ALUMINUM AND ITS COMPOUND

ALUMINUM AND ITS COMPOUND

Ø    Purpose
Learning the properties of aluminum metal and its compound

Ø    Basic Theory

            Aluminum is found in Row 2, Group 13 of the periodic table. The periodic table is a chart that shows how the chemical elements are related to each other. Elements in the same column usually have similar chemical properties. The first element in this group is boron. However, boron is very different from all other members of the family. Therefore, group 13 is known as the aluminum family.

            Aluminum is the third most abundant element in the Earth's crust, falling behind oxygen and silicon. It is the most abundant metal. It is somewhat surprising, then, that aluminum was not discovered until relatively late in human history. Aluminum occurs naturally only in compounds, never as a pure metal. Removing aluminum from its compounds is quite difficult. An inexpensive method for producing pure aluminum was not developed until 1886.

Symbol :Al

Atomic Number :13

Atomic mass 26.98154

Family : Group 13 (IIIA)

Pronunciation

            Today, aluminum is the most widely used metal in the world after iron. It is used in the manufacture of automobiles, packaging materials, electrical equipment, machinery, and building construction. Aluminum is also ideal for beer and soft drink cans and foil because it can be melted and reused, or recycled.

Discovery and naming

            Aluminum was named for one its most important compounds, alum. Alum is a compound of potassium, aluminum, sulfur, and oxygen. The chemical name is potassium aluminum sulfate, KAl(SO ₄ ) ₂ .

            No one is sure when alum was first used by humans. The ancient Greeks and Romans were familiar with the compound alum. It was mined in early Greece where it was sold to the Turks. The Turks used the compound to make a beautiful dye known as Turkey red. Records indicate that the Romans were using alum as early as the first century B.C.

            These early people used alum as an astringent and as a mordant. An astringent is a chemical that causes skin to pull together. Sprinkling alum over a cut causes the skin to close over the cut and start its healing. A mordant is used in dyeing cloth. Few natural dyes stick directly to cloth. A mordant bonds to the cloth and the dye bonds to the mordant.

            Over time, chemists gradually began to realize that alum might contain a new element. In the mid-1700s, German chemist Andreas Sigismund Marggraf (1709-82) claimed to have found a new "earth" called alumina in alum. But he was unable to remove a pure metal from alum.

            The first person to accomplish that task was Danish chemist and physicist Hans Christian Oersted (1777-1851). Oersted heated a combination of alumina and potassium amalgam. An amalgam is an alloy of a metal and mercury. In this reaction, Oersted produced an aluminum amalgam—aluminum metal in combination with mercury. He was unable, however, to separate the aluminum from the mercury.

Today, aluminum is the most widely used metal in the world after iron.

            Pure aluminum metal was finally produced in 1827 by German chemist Friedrich Wöhler (1800-82). Wöhler used a method perfected by English chemist Sir Humphry Davy (1778-1829), who succeeded in isolating several elements during his life-time. (See sidebar on Davy in the calcium entry.) Wöhler heated a mixture of aluminum chloride and potassium metal. Being more active, the potassium replaces the aluminum, as shown by the following:

            The pure aluminum can then be collected as a gray powder, which must be melted to produce the shiny aluminum that is most familiar to consumers.

            After Wöhler's work, it was possible, but very expensive, to produce pure aluminum. It cost so much that there were almost no commercial uses for it.

            A number of chemists realized how important it was to find a less expensive way to prepare aluminum. In 1883, Russian chemist V. A. Tyurin found a less expensive way to produce pure aluminum. He passed an electric current through a molten (melted) mixture of cryolite and sodium chloride (ordinary table salt). Cryolite is sodium aluminum fluoride (Na ₃ AlF ₆ ). Over the next few years, similar methods for isolating aluminum were developed by other chemists in Europe.

            The most dramatic breakthrough in aluminum research was made by a college student in the United States. Charles Martin Hall (1863-1914) was a

student at Oberlin College in Oberlin, Ohio, when he became interested in the problem of producing aluminum. Using homemade equipment in a woodshed behind his home, he achieved success by passing an electric current through a molten mixture of cryolite and aluminum oxide (Al ₂ O ₃ ).

            Hall's method was far cheaper than any previous method. After his discovery, the price of aluminum fell from about $20/kg ($10/lb) to less than $1/kg (about $.40/lb). Hall's research changed aluminum from a semi-precious metal to one that could be used for many everyday products.

What's in a name?

            In North America, aluminum is spelled with one i and is pronounced uh-LOO-min-um. Elsewhere in the world, a second i is added—making it aluminium—and the word is pronounced al-yoo-MIN-ee-um.

Physical properties

            Aluminum is a silver-like metal with a slightly bluish tint. It has a melting point of 660°C (1,220°F) and a boiling point of 2,327-2,450°C (4,221-4,442°F). The density is 2.708 grams per cubic centimeter. Aluminum is both ductile and malleable. Ductile means capable of being pulled into thin wires. Malleable means capable of being hammered into thin sheets.

            Aluminum is an excellent conductor of electricity. Silver and copper are better conductors than aluminum but are much more expensive. Engineers are looking for ways to use aluminum more often in electrical equipment because of its lower costs.

Chemical properties

            Aluminum has one interesting and very useful property. In moist air, it combines slowly with oxygen to form aluminum oxide:

            The aluminum oxide forms a very thin, whitish coating on the aluminum metal. The coating prevents the metal from reacting further with oxygen and protects the metal from further corrosion (rusting). It is easy to see the aluminum oxide on aluminum outdoor furniture and unpainted house siding.

            Aluminum is a fairly active metal. It reacts with many hot acids. It also reacts with alkalis. An alkali is a chemical with properties opposite those of an acid. Sodium hydroxide (common lye) and limewater are examples of alkalis. It is unusual for an element to react with both acids and alkalis. Such elements are said to be amphoteric. Aluminum also reacts quickly with hot water. In powdered form, it catches fire quickly when exposed to a flame.

Aluminum: Precious metal?

            Before chemists developed inexpensive ways to produce pure aluminum, it was considered a somewhat precious metal. In fact, in 1855, a bar of pure aluminum metal was displayed at the Paris Exposition. It was placed next to the French crown jewels!

Aluminum is an excellent conductor of electricity.

Occurrence in nature

            The abundance of aluminum in the Earth's crust is estimated to be about 8.8 percent. It occurs in many different minerals.

            Bauxite, a complicated mixture of compounds consisting of aluminum, oxygen, and other elements, is the primary commercial source for aluminum.

            Large reserves of bauxite are found in Australia, Brazil, Guinea, Jamaica, Russia, and the United States. The largest producer of aluminum metal is the United States; states that produce the most aluminum are Montana, Oregon, Washington, Kentucky, North Carolina, South Carolina, and Tennessee.

Isotopes

            Only one naturally occurring isotope of aluminum exists, aluminum-27. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

            Aluminum has six radioactive isotopes. A radioactive isotope gives off either energy or subatomic particles in order to reduce the atomic mass and become stable. When the emission produces a change in the number of protons, the atom is no longer the same element. The particles and energy emitted from the nucleus are called radiation. The process of decaying from one element into another is known as radioactive decay.

No radioactive isotope of aluminum has any commercial use.

Extraction

            Aluminum production is a two-step process. First, aluminum oxide is separated from bauxite by the Bayer process. In this process, bauxite is mixed with sodium hydroxide (NaOH), which dissolves the aluminum oxide. The other compounds in bauxite are left behind.

            The aluminum oxide is then treated with a process similar to the Hall method. There is not enough natural cryolite to make all the aluminum needed, so synthetic (artificial) cryolite is manufactured for this purpose. The chemical reaction is the same with synthetic cryolite as with natural cryolite. About 21

Aluminum alloys are used in the structural framing of buildings.

million metric tons of aluminum were produced in 1996 by this two-stage process.

Uses

            Aluminum is used as pure metal, in alloys, and in a variety of compounds. An alloy is made by melting and then mixing two or more metals. The mixture has properties different from those of the individual metals. Aluminum alloys are classified in numbered series according to the other elements they contain.

            The 1000 classification is reserved for alloys of nearly pure aluminum metal. They tend to be less strong than other alloys of aluminum, however. These metals are used in the structural parts of buildings, as decorative trim, in chemical equipment, and as heat reflectors.

            The 2000 series are alloys of copper and aluminum. They are very strong, are corrosion (rust) resistant, and can be

Aluminum alloys are commonly used in everyday kitchen utensils.

machined, or worked with, very easily. Some applications of 2000 series aluminum alloys are in truck paneling and structural parts of aircraft.

            The 3000 series is made up of alloys of aluminum and manganese. These alloys are not as strong as the 2000 series, but they also have good machinability. Alloys in this series are used for cooking utensils, storage tanks, aluminum furniture, highway signs, and roofing.

            Alloys in the 4000 series contain silicon. They have low melting points and are used to make solders and to add gray coloring to metal. Solders are low-melting alloys used to join two metals to each other. The 5000, 6000, and 7000 series include alloys consisting of magnesium, both magnesium and silicon, and zinc, respectively. These are used in ship and boat production, parts for cranes and gun mounts, bridges, structural parts in buildings, automobile parts, and aircraft components.

            The largest single use of aluminum is in the transportation industry (28 percent). Car and truck manufacturers like aluminum

Paint tubes are made from aluminum.

and aluminum alloys because they are very strong, yet lightweight. Companies are using more aluminum products in electric cars. These cars must be lightweight in order to conserve battery power. General Motors, Ford, and Chrysler have all announced advanced new car designs in which aluminum products will be used more extensively. Aluminum producers also plan to make a wider variety of wheels for both cars and trucks.

            Twenty-three percent of all aluminum produced finds its way into packaging. Aluminum foil, beer and soft drink cans, paint tubes, and containers for home products such as aerosol sprays are all made from aluminum.

            Fourteen percent of all aluminum goes into building and construction. Windows and door frames, screens, roofing, and siding, as well as the construction of mobile homes and structural parts of buildings rely on aluminum.

            The remaining 35 percent of aluminum goes into a staggering range of products, including electrical wires and appliances, automobile engines, heating and cooling systems, bridges, vacuum cleaners, kitchen utensils, garden furniture, heavy machinery, and specialized chemical equipment.

Compounds

            A relatively small amount of aluminum is used to make a large variety of aluminum compounds. These include:

            Aluminum ammonium sulfate (Al(NH ₄ )(SO ₄ ) ₂ ): mordant, water purification and sewage treatment, paper production, food additive, leather tanning

            Aluminum borate (Al ₂ O ₃ B ₂ O ₃ ): production of glass and ceramics

            Aluminum borohydride (Al(BH ₄ ) ₃ : additive in jet fuels

            Aluminum chloride (AlCl ₃ ): paint manufacture, antiperspirant, petroleum refining, production of synthetic rubber

            Aluminum fluorosilicate (Al ₂ (SiF ₆ ) ₃ ): production of synthetic gemstones, glass, and ceramics

            Aluminum hydroxide (Al(OH) ₃ ): antacid, mordant, water purification, manufacture of glass and ceramics, waterproofing of fabrics

            Aluminum phosphate (AlPO ₄ ): manufacture of glass, ceramics, pulp and paper products, cosmetics, paints and varnishes, and in making dental cement

            Aluminum sulfate, or alum (Al ₂ (SO ₄ ) ₃ ): manufacture of paper, mordant, fire extinguisher system, water purification and sewage treatment, food additive, fireproofing and fire retardant, and leather tanning

Health effects

            Aluminum has no known function in the human body. There is some debate, however, as to its possible health effects. In the 1980s, some health scientists became concerned that aluminum might be associated with Alzheimer's disease. This is a condition that most commonly affects older people, leading to forgetfulness and loss of mental skills. It is still not clear whether aluminum plays any part in Alzheimer's disease.

            Some authorities believe that breathing aluminum dust may also cause health problems. It may cause a pneumonia-like condition currently called aluminosis. Again, there is not enough evidence to support this view.

Ø    Tools And Materials

Number	Tools and materials	amount
1.	Tube reaction	5
2.	Spiritus lamp	1
3.	metal / aluminum tape	sufficient
4.	metal / magnesium ribbon	sufficient
5.	aluminum powder	sufficient
6.	universal indicator	sufficient
7.	anhydrous AlCl3	sufficient
8.	Al2O3	sufficient
9.	MgO	sufficient
10.	HCl liquid	sufficient
11.	HNO3 0,1 M and concentrated	sufficient
12.	amonium	sufficient
13.	Metal violet	sufficient
14.	MgCl2 0,1 M	sufficient

Ø    Procedure

a. Properties of Aluminum Hydroxide

1. In a test tube containing 2 ml solution of aluminum salt, add a few drops of ammonia. observe what is going forward to the addition of excess ammonia. observe whether there are changes.

2. in a tube containing 2 ml. aluminum salt solution, add a few drops of dilute NaOH. deposits that occur divided in two parts. the first part. forward the addition of NaOH to excess, while the other parts added with hydrochloric acid. observe what happens.

3. precipitated aluminum hydroxide is prepared by reacting an aluminum salt solution with a dilute NaOH solution. filtered precipitate is formed, then there is a paper filter sediment washed with cold water (pour cold water). to precipitate on the filter paper, pour the solution is colored, for example metilviolet. observe what happens.

b. compare aluminum chloride with magnesium chloride

1. heating anhydrous chloride, anhydrous aluminum chloride is heated in a test tube. observe what happens! repeat the experiment with the use of anhydrous magnesium chloride in place of anhydrous aluminum chloride. observe what happens.

2. input a scoop of anhydrous aluminum chloride into a test tube, then add water drop by drop. observe and measure its pH using universal indicator. repeat the experiment with anhydrous magnesium chloride in place of anhydrous aluminum chloride.

3. Insert the tube into a 0.1 gram ALO different reactions, each reaction tube was added with 3 ml of water observe what happens and check pH.

4. enter AlOH with 0.1 grams of magnesium oxide (MgO) in a test tube add HCl.

5. pour 3 grams of Al 0.1 M into a test tube and 3 ml of 0.1 M solution of Mg into another test tube. Check the pH of each solution with universal indicator.

6.added aqueous solution of sodium hydroxide to each tube.

Ø    Data

number	experiment	result
A. 1. 2. 3. B. 1. 2. C. 1. 2. 3. D. 1. 2.	properties of aluminum hydroxide 2 ml of saline solution is inserted into the aluminum tube is then added ammonia. 2 ml solution of aluminum incorporated into the test tube, then 14 drops of NaOH was added. then, the solution is divided into two: ·         The first drops of NaOH solution. ·         two drops of HCl solution solution of aluminum salts in a solution of NaOH reacted. then the solution was filtered. sediment was washed with ice water, then add 1 drop pp. anhydrous aluminum chloride is introduced into a test tube, then heated. anhindrat inserted into the aluminum tube, and then distilled water was added dropwise until the change. 0,1 grams of aluminum oxide is introduced into a test tube, then added 3 ml of water. 0,1 grams of aluminum oxide is introduced into a test tube, then added 0.5 N HCl for 3 ml 0.1 grams of aluminum oxide is introduced into a test tube, then added 3 ml NaOH. 3 ml of 0.1 M aluminum salt solution is inserted into a test tube, its pH was measured. then add 10 drops of NaOH. 3 ml of 0.1 M solution of magnesium introduced into the test tube, its pH was measured. then add 20 drops of NaOH.	·         precipitate formed and the first phase. ·         there are deposits. ·         14 drops ·         the sediment was lost. ·         3 drops ·         solution becomes more clear. ·         precipitate formed. ·         purple precipitate. ·         there is smoke. ·         vapor on the wall there. ·         the temperature became higher. ·         pH = 4 ·         clear solution. ·         there are deposits. ·         pH = 6. ·         clear solution. ·         there are deposits. ·         pH=1 ·         white turbid when shaken, when allowed to stand clear again ·         there are deposits. ·         pH=13 ·         there are deposits. ·         pH= 4 ·         there are deposits ·         pH=6

Ø  Discussion

a.       Properties of Aluminum Hydroxide

            In this experiment, the addition of a few drops of NH4OH to the solution will form a precipitate AlCl3 Al (OH) 3 a muddy color. When excess NH4OH was added, the precipitate formed becomes more turbid. This indicates that Al (OH) 3 was formed. This is in conformity with the theory that if the aluminum salt is reacted with ammonia it will form a precipitate Al (OH) 3 which, when added slightly excess precipitation will be complete by the equation:
                                    AlCl3 + 3 NH4OH → Al (OH) 3 + 3NH4

            In the next experiment, the addition of several drops of NaOH to the solution will produce a precipitate AlCl3 Al (OH) 3 a muddy color. Then the precipitate formed is divided into two parts where the first part is added to aqueous HCl led to the solution became clear (late again) and the second part was added with excess NaOH that also led to the solution became clear (late again). This is in conformity with the theory that if added  aluminum salt with a base (alkali hydroxide) will form a precipitate Al (OH) 3 which, when added to an excess of acid or alkali hydroxides formed dissolved lead back to the equation:

                                    3NaOH + AlCl3 → Al (OH) 3 + 3NaCl

                                    Al (OH) 3 + AlCl3 + 3H3O → 3HCl

                                    Al(OH)3 + NaOH → Na [Al (OH) 4](Sodium tetraaminhidroksoaluminat)
            In the next experiment, the addition of NaOH to AlCl3 solution will produce a precipitate of Al (OH) 3 which is then filtered and washed with distilled water after it was added with methyl violet (purple) produces a purple powder. Methyl violet has a stretch of about 0.5 to 1.5 pH. If pH <0.5, would indicate a change to yellow if the pH is> 1.5 then it would indicate a change to purple.It can be concluded that the deposition of Al (OH) 3 is acidic with a pH> 1.5
           

            b. Comparing Aluminum Chloride and Magnesium Chloride

            In this experiment, powdered aluminum chloride, anhydrous AlCl3 is heated to form a white powder and a little yellow powder. While magnesium chloride MgCl2 powder when heated to form a silver-colored powder. In theory, both the powder will melt and it was different.         MgCl2 powder melts faster than MgCl2 AlCl3 as having a smaller density compared with AlCl3.

            In this experiment, anhydrous AlCl3 drops with water to produce a mixture which does not dissolve when the pH was measured, showed pH = 1 (acid) which when added to excess water to dissolve. This is in conformity with the theory that if the solid AlCl3 dropwise with an excess of water will produce an acidic solution with pH 2-3 or lower if the more concentrated solution is obtained. Reaction occurs:

                                    AlCl3 (s) + 6H2O (l) → [Al (H2O) 6] 3 + (aq) + 3Cl-(aq)

            At the time of the water drops of anhydrous MgCl2, MgCl2 insoluble and pH were measured at the time showed pH = 8 (base) which when added to excess water remains insoluble. It is not in accordance with the theory that water-soluble MgCl2 produces a weak acid (pH = approximately 6) by the equation:

                                    MgCl2 (s) + 6H2O → [Mg (H2O) 6] 2 + (aq) + 2Cl-(aq)

Acid-Base Properties compare Al2O3 and MgO

            In this experiment, MgO was added to a solution of white water, slightly soluble, with pH = 9 (base), while Al2O3 was added to IAR, is not soluble with pH = 7 (neutral). This is in conformity with the theory that if the MgO powder is reacted with water to form Mg (OH) 2 is only slightly soluble. However, if testing the pH of the solution will be found pH = 9 (alkaline). Reaction occurs:

                                    MgO + H2O → Mg (OH) 2

            After the theory, Al2O3 can not react with water and insoluble in water. Although it still contains oxide ion, but too strong in the lattice solids to react with water.

            In the next experiment, Al2O3 reacted with HCl, is not soluble in pH = 1 is currently treated with NaOH, insoluble in pH = 9. It is not in accordance with the theory that Al2O3 can react with dilute hydrochloric acid produces AlCl3 which shows the basic side of its amphoteric nature, while if it reacts with a base will produce sodium tertahidroksoaluminat showing the acid side of its amphoteric nature. Premises of the equation:

 Al2O3 + 3H2O 2AlCl3 + 6HCl → Al2O3 + NaOH → 2Na [Al (OH) 4]

            However, it is (not the reaction of Al2O3 with NaOH and HCl) may occur if used Al2O3 derived from heating Al (OH) 3 at temperatures above 850 oC. in theory, if the temperature is above 850 oC making, the oxide formed is not soluble in acid or base so that when the pH was measured, instead of Al2O3 is legible but the pH of HCl and NaOH pH itself.
When MgO is reacted with HCl, insoluble and pH = 1 was with NaOH, slightly soluble in pH = 13. It is not in accordance with the theory that MgO will react with HCl to give a solution MgCl2 indicating the base of the oxide with the reaction equation:

                                                MgO + 2HCl → MgCl2 + H2O

Whereas MgO will not react with NaOH.

d. Compare the properties of aluminum and magnesium ions base

            In this experiment, the initial pH of AlCl3 is 3 MgCl2 While the pH level of 5. From these results it can be seen that AlCl3 is more acidic than MgCl2. This is because AlCl3 derived from strong acids and weak bases, while MgCl2 derived from strong acids and strong bases.
After that, NaOH was added to each solution to form a solution of AlCl3 turbid (diluted), which is precipitated Al (OH) 3, while MgCl2 to form turbid solution (thick) with the equation:

                                                3NaOH + AlCl3 → Al (OH) 3 + 3NaCl

                                                2NaOH + MgCl2 → Mg (OH) 2 + 2NaCl

            This is in conformity with the theory that if a solution of aluminum and magnesium salts (AlCl3 and MgCl2) is reacted with a base (NaOH) will form a precipitate Al (OH) 3.

Ø  Conclusion

1). Aluminum hydroxide, Al (OH) 3 is soluble in acid or alkaline pH is ammonia to form Al

(OH) 3 (complete deposition)

2). Al (OH) 3 is acidic

3). Al2O3 is not soluble in water and are amphoteric

4). AlCl3 acidic than MgCl2

b. Suggestion

           It is expected that the next praktikan more carefully and thoroughly as practical in order to obtain the expected results

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