Decision Making
1. How can students systematically predict whether or not a solid Am n+Bn m will be soluble in water? A convenient approach is to apply the following steps in order, based upon the two ions composing the solid, stopping at the step in which one of the ions first appears.
On the basis of the above rules, classify the following salts as soluble (S) or insoluble (I).
For more on the solubility rules, see Solubility and Precipitation module.
2. The fluorides, carbonates, and phosphates of all of the alkali metal ions except lithium are soluble in water. Explain lithium's unique solubility properties. [The crystal lattice energies are larger because of the small size of the lithium ion. See the item on solubility in the Common Student Misconceptions section.]
3. Sodium chloride is typically used on roads in the northeast in winter time to help to melt ice and snow. Unfortunately, the runoff from these roads is a very concentrated salt solution that kills plants growing alongside the road. Students may discuss the pros and cons of this application of salt. Could other compounds be used instead (magnesium chloride, for example)? [Select salts that provide nutrients needed for plant growth, such as NH4NO3, (NH4)2SO4, etc.] Students can research and explain to the class the phenomena which account for this process. [Freezing point depression and cell plasmolysis.]
Other Interest Items
1. Sodium is one of the least expensive of all metals. One pound of sodium costs only about 15 cents when purchased in large quantities.
2. It is estimated that there are only 15 g of the element francium in the top kilometer of the lithosphere.
3. An alloy composed of 12% sodium, 47% potassium and 41% cesium has a melting point of 78 °C, lower than any other known alloy. Imagine a metal made of three alkali metals which melts at a temperature far below room temperature!
As a consequence of their chemical reactivity, alkali metals are not found free in nature. Their preparation awaited the invention of the voltaic pile (battery) by Alessandro Volta in 1799, which provided a technology for adding electrons to the M+ ions to produce the metals. Another factor in the date of discovery is related to the rank order and mass percent abundance of these elements as ionic compounds in the lithosphere (earthÕs crust). The rank order and abundances are: Li, 27 (0.0065%); Na, 6 (2.74%); K, 7 (2.47%); Rb, 19 (0.028%); and Cs, 52 (0.00032%). Humphry Davy, in 1807, at the age of 29, prepared metallic potassium by the electrolysis of molten caustic potash (KOH); a few days later he prepared sodium from molten caustic soda (NaOH).
While serving as a laboratory assistant with the famous Swedish chemist, Jons Jacob Berzelius, J. A. Arfvedson in 1817 observed that lithium compounds had properties that were similar to those of sodium and potassium, except for the lower solubilities of the hydroxide and carbonate. Lithium, as an aqueous ion, was isolated by Arfvedson from petalite (LiAlSi4 O10), spodumene (LiAl(SiO3)2, and lepidolite (K2Li3Al4Si 7 O21 (OH,F)3). Davy recognized the plant origin of potassium from impure potassium carbonate in wood ashes or Òpot ashesÓ with the symbol for potassium, K, coming from the Latin equivalent, kalium. Sodium relates to the plant origin of soda ash with natrium, the Latin equivalent, giving the symbol Na. Lithium was chosen by Arfvedson to indicate its origin from stones (Greek, lithos). In 1818, Davy prepared metallic lithium by the electrolysis of molten Li2O.
Robert Bunsen and Gustav Kirchhoff, using the spectroscope they invented in 1859, discovered two of the alkali metals. In 1860, during a spectroscopic investigation of the brine mineral waters in a spa in Durkheim, they observed two bright double blue lines. The name cesium derives from the Latin caesius, meaning sky blue. A few months later they viewed the spectrum of a solution obtained by the chemical treatment of lepidolite and noted ruby-red lines. The Latin rubidus, meaning "deepest red," gave rise to the name, rubidium. In 1934, Marguerite Perey, a French radiochemist, identified element 87 as a decay product of actinium-227, which in turn ultimately comes from uranium-235. In honor of her native country she named the element francium.
Davy, widely known for his invention of the safety lamp, described his discovery of potassium as follows:
A small piece of pure [caustic] potash [KOH] which had been exposed for a few seconds to the atmosphere, so as to give conducting power to the surface [by attraction of moisture and slight deliquescence], was placed upon an insulated disc of platina [platinum], connected with the negative side of the battery in a state of intense activity; and a platina wire, communicating with the positive side, was brought in contact with the upper surface of the alkali. The potash began to fuse at both its points of electrization. There was a violent effervescence at the upper surface; at the lower, or negative surface, there was no liberation of elastic fluid, but small globules having a high metallic lustre, and being precisely similar in visible characters to quicksilver [mercury], appeared, some of which burnt with explosion and bright flame, as soon as they were formed, and others remained, and were merely tarnished, and finally covered with a white film that formed on their surfaces. These globules, numerous experiments soon showed to be the substance I was in search of, and a peculiar inflammable principle the basis of potash.
Davy named the new element potassium and then by further experiments prepared sodium, calcium, barium, strontium, and magnesium by electrolysis.
Pliny in his writings mentions that the Egyptians made caustic soda [NaOH] by boiling natron [Na2CO3] with quicklime [CaO]. Duhamel (1736) and A. Marggraf (1757) showed that potash [K2CO3] from wood ashes and soda [Na2CO3] from the ashes of marine plants could be distinguished by two tests:
1. Heat on platinum wire: potash gives lilac flame; soda gives a yellow flame.
2. Add platinic chloride to a solution in HCl: potash gives yellow precipitate; soda forms no precipitate. The Hebrews knew that vinegar effervesced with natural sodium carbonate.
In Proverbs 25:20, ". . . like vinegar poured on soda is one who sings songs to a heavy heart." Gunpowder was made by the Chinese in about 1150 A.D.for use in making fireworks. This mixture of 75 parts KNO3 , 13 parts carbon, and 12 parts sulfur by mass was reinvented in the western world by Roger Bacon in about 1248 A.D.
Gay-Lussac and Thénard (1808) showed that molten caustic potash (KOH) or caustic soda (NaOH) brought into contact with red-hot iron turnings produced the respective alkali metal as a distillate.
Castner (1886) produced sodium on a large scale by heating NaOH with iron and carbon at a temperature of 1000 °C:
By 1890, Castner developed a large scale electrolytic method for preparing sodium using a cylindrical iron pot with an iron cathode and a nickel anode.
Joseph Black (1728-1799) in his book, Dissertation on Magnesia (1754), summarized his research on the chemical nature of the alkalies.
By the "principle of causticity" limestone absorbs phlogiston from the fire to produce caustic lime. Soon after this Black showed that in this process there was a loss of mass, and he revised his equation.
Words about the concepts in this module can be obtained from the clues given. Find these words in the block of letters:
1. Family of elements characterized by its vigorous reaction with water (2 words).
2. Negatively charged ion.
3. Positively charged ion.
4. Charge on an ion divided by its surface area (2 words).
5. Process by which compounds are decomposed electrically.
6. Family that is very reactive with alkali metals in which binary ionic compounds in a one-to-one ratio are formed.
7. Property of alkali metals that increases from Li+ to Fr+ (2 words).
8. Group of elements characterized by luster, malleability, ductility, and good electrical and heat conductivity.
9. Mineral deposit containing sufficiently high concentration to allow practical recovery of a metal.
10. Smallest part of a crystal that, if repeated, could generate the whole crystal (2 words).
Answers: 1. ALKALI METALS 2. ANION 3. CATION 4. CHARGE DENSITY 5. ELECTROLYSIS 6. HALOGENS 7. IONIC RADIUS 8. METALS 9. ORE 10. UNIT CELL
5. See cartoons at end of module.
1. "Chemical Families," videotape of a CHEMStudy film, distributed by Ward's Scientific Establishment, Inc., P.O. Box 92912, Rochester, NY 14692-9012, Telephone: (716) 359-2502, FAX: (716) 334-6174. Excellent film showing chemical reactions of the alkali metals and lots of other elements. Shows the relationships within families in the Periodic Table. Also available from the same company as a 16 mm film. 2. "The Great Sodium Disaster," by Clifford Schrader. A homemade video of several 1- and 5-pound chunks of sodium and potassium being tossed into an abandoned mine pit. Some great, and some not-so-gre
at photography and sound. Distributed by Weird Science, c/o L. Marek, Naperville High School, Naperville, IL. 3. "Databases in the Classroom: AppleWorks Sampler," 1986 Minnesota Educational Computer Consortium, St. Paul, MN 55165. The program contains a database of ÒThe Elements of the Periodic Table,"fully compatible with AppleWorksÑvery useful to organize large amounts of data by sorting and arranging into meaningful patterns.
4. "MECC Database Sampler," 1985 Minnesota Educational Computer Consortium, St. Paul, MN 55165. This program uses a rudimentary database developed by MECC, called DATAQUEST. It has much of the same data as the AppleWorks Sampler above, but much less ability to manipulate (sort or arrange data). This program may be more available than the AppleWorks Sampler above, since it is part of (and therefore free with) the MECC School Site Licensing Agreement Program, in which many schools nationwide participate. The AppleWorks Sample disk and documentation is sold separately and is not free with the licensing program.
5. "Periodic TableWorks," JCE Software, August 1988. This program is a publication of the Journal of Chemical Education, available from the Project SERAPHIM, Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, WI 53706. According to the brochure, this program "converts Apple II computer into an electronic Periodic Table. It highlights elements, groups, or periods; it then displays states, data, or trends of selected properties." It does what it says! It works great for periodicity and trends.
6. "Chemical Families," a CHEM Study film, distributed by Ward's Natural Scientific Establishment. Excellent film showing chemical reactions of the alkali metals and other elements. Shows the relationships within families on the Periodic Table. Also available from the same company as a videotape (VHS).
7. "The Periodic Table" BBC Productions for the Open University, distributed by the Media Guild, 11722 Sorrento Valley Road, Suite E, San Diego, CA 92121-1021. Phone: (619) 755-9191. The film shows good reaction sequences of the alkali metals and halogens. It includes animation and humor.
8. "Alkali Metal Reactions with Chlorine and with Water" Modern Learning Aids CHEM Study Series 092 #4004 This filmloop contains the same close-up sequences as the Chemical Families film. Its advantage over the film is that you can stop the loop to ask questions or slow it down to see frame by frame (almost). Its disadvantage is that you must explain what students are seeing, as there is no sound.
9. "Physical Properties of the Alkali Metals" Fitch, R. M., and J. T. Fitch, Harper and Row Publishers 04-94872, Harper & Row Publisher, Inc., Keystone Industrial Park, Seranton, PA 18512, FAX: (717) 343-3611. "10. "Chemical Properties of the Alkali Metals" Fitch, R. M., and J. T. Fitch, Harper and Row Publishers 04-94914.
11. "Formation by Electrolysis" Fitch, R. M., and J. T. Fitch, Harper and Row Publishers 04-94455.
12. Software published by JCE: Software, a publication of the Journal of Chemical Education, Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue. Madison, Wl 53706-1396: (608) 262-5153 (voice) or (608) 262-0381 (FAX).
a. KC? Discoverer with Knowledgeable Counselor, by Daniel Cabrol, John W. Moore and Robert C. Rittenhouse. Special Issue 2, for IBM PS/2, PC compatible computers.
b. KC? Discoverer: Exploring the Properties of the Chemical Elements, by Aw Feng and John W. Moore. Vol. I B, No. 1, for IBM PS/2, PC compatible computers.
c. KC? Discoverer?, by Michael Liebl, Vol. IV A, No. 2, for all Apple II computers.
d. The Periodic Table Stack, by Michael Farris. Vol. I C, No. 1, for the Apple Macintosh.
e. The Periodic Table (ToolBook), by Paul F. Schatz, John C. Kotz and John W. Moore, in press, for Windows running on IBM PS/2 PC-compatible computers.
13. Software published by Project SERAPHIM, Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue. Madison, WI 53706-1396; (608) 263-2837 (voice) or (608) 262-0381 (FAX). For the Apple II computer: AP 207
14. Videodiscs published byJCE: Software, a publication of the Journal of Chemical Education, Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue. Madison, Wl 53706-1396: (60) 262-5153 (voice) or (608) 262-0381 (FAX).
a. "Similarities and Trends in Groups II Alkali Metals," a chapter on the videodisc Demonstrations in Organic Chemistry (double sided, 60 min.), Special Issue 6.
b. The Periodic Table Videodisc (single side, 30 min.). Special Issue 1.
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