change, - not solubility

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

Such substances are reducingagents

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

OPERATIONALLY,

you are asked to determine whether or not an aqueous solution of a substance bleaches tincture of iodine. If it does,

it is a reducing agent.

bleaches

I2 (alcohol) + 2e- 2I-

colorless

brown

Reducing agents give up electrons:

R R+ + e-

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

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

slide14

2. pH of aqueous solution

      • Looking for [acidic / neutral / basic] property of
      • aqueous solution of unknown.
      • 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!

One piece of pH paper can be used for multiple determinations. Please use it efficiently!

Stirring rod

pH = 8

pH paper

slide15

3. Behavior at elevated temperature

  • Heat solid sample in small test tube over
  • Bunsen flame ( In hood )
    • Point test tube away from anyone!
    • Observe any and all changes:
  • Melting
  • Sublimation (Solid to vapor with no melting)
  • Water condensing at top of tube
  • Bubbling, Gas evolution (smell, etc.)
  • Color change
  • Charring, etc.

As you complete each test, post your results

(in summary form) on table at front of laboratory

each student must perform report all 7 tests on his her unknown and an authentic sample
Each student must perform & report all 7 tests on his/her unknown and anauthentic sample
  • True
  • False
slide17

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

results of the confirmatory test on

both the unknown & authentic sample

slide18

SECTION 3-A

Post results AS YOU GET THEM. Other students are waiting for your results.

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

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

S = SOLUBLE (SS = SLIGHTLY SOLUBLE)

I = INSOLUBLE C = COLOR CHANGE

G = GAS EVOLVED NR = NO REACTION

.............. OTHERS AS REQUIRED

slide19

Use collective results to deduce which students have the same substance

Will require consultationon details that are basis

for summary observations in table

May require collaborative repetition

of some tests, e.g., if all

observations except one agree

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

ALL MEMBERSOF YOUR GROUP

ARE CORRECTLY IDENTIFIED

Exchange unknown samples and repeat the test together

slide20

STEP 3: Determinetentative identityof unknown

    • Working as team, carry out measurements
    • that permit making tentative identification
    • of unknown.
  • HOW?
    • Compare results of 4 solubility and 3 other
    • tests from Part 1 on your unknown
    • with results of same tests on a
    • selected set of
  • authentic samples.

CaCO3

chemical pix1
Chemical Pix

The Unknowns

Aspirin

Acetyl Salicylic Acid

Urea

Organic acids are characterized by the following grouping of atoms:

K

Cream of Tartar

Potassium Hydrogen Tartrate

Vitamin C

Ascorbic Acid

chemical pix2
Chemical Pix

CaCO3

Limestone

Sour Salt

Citric Acid

Washing Soda

Na2CO3.10H2O

Na2S2O3·5H2O

Na2B4O7·10H2O

Hypo

Sodium Thiosulfate

Borax

Sodium Tetraborate

slide24

The 9 Unknowns – Critical Properties

LimestoneCO3= + Ca+ (Base)

Washing SodaCO3= + Na+ Base

HypoReducing Agent + Na

Cream of TartarWeakAcid + K

Aspirin Weak Acid

Ascorbic Acid Reducing Agent/Weak Acid

Sour Salt Weak Acid

Urea Weak Base

Borax Na + Base

slide25
Carbonates and bicarbonates, e. g. CaCO3, Na2CO3, etc., are expected to generate which gas upon the addition of vinegar.
  • O2
  • CO2
  • H2
  • N2
slide26

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

By generalization of the epic poem:

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

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

slide27

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.
slide28

However,

Consistency of test results is necessary,

but not sufficient!

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

but the sample is actually soluble,

BOTH results are incorrect!

YOUR RESULTS MUST BE CONSISTENT,

BUT THEY ALSO MUST BE CORRECT!

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

slide29

Table of Solubilities in Water of Substances in SUSB-004

mg/mL

A well prepared student will check to see how the tabulated solubilities relate to the solubility criterion that we have defined (~10 mg/mL)

Acidic Hydrogens are indicated in Red

slide30

Look for properties that have high discrimination.

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 sameas unknown in a test

Limited evidence that they may be the same

Continue testing that known

E.g., Unknown dissolves in ammonia but

Authentic Sample X does not

slide32

Each group must perform and report all 7 tests on eachauthentic 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.

slide33

BUT:

  • You must report results of all 7 testson an authentic sample of your reported (un)known.

THEN -

slide34

STEP 4 – Confirmation

    • Aftertentative identification,

confirm hypothesis with one additional comparative measurement,

  • This is confirmation for:
    • ASPIRIN, UREA, ASCORBIC ACID & SOUR SALT
  • 1. Melting point
  • For substances that showed clean melting behavior, melting point determinations are used. Measure and compare melting points of:
  • Unknown
  • Authentic sample

TA’s will demonstrate use

of Melting point apparatus

slide35

2. Flame test

    • Flame test confirms presence of
      • Alkali metal salts
        • Na – YELLOW K - VIOLET
      • Alkaline earth salts
        • Ca - BRICK RED

Confirmation for:

Limestone Washing Soda

Hypo Cream of Tartar Borax

slide36

TIME MANAGEMENT

FINAL EXERCISE

100 POINTS BASED ON:

1. Accuracy of identification

2. Quality and completeness of observations &

appropriateness of methods of identification and confirmation

Must report results of all 7 tests for

both unknown AND authentic sample

+

results of confirmation test for

both unknown AND authentic sample

Exercise involves many potential operations.

Grade will reflect ability to

Organize activities, AND

Do only those which are necessary

slide37

What the well organized student will do

  • Begin working immediately when you get to lab.
  • 1. Assemble required apparatus
    • Test tube block,
    • 6 clean SMALL test tubes,
    • Test tube holder
    • Label tubes or block
  • Once you get your unknown,
  • 2. Prepare five samples of unknown
    • Place samples in test tubes
slide38

3. Perform tests

    • Solubilility in H2O, NH3, acetic acid, alcohol, pH test, I2 test, Heat test
    • Measure 2 mL with cylinder – once
    • use level in test tube for other samples
  • Reminder:Sample used to test for water solubility should also be used for:
  • pH measurement, AND
  • reaction with Tincture of I2

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

slide39

5. Find Partners

    • Look 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 samples
    • Look 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

a substance that bleaches tincture of iodine immediately is a n
A substance that bleaches tincture of Iodine immediately is a(n)
  • acid
  • base
  • oxidizing agent
  • reducing agent
slide41

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 solubility

Reaction has occurred if mixing with an aqueous solution bleaches the I2color immediately

Such substances are reducingagents

bleaches

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

slide42

Part 1 – Data collection on unknown - must be done ALONE and WITHOUT CONSULTATION

Next Exercise

Synthesis of Vanillyl Alcohol from Vanillin

Read and do Pre-lab – SUSB-039