To identify the contents of thirteen different test tubes
using a few simple tests and their mutual reactivities.
Simple Tests
Color – Transition metals tend to form brightly colored
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.
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+, Ca2+, Ba2+,
Fe3+, Cu2+, Ni2+, and Sn2+.
Anions – Negatively charged ions. Anions in today’s
experiment include: Cl-, S2-, NO3-, SCN-, SO42-,
CrO42-, and C2042-.
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.
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!
Ionic Equations & Precipitation Reactions
Overall Equation – Shows reactants and products
as undissociated, electrically neutral compounds.
AgNO3(aq) + NaCl(aq)
NaNO3(aq) + AgCl(s)
Complete Ionic Equation – Shows the state of
reactants and products as hydrated or other
Ag+1(aq) + NO3-1(aq) + Na+1(aq) + Cl-1(aq)
Na+1(aq) + NO3-1(aq) + AgCl
Net Ionic Equation – Shows only the reactants
and products that are directly involved in the
Ag+1(aq) + Cl-1(aq)
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) + NO3-1(aq) + AgCl
Ag+1(aq) + NO3-1(aq) + Na+1(aq) + Cl-1(aq)
Na+1(aq) + NO3-1(aq) + AgCl
(Spectator Ions)
Ag+1(aq) + Cl-1(aq)
(Net Ionic Equation)
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.
Flame Tests
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 Test Calcium
Samples are usually held on
a nichrome wire cleaned with
hydrochloric acid to remove
traces of previous analytes.
Glass Rod with Nichrome Wire
Flame Tests
Potassium - Purple
Sodium - Yellow
Barium - Green
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
As Arsenic - Blue
Mg Magnesium - Brilliant white
B Boron - Bright Green
Mn(II) Manganese(II) –
*Ba Barium - Apple Green
Ca Calcium - Brick Red
Yellowish green
Mo Molybdenum - Yellowish green
Cs Cesium - Pale Violet
*Na Sodium - Intense Yellow
Cu(I) Copper(I) - Blue
P Phosphorus - Pale bluish green
Cu(II) Copper(II) (non-halide) -
Pb Lead - Pale green
*Cu(II) Copper(II) (halide) Blue-Green
*Fe Iron - Gold
In Indium - Blue
*K Potassium - Lilac
Li Lithium – Carmine Red
Rb Rubidium - Pale violet
Sb Antimony - Pale green
Se Selenium - Azure blue
Sr Strontium - Crimson Red
Te Tellurium - Pale green
Tl Thallium - Pure green
Zn Zinc - Bluish Green
And Now
for the
Main Event!
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.
The Usual Suspects
Bio: Strong Acid, most
powerful industrial chemical in
the world, may produce
insoluble sulfates if “metal”ed
(meddled) with.*
*Recall #4 of our solubility rules:
All sulfates are soluble except barium,
calcium, strontium, lead (II), and mercury (I).
Sulfuric Acid
MSDS for H2SO4
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 H2SO4
will char paper by dehydration if left in
contact for a sufficient while.
Ammonia NH3
Bio: Alias Ammonium Hydroxide (NH4OH) has
done important work in homes, last known
employment as fertilizer, can turn ugly on
any nosey detectives.
A gas with a characteristic
pungent odor. Caustic and
can cause serious health
damage. Exposure to very
gaseous ammonia can result
in lung damage and death.
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.
Potassium Chromate
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.
It is a strong oxidizing agent.
It may react rapidly, or violently.
It is also possible that it may react
explosively with other reducing
agents and flammable objects.
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.*
Sodium Chloride
*i.e., the flame test will
yield a yellow flame.
Fe 3+
Fe 2+
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
Ferric Nitrate
(*More about that in the KSCN slide.)
Potassium Oxalate
Bio: Actions not well known, but moderate
toxicity noted, handle with care, believed to
have a falling out with “Barium”.
Bio: Alias “Le Pew”, a
real loner, possible
messy confrontations
with copper, ferric,
nickel or tin; tends to
linger on the skin if
(Do NOT Touch!)
Sodium Sulfide
Caution: Na2S + H2SO4
yields which smelly gas?
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.
Cupric Nitrate
Note: Once suspected of conspiring
with ammonia to impersonate blue ink.
Bio: Once very valuable, now net worth greatly
reduced, “Nick” is easily recognized by his “envious”
(green) nature.
Nickel Sulfate
Caution: Nickel salts are
considered carcinogenic.
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.
Stannous Chloride
Unfortunate Confrontation
with “Le Pew”
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:
SnCl2(aq) + Na2S(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.
Bio: The “Most Boring” substance known
outside of the noble gasses, chronically
unemployed, does not participate in
chemical reactions but often “watches”.
Potassium Nitrate
Can be distinguished from the
other “common salt” by its pale
violet response to any “trial by
KNO3 (aq)
KNO3 (s)
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.
Bio: Poisonous little creature, approach
with caution, longstanding “blood” feud
with the Iron Brothers.
Potassium Thiocyanate
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.*
*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 + FeCl3
Bio: Little known on this one, chance
encounters with sulfuric acid have often
“precipitated” pale consequences.
Barium Nitrate
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.
a red herring.
1 Set of 14 Test Tubes in a Test Tube Rack
– 13 Unknowns & HCl
13 Beral Pipettes
3 24-well wellplates
1 Nichrome Wire
1 Striker
1 Vial of pH paper
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 – Return
1 Vial of pH paper – Return vial & unused pH paper.
Return vial even if all pH paper was used.
For February 27 – March 1
Read: Gas Laws – pages 71-82
(i.e., Chapter #7 in the Lab Packet / Green Book)
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.)
Midterm Exam (Feb. 20-23)
~1 Hour Exam
During regularly scheduled class.
Midterm Review
Wednesday, Feb. 15,
G3 Schrenk

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