Presentation on theme: "Objective To identify the contents of fifteen different test tubes using a few simple tests and their mutual reactivities. Color – Transition metals tend."— Presentation transcript:
Objective To identify the contents of fifteen different test tubes using a few simple tests and their mutual reactivities. Color – Transition metals tend to form brightly colored compounds. pH – Using universal litmus paper determine the pH of the compound. Odor – Some compounds have very distinctive odors. When testing for odor always remember to WAFT! 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
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 +, Li +, Na +, K +, Ca 2+, Ba 2+, Fe 3+, Cu 2+, Ni 2+, Pb 2+ and Sn 2+. Anions – Negatively charged ions. Anions in today’s experiment include: Cl -, S 2-, NO 3 -, SCN -, SO 4 2-, CO 3 2-, CrO 4 2-, CH 3 CO 2 -, and C
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!
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) AgNO 3(aq) + NaCl (aq) NaNO 3(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)
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) + NO 3 -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) + NO 3 -1 (aq) + Na +1 (aq) + Cl -1 (aq) Na +1 (aq) + NO 3 -1 (aq) + AgCl (s) (Spectator Ions)
Test the pH of all solutions using Litmus paper. Tear the Litmus paper in half. Place pieces of Litmus paper on a watch glass, half off the edge of the glass. Place a drop of the solution on the portion of the paper over the glass. Pick up the paper from the side hanging off the glass. Compare the color of the paper to the chart on the side of the bottle. Record as whole numbers. Testing for pH The 3 High pH solutions will be NH 4 OH, Na 2 S, Li 2 CO 3 (Note: These will be the only ones with odor.) No odor – red flame - ? Smells like rotten eggs – yellow flame - ? Smells like cleaning solution – no flame change - ? The 3 Low pH solutions will be H 2 SO 4, SnCl 2, Fe(NO 3 ) 3 Orange solution - ? Reacts with Na 2 S to give a brown/black ppt - ? Reacts with Na 2 S to form bubbles - ? (Note: the bubbles may not be noticeable.)
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.
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
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
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 Red Te Tellurium - Pale green Tl Thallium - Pure green Zn Zinc - Bluish Green
And Now for the Main Event!
Mystery of the Fifteen 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 15 Test Tubes. Yeah, we know it’s cheesy !
The Usual Suspects 1.H 2 SO 4 2.K 2 CrO 4 3.Fe(NO 3 ) 3 4.Na 2 S 5.NiSO 4 6.KNO 3 7.Ba(NO 3 ) 2 8.NH 3 9.NaCl 10.K 2 C 2 O 4 11.Cu(NO 3 ) 2 12.SnCl 2 13.KSCN 14.Li 2 CO 3 15.Pb(CH 3 CO 2 ) 2
H 2 SO 4 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). Please open your book to page 118 & take notes in the margins.
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 H 2 SO 4 will char paper by dehydration if left in contact for a sufficient while. MSDS for H 2 SO 4
NH 3 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.
K 2 CrO 4 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.
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 CrO 4 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.
NaCl Sodium Chloride Bio: Nothing but a common salt, almost impossible to recognize in a crowd (unless accompanied by lead), but shows quite a yellow streak when the real heat is on.* *i.e., the flame test will yield a yellow flame.
Fe(NO 3 ) 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.)
K2C2O4K2C2O4 Bio: Actions not well known, but moderate toxicity noted, handle with care, believed to have a falling out with “Barium”. Potassium Oxalate
Na 2 S Sodium Sulfide Bio: Alias “Le Pew”, a real loner, possible messy confrontations with lead, 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?
Cu(NO 3 ) 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.
NiSO 4 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.
SnCl 2 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 3 M HCl, so it will appear quite acidic.
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· ə s ′s ə l′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.
KNO 3 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.”
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)
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.*
Ba(NO 3 ) 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.
Li 2 CO 3 Lithium Carbonate Bio: A white salt, sparingly soluble. Recall all carbonates, except Li, Na & K are insoluble. Lithium like her sisters sodium and potassium never reacts, but is easily inflamed. Turns bright red when the fireworks start! In the late 1800’s, some doctors recommended a therapy with lithium salts for a number of ailments, including gout, urinary calculi, rheumatism, mania, depression, and headache. In 1949, John Cade discovered the anti-manic effects of lithium ions. which led to lithium being used to treat bipolar disorder.
Pb(CH 3 CO 2 ) 2 Lead (II) Acetate Bio: Aside from lead nitrate the only soluble form of lead. Toxic. Turns green when inflamed. Has a sweet taste and has been used as a sugar substitute throughout history. The ancient Romans, who had few sweeteners besides honey, would boil grape juice in lead pots to produce a reduced sugar syrup called defrutum, concentrated again into sapa. It is no longer used as a sweetener though, because of its toxicity.
The NITRATES are a red herring. Which direction are they leading us?* Page Postlab Question #2 *Note: This question has nothing to do with blue babies…
1 Set of 16 Test Tubes in a Test Tube Rack - Return – Dump 15 Unknowns & HCl in waste container & rinse test tubes with distilled water. (Use distilled water bottle to rinse test tubes.) 15 Beral Pipettes – Discard 6 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. 1 Set of 16 Test Tubes in a Test Tube Rack – 15 Unknowns & HCl 15 Beral Pipettes 6 24-well wellplates 1 Nichrome Wire 1 Striker 1 Vial of pH paper
Midterm Exam (March 3-5) ~1 Hour Exam During first hour of regularly scheduled class. Midterm Review Wednesday, Feb. 25, 4:00-6:00pm in G3 Schrenk For March Read: Dilutions / Beer’s Law – Pages in the Lab Packet Good Luck! Due: 15 Test Tubes Packet , 215 & 217* and Textbook Postlab pages You are welcome to turn this handout in either the week of March or after the exam March 3-5 ( *The 15 Test Tubes 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.)