Mystery of the 13 Test Tubes - PowerPoint Presentation

Slide1

Mysteryof the13 Test Tubes

Slide2

Objective

To identify the contents of thirteen different test tubes using a few simple tests and their mutual reactivities.

Color

– Transition metals tend to form brightly colored compounds.Odor – Some compounds have very distinctive odors. When testing for odor always remember to

WAFT!

pH –

Using universal litmus paper determine the pH of

the compound.Solubility – By combining the unknowns and knowing the rules of solubility, one can determine the contents of the test tubes.Flame Test – Metal ions when introduced into a flame give a distinct emission spectrum. The color of the flame can help identify the unknown metal.

Simple Tests

Slide3

Definitions Applicable to Ionic Reactions

Ions –

Charged Species. Metals tend to form cations and nonmetals tend to form anions

. Ionic substances tend to dissolve readily in water to form solutions because they are charged particles that should electrostatically attract the corresponding end of the water dipole. However,

not all ionic substances are soluble in water

,

indicating that they do not have enough energy to break apart the ionic crystal.

Cations – Positively charged ions. Cations in today’s experiment include: H

+

, Na

+

, K

+

, Ca

2+

, Ba

2+

,

Fe

3+

, Cu

2+

, Ni

2+

, and Sn

2+

.

Anions –

Negatively charged ions.

Anions in today’s

experiment include:

Cl

-

, S

2-

, NO

3

-

, SCN

-

, SO

4

2-

,

CrO

4

2-

, and C

2

0

4

2-

.

Slide4

Soluble - The term soluble means that a substance dissolves.  An aqueous solution is soluble.  If one mixes two solutions together and no precipitate forms

, then only the ions are in solution.  Thus, there is no precipitation reaction. Note: Sometimes when two solutions are mixed together, a reaction can occur that does not

form a precipitate.  Usually when this type of reaction takes place, there is a marked color change when the product is formed or a large temperature change is observed.

Insoluble - The term insoluble means a substance

does

not

dissolve

.  Precipitate – A solid beneath a liquid.  If one mixes two solutions and a solid forms,

this is called

a precipitation reaction

.

Slide5

Solubility Rules

1. All nitrates, chlorates, and acetates of all metals are soluble.

Silver acetate is sparingly soluble.

2. All sodium, potassium, and ammonium salts are soluble.

3. All chlorides, bromides, and iodides are soluble

except

silver, lead (II), and mercury (I).

4. All sulfates are soluble

except

barium, calcium, strontium,

lead (II), and mercury (I).

5. Carbonates, phosphates, borates, sulfites, chromates, and

arsenates of sodium, potassium, and ammonium are soluble;

all others are

insoluble.

6. Sulfides of barium, calcium, magnesium, sodium, potassium,

and ammonium are soluble

; all others are

insoluble.

7. Hydroxides of sodium, potassium, and ammonium are soluble.

Hydroxides of barium and calcium are moderately soluble.

8. Everything else will be considered insoluble!

Slide6

Overall Equation – Shows reactants and products as undissociated, electrically neutral compounds.

Complete Ionic Equation – Shows the state of reactants and products as hydrated or other phases.

Ag

+1(aq)

+ NO

3

-1

(aq) + Na+1(aq) + Cl

-1

(aq)

Na

+1

(aq)

+ NO

3

-1

(aq)

+ AgCl

(s)

AgNO3(aq) + NaCl(aq) NaNO3(aq) + AgCl(s)

Ionic Equations & Precipitation Reactions

Net Ionic Equation

– Shows only the reactants and products that are directly involved in the reaction.

Ag

+1(aq) + Cl-1(aq) AgCl(s)

Slide7

Spectator Ions – Ions which are not directly involved in the net ionic equation are called spectator ions. In the previous equation, this would be the sodium and nitrate ions.

Ag

+1

(aq) + NO3-1(aq) + Na

+1

(aq)

+ Cl

-1(aq) Na+1(aq)

+ NO

3

-1

(aq)

+ AgCl

(s)

Ag

+1

(aq)

+ Cl

-1

(aq)

AgCl(s)

(Net Ionic Equation)

Ag

+1(aq) + NO3-1

(aq) + Na+1(aq) + Cl-1(aq) Na+1(aq) + NO3-1(aq) + AgCl (s)

(Spectator Ions)

Slide8

Flame Tests

The flame test is a procedure used in chemistry to detect the presence of certain

metal ions, based on each element's

characteristic emission spectrum. The color of flames in general also depends on temperature.

The flame test is

fast and easy to perform

, and does not require any equipment not usually found in a chemistry laboratory. However, the

range of detected elements is small

, and the test relies on the

subjective experience

of the experimenter rather than any objective measurements.

Slide9

Samples are usually held on a nichrome wire cleaned with hydrochloric acid to remove traces of previous analytes.

Glass Rod with Nichrome Wire

The test involves introducing a sample of the element or compound to a hot,

non-luminous (blue) bunsen flame

, and observing the color that results.

Flame Tests

Flame Test Calcium

Slide10

Sodium is a common component or contaminant in many compounds and its spectrum tends to dominate over others. Thus the color yellow overpowers the true color.

The test flame is often viewed through cobalt blue glass to filter out the yellow of sodium and allow for easier viewing of other metal ions.

Flame Tests

Sodium - Yellow

Potassium - Purple

Barium - Green

Slide11

Flame Tests

As Arsenic - Blue

B Boron - Bright Green *Ba Barium - Apple Green Ca Calcium - Brick Red Cs Cesium - Pale Violet

Cu(I) Copper(I) - Blue Cu(II) Copper(II) (non-halide) - Green *Cu(II) Copper(II) (halide) -

Blue-Green

*Fe Iron - Gold

In Indium - Blue

*K Potassium - Lilac Li Lithium – Carmine Red

Mg Magnesium - Brilliant white

Mn(II) Manganese(II) –

Yellowish green

Mo Molybdenum - Yellowish green

*Na Sodium - Intense Yellow

P Phosphorus - Pale bluish green

Pb Lead - Pale green

Rb Rubidium - Pale violet

Sb Antimony - Pale green

Se Selenium - Azure blue

Sr Strontium - Crimson RedTe Tellurium - Pale green Tl Thallium - Pure green Zn Zinc - Bluish Green

Slide12

Mysteryof the13 Test Tubes

And Now

for the

Main Event!

Slide13

Mystery of the Thirteen Test Tubes

It was a cold dark night and one of the TAs was preparing the solutions for this week’s experiment. The

TA had made a key for the unknowns

and placed the key on the lab bench in the stockroom before she went home for dinner.

While the TA was out, one of the stockroom workers decided to help clean the stockroom.

(They know how upset Dr. Bone gets when the stockroom is a mess!)

And – you know it – the stockroom worker threw away the key!

So now it is up to you to identify the contents of the 13 Test Tubes.

Yeah, we know it’s cheesy!

Slide14

The Usual Suspects

H

2

SO

4

K

2

CrO

4

Fe(NO

3

)

3

Na

2

S

NiSO

4

KNO

3

Ba(NO3)2NH3NaClK2C2O4Cu(NO3

)2SnCl2KSCN

Slide15

H2SO4

Bio:

Strong Acid, most powerful industrial chemical in the world, may produce insoluble sulfates if “metal”ed (meddled) with.*

Sulfuric Acid

*Recall #4 of our solubility rules:

All sulfates are soluble

except

barium

, calcium, strontium, lead (II), and mercury (I).

Slide16

Corrosive; highly exothermic reaction with water. Burns from sulfuric acid are potentially more serious than those of comparable strong acids (e.g. hydrochloric acid), as there is additional tissue damage due to dehydration

and particularly due to the heat liberated by the reaction with water; i.e. secondary thermal damage. The danger is greater with more concentrated preparations of sulfuric acid; however, even the "dilute" ~ 0.1 M H2

SO4 will char paper by dehydration if left in contact for a sufficient while.

MSDS for H

2

SO

4

Slide17

NH3

Ammonia

A gas with a characteristic pungent odor. Caustic and can cause serious health damage. Exposure to very high concentrations of gaseous ammonia can result in lung damage and death.

Bio:

Alias

Ammonium Hydroxide (NH

4

OH)

has done important work in homes, last known employment as fertilizer, can turn ugly on

any nosey detectives.

Slide18

K

2

CrO4

Potassium Chromate

Bio:

Best known for its

bright disposition

, potassium ion is almost inert, but the chromate may

drop out if faced with

silver, lead or

barium

. Remains bright even when it lays low.

Slide19

Potassium Chromate is very toxic and may be fatal if swallowed. It may also act as a carcinogen, and can create reproductive defects if inhaled or swallowed.

K

2

CrO4

It is also possible that it

may react explosively

with other reducing agents and flammable objects.

It is a

strong oxidizing agent

. It may react rapidly, or violently.

Slide20

NaCl

Sodium Chloride

Bio:

Nothing but a common salt, almost impossible to recognize in a crowd, but shows quite a yellow streak when the real heat is on.*

*i.e., the flame test will yield a yellow flame.

Slide21

Fe(NO3)3

Ferric Nitrate

Bio:

Alias “

Iron III

” – Ferric is more reactive than younger brother Ferrous; may be recognized by color if not confused with other species, can be definitively identified by “

Bloody

” encounter with greatest rival

Thiocyanate

.*

Ferric

Fe

3+

Ferrous

Fe

2+

(*More about that in the KSCN slide.)

Slide22

K2C2O4

Bio:

Actions not well known, but moderate toxicity noted, handle with care, believed to have a falling out with “Barium”.

Potassium Oxalate

Slide23

Na2S

Sodium Sulfide

Bio:

Alias “

Le Pew

”, a real loner, possible messy confrontations with

copper, ferric, nickel or tin

; tends to linger on the skin if touched.

(Do NOT Touch!)

Caution:

Na

2

S + H

2

SO

4

yields which smelly gas?

Slide24

Cu(NO3)2

Cupric Nitrate

Bio:

First name officially changed to “

Copper II

”; leading chemical citizen, many business ventures include electrical wire manufacturing and production of alloys, notably brass; in solution is easily recognizable by “

melancholy

” (sad or blue) disposition.

Note:

Once suspected of

conspiring with ammonia to impersonate blue ink.

Slide25

NiSO4

Nickel Sulfate

Caution:

Nickel salts are considered carcinogenic.

Bio:

Once very valuable, now net worth greatly reduced, “

Nick

” is easily recognized by his “

envious

” (green) nature.

Slide26

SnCl2

Stannous Chloride

Bio:

a.k.a. Tin Chloride, a hard worker, known since ancient times, currently employed in food packaging industry, recyclable; fluoride form prevents tooth decay; somewhat acidic personality;

unfortunate confrontation with “Le Pew”.

Note:

Stannous Chloride was

prepared in 1 M HCl, so it will

appear quite acidic.

Slide27

Solutions of tin ( II) chloride can also serve simply as a source of Sn 2+ ions, which can form other tin (II) compounds via precipitation reactions, for example brown (or black) tin (II) sulfide:

Unfortunate Confrontation

with “Le Pew”

SnCl

2

(aq) + Na

2

S(aq) → SnS(s) + 2 NaCl(aq)

stannous sulfide (′stan·əs ′səl′fīd) SnS

Dark crystals; insoluble in water, soluble (with decomposition) in concentrated hydrochloric acid; melts at 880°C; used as an analytical reagent and catalyst, and in bearing material.

Also known as tin monosulfide; tin protosulfide; tin sulfide.

Slide28

KNO3

Potassium Nitrate

Bio:

The “Most Boring” substance known outside of the noble gasses, chronically unemployed, does not participate

in chemical reactions but often “

watches

”.

Can be distinguished from the other “

common salt

” by its pale

violet response

to any “

trial by fire

.”

Slide29

While potassium nitrate may be boring in solution, the solid is a critical oxidizing component of black powder gunpowder. In the past it was also used for burning fuse technologies including slow matches. Potassium nitrate has been widely "harvested" since the Late Middle Ages and up through the 19th century from urine. LeConte described the process: Place stale urine in a container of straw hay and allow it to sour for many months, then wash the straw with water. The resulting liquid contained potassium nitrate. The process was completed by filtering the liquid through wood ashes and air-drying the resulting filtrate in the sun.

Its common names include saltpeter, American English saltpeter, & Nitrate of potash.

KNO

3 (aq)

KNO

3 (s)

Slide30

KSCN

Potassium Thiocyanate

Bio:

Poisonous little creature, approach with caution, longstanding “blood” feud with the Iron Brothers.

*Note:

It may appear black in the well, use a stirring rod to smear some on a piece of white paper to verify color.

KSCN

+

FeCl

3

Chemists are always trying to make mimics of the Chemicals found in nature. We can do this by

mixing Iron(III) compounds with Potassium Thiocyanate

. The Chemical we get is similar to the Iron-containing part of hemoglobin and is a

blood red color

.*

Slide31

Ba(NO3)2

Barium Nitrate

Bio:

Little known on this one, chance encounters with sulfuric acid

have often

“precipitated

” pale consequences.

Toxic by ingestion or inhalation. Symptoms of poisoning include tightness of muscles (especially in the face and neck), vomiting, diarrhea, abdominal pain, muscular tremors, anxiety, weakness, labored breathing, cardiac irregularity, and convulsions. Death may result from cardiac or respiratory failure, and usually occurs a few hours to a few days following exposure to the compound. Barium nitrate may also cause kidney damage.

Slide32

The NITRATES

are

a red herring.

Which

Direction?

Slide33

Mystery of the 13 Test TubesCheck Out

1 Set of 14 Test Tubes in a Test Tube Rack -

Return

– Dump 13 Unknowns &

HCl

in waste container

& rinse test tubes with distilled water.

(Use distilled water bottle to rinse test tubes.)

13

Beral

Pipettes –

Discard

3

24-well

wellplates

– Return

after dumping chemicals and rinsing.1 Nichrome Wire & 1 Striker – Return1 Vial of pH paper – Return vial & unused pH paper. Return vial even if all pH paper was used.After Lab

1 Set of 14 Test Tubes in a Test Tube Rack

– 13 Unknowns &

HCl

13 Beral Pipettes 3 24-well wellplates

1 Nichrome Wire1 Striker1 Vial of pH paper

Slide34

Midterm Exam (Feb. 20-23)

~1 Hour ExamDuring regularly scheduled class.Midterm ReviewWednesday, Feb. 15,

4:30-6:30pmin G3 Schrenk

For

February 27 – March 1

Read:

Gas Laws

–

pages

71-82

(i.e., Chapter

#7

in the Lab Packet / Green Book)

Good Luck!

Due:

13 Test Tubes (

pp

125-130)*

- You are welcome to turn in the lab either the week of Feb. 20-23 (after exam) or

Feb. 27–Mar. 1. (*This material will be on the midterm exam. In order to study for the exam you should answer the post lab questions prior to the exam.)