A. TITLE : Aluminum
B. DATE OF EXPERIMENT :
Start : Tuesday, 6st November 2012, at 8.00 a.m
Finish : Tuesday, 6th November 2012, at 10.00 a.m
C. OBJECTIVES :
Knowing properties of aluminium and their compound
D. BASIC THEORY
Aluminum is a silvery white member of the boron group of chemical elements. It has the
symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances.
Aluminum is the third most abundant element (after oxygen and silicon), and the most abundant
metal, in the Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminum
metal is too reactive chemically to occur natively. Instead, it is found combined in over
270 different minerals. The chief ore of aluminum is bauxite. Aluminum is remarkable for the
metal's low density and for its ability to resist corrosion due to the phenomenon of passivation.
Structural components made from aluminum and its alloys are vital to the aerospace industry and
are important in other areas of transportation and structural materials. The most useful compounds of
aluminum, at least on a weight basis, are the oxides and sulfates.
Physical characteristic
Pure aluminum is silvery white metal having the desired characteristics of the metal. It is
mild, not magnetic and not easily splashed, is the second easiest in terms of metal forming, and
sixth in terms of ductility. Aluminum is a soft, durable, lightweight, ductile and malleable metal
with appearance ranging from silvery to dull gray, depending on the surface roughness.
Aluminum is nonmagnetic and does not easily ignite. A fresh film of aluminum film serves as a
good reflector (approximately 92%) of visible light and an excellent reflector (as much as 98%) of
medium and far infrared radiation. The yield strength of pure aluminum is 7–11 MPa, while
aluminum alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminum has about
one-third the density and stiffness of steel. It is easily machined, cast, drawn and extruded. Corrosion
resistance can be excellent due to a thin surface layer of aluminum oxide that forms when the
metal is exposed to air, effectively preventing further oxidation. Aluminum is a good thermal and
electrical conductor, having 59% the conductivity of copper, both thermal and electrical.
Amphoteric
In chemistry, an amphoteric species is a molecule or ion that can react as an acid as well
as a base. The word is derived from the Greek word amphoteroi meaning "both". Many metals
(such as zinc, tin, lead, aluminum, and beryllium) and most metalloids have amphoteric oxides or
hydroxides. One type of amphoteric species are amphiprotic molecules, which can either donate
or accept a proton (H+). Examples include amino acids and proteins, which have amine and
carboxylic acid groups, and self-ionizable compounds such as water and ammonia. Ampholytes
are amphoteric molecules that contain both acidic and basic groups and will exist mostly as
zwitterions in a certain range of pH. The pH at which the average charge is zero is known as the
molecule's isoelectric point. Ampholytes are used to establish a stable pH gradient for use in
isoelectric focusing.
Aluminum hydroxide:
Base (neutralizing an acid): Al(OH)3 + 3HCl → AlCl3 + 3H2O
Acid (neutralizing a base): Al(OH)3 + NaOH → Na[Al(OH)4]
Aluminum oxide
With acid: Al2O3 + 3 H2O + 6 H3O+(aq) → 2 [Al(H2O)6]3+(aq)
With base: Al2O3 + 3 H2O + 2 OH-(aq) → 2 [Al(OH)4]-(aq)
Al(OH)3 is amphoteric. It reacts principally as abase, i. e. it reacts with acid to form salts
that contain the [Al(H2O)6]3+ ion. However, Al(OH)3 show some acid properties when dissolves
in NaOH, forming sodium aluminate. (Howeve, Al(OH)3 is precipitated by the addition of carbon
dioxide, showing that the acidic properties are very weak).
Explaining the properties of aluminum oxide can cause confusion because it can be in
several different forms. One form is not very reactive. It is known chemically as alpha-Al2O3 and
produced at high temperatures. In this discussion we use one of the reactive forms. Aluminum
oxide is an amphoteric compound. Meaning can react either as bases or acids.
Reaction of aluminum
Aluminum dissolve in dillute mineral acids libereting hydrogen.
2 Al (s)+ 6HCl (aq) 2AlCl3 (aq)+ 3H2 (g)
However, concentrated HNO3 renders the metal passive because itis an oxidizing agent and
produces a protective layer of oxide on the surface. Aluminum also dissolve in aqueous
NaOH(and therefor amphoteric), liberating hydrogen and forming aluminates.
2Al (s) + 2 NaOH (aq) + 6 H2O (l) 2 NaAl(OH)4 (aq) or 2 NaAlO2.2H2O (aq) + 3 H2 (g)
Reaction with water
Aluminum oxide cannot simply react with water such as sodium oxide and magnesium oxide,
and insoluble in water. Although it still contains oxide ions, but it too strong to be in a solid
lattice to react with water.
Reaction with acid
Aluminum oxide-containing oxide ions, so that it can react with acids such as sodium or
magnesium oxide. That is, for example, aluminum oxide will react with dilute hydrochloric
acid solution of aluminum chloride produces heat. In this case (and similarly in the reaction
with another acid), aluminum oxide shows the base of the nature it’s amphoteric
Reaction with bases
Aluminum oxide can also show acidic properties, can be seen in the reaction with a base such
as sodium hydroxide. Various aluminates can be formed - a compound in which aluminum is
found in the negative ion. This is possible because aluminum has the ability to form covalent
bonds with oxygen. In the example of sodium, electronegativity difference between
sodium and oxygenate too big to form ionic bonds other than bonds. But he electronegativity
increases in one period - so the difference in electronegativity between aluminum and oxygen
is smaller. This leads to the formation of covalent bonds between them. With concentrated
sodium hydroxide solution a hot solution of aluminum oxide reacts to produce sodium
tetrahydroxoaluminate colorless.
Usefulness
Aluminum is almost always alloyed, which markedly improves its mechanical
properties, especially when tempered. For example, the common aluminum foils and beverage cans
are alloys of 92% to 99% aluminum.
Some of the many uses for aluminum metal are in:
Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles,
etc.) as sheet, tube, castings, etc.
Packaging (cans, foil, etc.)
Construction (windows, doors, siding, building wire, etc.)
A wide range of household items, from cooking utensils to baseball bats, watches.
Street lighting poles, sailing ship masts, walking poles, etc.
Washed Rubbed with HgCl2
Entered into reaction tube + NaOH 2 M
H2 gas
Aluminum plat
Result
Outer shells of consumer electronics, also cases for equipment e.g. photographic
equipment.
aluminum can be reacted with hydrochloric acid or with sodium hydroxide to
produce hydrogen gas.
E. TOOLS AND MATERIALS
Tools
No.
Materials Amount
1 Porcelain bowl 12 Pipettes 23 Test tube 5,24 Funnel 15 Rack 1
Materials
No Materials1 NaOH solution 0,1M 2 NaOH solution 1 M 3 HgCl2 solution 4 HCl solution 0,1 M 5 Na2CO3 solution 6 Al solid 7 Litmus paper 8 Cotton 9 Filter paper
F. PROCEDURE
1.
Aluminum plate
Entered into test tube 2 Added of HCl
CO2 gas H2 gas H2 gas
Entered into test tube 3 Added of NaOH
Entered into test tube 1 Added of Na2CO3 hot
Al2(SO4)3 soution
Tested with litmus paper
Result
1 mL of Al2(SO4)3 solutionor tawas solution
Poured into test tubeAdd NaOH solution 2 M drop by drop
Precipitation
Precipitationdissolved
Add NaOH solution 2 M drop by drop again until
Precipitation
Precipitationdissolved
Add HCl solution 0,1 M drop by drop again
Add HCl solution 0,1 M drop by drop again until
2.
3.
4.
Al2(SO4)3 solution
Result
Filtrate Residue (precipitate)
Add little bit (NH4)2SFilter the precipitate
Wash with a hot water so manyMove into a test tube with a little bit waterAdd with NaOH solution drop by drop until residue dissolve
5.
G. DATA EXPERIMENT
No Procedure Result Reaction Conclusion
Washed Rubbed with HgCl2
Entered into reaction tube + NaOH 2 M
H2 gas
Aluminum plat
Result
1. Al plate: silver-shiny
NaOH: colorless
HgCl2: colorless
Al + NaOH: there is
H2 gas
After washed by
water and rubbed by
HgCl2, Al plate
become shiny (+++)
2Al(s) + 2NaOH(aq) +
6H2O(e)
2NaAl(OH)4(aq) +
3H2(g)
3HgCl2(aq) + 2Al(s)
2AlCl3(aq) + 3Hg(s)
When aluminium is
reacted by NaOH, it
will produce hydrogen
gas
When added by HgCl2,
it will make
aluminium shiny
Aluminum plate
Entered into test tube 2 Added of HCl
CO2 gas H2 gas H2 gas
Entered into test tube 3 Added of NaOH
Entered into test tube 1 Added of Na2CO3 hot
Al2(SO4)3 soution
Tested with litmus paper
Result
2. Al plate: silver-shiny
Na2CO3: colorless
HCl: colorless
NaOH: colorless
Al + NaCO3: there is
CO2 gas (++++)
Al + HCl: there is H2
gas (+)
Al + NaOH: there is
H2 gas (++)
2Al(s) + 2NaOH(aq) +
6H2O(l)
2NaAl(OH)4(aq) +
3H2(g)
6HCl(aq) + 2Al(aq)
2AlCl3(aq) + 3H2(g)
2Al(s) + Na2CO3(aq)
2NaAlO2(aq) + 2CO2
Aluminium react with
Na2CO3 and produce
CO2 gas
Aluminium react with
NaOH and HCl
produce H2 gas
3. Al2(SO4)3: colorless
Litmus paper: blue
red and red red
Al2(SO4)3(aq) 2Al3+
(aq) + 3SO22-
(g)
It is indicate acid
solution
1 mL of Al2(SO4)3 solution
or tawas solution
Poured into test tubeAdd NaOH solution 2 M drop by drop
Precipitation
Precipitationdissolved
Add NaOH solution 2 M drop by drop again until
Precipitation
Precipitationdissolved
Add HCl solution 0,1 M drop by drop again
Add HCl solution 0,1 M drop by drop again until
4. Al2(SO4)3: colorless
NaOH: colorless
HCl: colorless
Al2(SO4)3 + NaOH: 4
drops to form white
precipitate (+), 10
drops to dissolve, the
solution is colorless.
Al2(SO4)3 + NaOH +
HCl: 8 drops to form
white precipitate (++
+), 40 drops to
dissolve, the solution
is colorless
Al2(SO4)3(aq) +
6NaOH(aq)
2Al(OH)3(s) +
3Na2SO4(aq)
Al(OH)3(s) +
NaOH(aq)
NaAl(OH)4(aq)
NaAl(OH)4(aq) +
HCl(aq) Al(OH)3(s) +
H2O +NaCl(aq)
NaAl(OH4)(aq) +
HCl(aq) Al(OH)3(s)
+H2O(l) +NaCl(aq)
Aluminium has an
amphoter
characteristic.
It can react with base
(NaOH) to form
precipitate and
dissolve excess NaOH
Then it become
precipitate again when
added by acid (HCl)
5. Al2(SO4)3: colorless
(NH4)2S: colorless
NaOH: colorless
Al2(SO4)3 +
(NH4)2S: white
precipitate of
Al(OH)3
Residue: white
After dropped by
NaOH: residue is
dissolve
Al2(SO4)3(aq) +
(NH4)2S
2Al(OH)3(s) + H2S(g)
+ (NH4)2SO4(aq)
Al(OH)3(s) +
NaOH(aq)
NaAl(OH)4(aq)
The reaction between
Al2(SO4)3 and
(NH4)2S produce H2S
gas that has unwell
odder
The precipitate of
Al(OH)3 when reacted
by HaOH produce
aluminates
Result
Al2(SO4)3 solution
Filtrate Residue (precipitate)
Add little bit (NH4)2S Filter the precipitate
Wash with a hot water so many
Move into a test tube with a little bit water
Add with NaOH solution drop by drop until residue dissolve
H. ANALYSIS
The first experiment
The objective of the first experiment is to identify chemical characteristic of
aluminum. The silver aluminum piece is added with NaOH. There is much bubbles on it.
This bubbles is H2 gas that is shown by reaction below ,
2Al(s) + 2NaOH(aq) +6H2O (l) 3 H2(g) + 2NaAl(OH)4(aq)
Then, it is washed in order to remove the dirty things that stick on the aluminum. When it is
rubbed with colorless solution of HgCl2, the surface of aluminum is become bright and shiny
that can be seen in the reaction below
3HgCl2(aq) + 2Al(s) 2AlCl3(aq) + 3Hg(s)
The reduction reaction happen, where Al become Al3+and Hg2+ become Hg. It indicates that
the reaction is spontaneous. It can be proved as follow
Hg2+ + 2e Hg Eo = 0,92 V
Al3+ + 3e Al Eo = -1,66V
Eocell= 0,92+1,66 = 2,58V
The positive sign indicates that it runs spontaneously
The second experiment
The objective of the second experiment is to identify the characteristic of
aluminum when react with acid, base and salt. There are three test tubes.
a. In the first test tube , a piece of aluminum is added by colorless and hot solution of
Na2CO3. The bubbles appear, it means that CO2 gas is formed based on reaction
below
Al(s) + Na2CO3(aq) NaAlO2(aq) + CO2(g)
The Na2CO3 must be heated before because it can’t react in cold condition.
b. In the second test tube, a piece of aluminum is added by colorless solution of HCl.
Same with the previous tube, the bubbles appear but different gas formed. Gas
formed in this experiment is H2 gas based on reaction below,
6HCl(aq) + 2Al(s) 2AlCl3(g) + 3H2(g)
c. In the third test tube, a piece of aluminum is added by colorless solution of NaOH.
Basicly it is same with the second experiment that H2 gas is formed, and the reaction
is
6NaOH(aq) + 2Al(s) 3 H2(g) + 2Na3AlO3(aq)
The third experiment
The aim of third experiment is to know the characteristic of Aluminum Sulfate. In this
experiment there was Aluminum Sulfate (Al2(SO4)3) that be tested with red and blue litmus
paper. The changing of litmus paper was occurs in blue litmus paper. This litmus paper
change from blue becomes red, while the red litmus paper wasn’t changing. It indicate the
acidic of Aluminum Sulfate (Al2(SO4)3). The reaction is:
Al2(SO4)3 (aq) 2Al3+ (aq) + 3SO4 2- (aq)
The fourth experiment
The aim is to identify the amphoteric characteristics of aluminium Al2(SO4)3 is can as an
acid in strong base condition and as base in strong acid condition, by added NaOH 2M
firstly 4 drops is shown turbid solution and there are white precipitation (+) its indicate that
formed Al(OH)3. By using acid-base theory Brownsted-Lowry, this test shows the Al (OH)3
have acid properties reaction. The reaction that is occur as below:
Al2(SO4)3(aq) + 6NaOH(aq) 2Al(OH)3(s)+3Na2SO4(aq)
After that, we added till 10 drops of NaOH, The compound of Al (OH)3 donates its
protons to hydroxide ion forms a complex [Al(OH)4]- while the hydroxide ion acts as a
proton acceptor that is base. it show the color of solution become colorless. The reaction that
support is as bellow :
Al(OH)3(s) + NaOH(aq) NaAl(OH)4(aq)
In that reaction, can be known that Aluminum hydroxide that have characteristic is
amphoteric so, it can dissolve with NaOH and formed complex compound Na[Al(OH)4] is
attempt as sodium tetrahidroksoaluminat that colorless. Complex compound is usually
formed from cations of transition element, but in that reaction sodium which is IA group can
formed complex compound. That is because alkali metal have first ionization potential lower
enough so it is easier to formed ion with charge +1. In alkali metals compound, generally
have oxidation number is +1. Alkali metal ions is difficult to formed complex ion with
simple anions or monodentate neutral ligand. But, with salt from polidentate ligand, alkali
metals can formed more stable complex compound.
Then, after the solution become colorless, we add 8 drops of HCL 1M, there is white
precipitate (+++), the kind of precipitation is Al(OH)3 :
NaAl(OH)4(aq)+ HCl(aq) Al(OH)3(s) +H2O(l)+NaCl(aq)
After, that we still add HCl 1 M till 40 drops, the solution become colorless again, the
reaction that support is as bellow:
NaAl(OH4)(aq) + HCl(aq) Al(OH)3(s) +H2O(l) +NaCl(aq)
This is possible because aluminum has ability to form covalent bonds with oxygen. The
reaction above is a reversible reaction, which would reduce the reagents and every hydroxyl
ions that enough will caused reaction goes from right to left, forming Al(OH)3.
The fifth experiment
The fifth experiment was done to prove the aluminum compounds can form
complexes. To that end, the steps it works is adding a solution of (NH4)2S to a solution of
Al2(SO4)3. Of the reaction, the resulting solution was initially clear colorless to white turbid
form white precipitates of Al(OH)3 and also there is odor that not good. The not good odor is
caused by the H2S gas. Furthermore precipitate formed is filtered and the residue washed
using hot water to remove the ammonium sulfate that still remains in it. So the equation
would be:
2Al2(SO4)3 (aq)+(NH4)2S (aq)2Al(OH)3 (s)+H2S↑ (g)+(NH4)2SO4 (aq)
After washing, the precipitate was treated with a solution of NaOH which ultimately
makes the precipitate soluble compound and allegedly formed. . It can be shown as reaction
below:
Al(OH)3(s) NaAlO2.2 H2O(aq)
or
Al(OH)3(s) + NaOH(aq) → Na[Al(OH)4](aq)
Aluminum compounds are able to form complexes Na[Al(OH)4] as three positive
aluminum ions have a very high hydration enthalpy is -4665 kJ/mole which contains not
only Al3+ ions but in form [Al(H2O)6]3+. Al3+ ion is relatively small in size, but because it has
a high ion charge (+3) as well as its charge density, cation in aqueous solution is able to
accommodate six neutral H2O molecules (which are polar with the negative pole of the O
atoms lead to metal ion) produces complex ion [Al(H2O)6]3+ octahedron shaped. Aluminate
ion is AlO2- or Al[(H2O)2(OH4)]- where Al3+ cation is surrounded by four negative ions OH-
and two polar molecule H2O. around the metal ion that is considered too high negative
charge. This resulted in unstable complexes that two molecules of H2O is removed and a
complex compound of formula [Al(OH4)]- which means adopting tetrahedron shape. The
explanation is to explain why Al which is the main group elements is capable of forming
complex compounds
I. REFERENCE:
Amaria, M.Si, dkk. 2012. Penentuan Praktikum Kimia Organik II Unsur-unsur Golongan
Utama. Surabaya: Unipress.
Lee, J.D. Concise Inorganic Chemistry Fourth Edition.New York:Chapman & Hall
Vogel. (1985). Buku Teks Analisis Anorganik Kualitatif Makro dan Semimakro. Jakarta : PT.
Kalman Media Pusaka
Muchlis,dkk. 2012. Handouts Kimia Anorganik II. Surabaya : jurusan Kimia FMIPA
UNESA
Sugiyarto,Kristian H. 2003. Common Textbook Kimia Anorganik II.Yogyakarta :Jica.
Anonymous. 2012. Aluminum (Online). http://en.wikipedia.org/wiki/Aluminium. Accessed on
09 November 2012.
Anonymous. 2012. Amphoteric (Online). http://en.wikipedia.org/wiki/Amphoterism. Accessed
on 09 November 2012.
J. ANSWER QUESTION
1. Explain the amphoteric characteristic of alumunium based on your experiment !
Answer :
a. Reaction with base (NaOH)
Al(OH)3(s) + NaOH(aq) NaAl(OH)4(aq)
From the reaction above, we know Al(OH)3 donor its proton to hydroxide ion of
NaOH to form complex compound NaAl(OH)4
b. Reaction with acid (HCl)
Al(OH)3(s) + 3HCl(aq) AlCl3(aq)+3H2O(l)
From the turbid solution change to colorless solution . Al(OH)3 act as base because it
accept proton.
Based on reaction above, the Al(OH)3 can react well with acid and base, so its have
ampotheric characteristic, it accept and donor proton.
2. Write the reaction equation that is happen n your experiment!
First experiment
1. 2Al(s) + 2NaOH(aq) + 6H2O(l) 2NaAl(OH)4(aq) + 3 H2(g)
2. 3HgCl2(aq) + 2Al(s) 2AlCl3(aq) + 3Hg(s)
Second experiment
1. 2Al(s) + 2NaOH(aq) + 6H2O(l) 2NaAl(OH)4(aq) + 3H2(g)
2. 6HCl(aq) + 2Al(aq) 2AlCl3(aq) + 3H2(g)
3. 2Al(s) + Na2CO3(aq) 2NaAlO2(aq) + 2CO2
Third experiment
Al2(SO4)3 (aq) 2Al3+ (aq) + 3SO2 2- (g)
Fourth experiment
1. Al2(SO4)3(aq) + 6NaOH(aq) 2Al(OH)3(s)+3Na2SO4(aq)
2. Al(OH)3(s) + NaOH(aq) NaAl(OH)4(aq)
3. NaAl(OH)4(aq)+ HCl(aq) Al(OH)3(s) +H2O(l) +NaCl(aq)
4. NaAl(OH4)(aq) + HCl(aq) Al(OH)3(s) +H2O(l) +NaCl(aq)
Fifth experiment
1. 2Al(SO4)3(aq) +(NH4)2S 2Al(OH)3(s)+H2S(g) +(NH4)2SO4(aq)
2. Al(OH)3(s) + NaOH(aq) NaAl(OH)4(aq)
3. Explain the used of aluminum!
Aluminum metal is moderately soft and weak when pure, but is much stronger when
alloyed with other meals. Its main advantage is its lightness (low density 2.73 gcm -1).
Some alloys are used for special purpose: duralumins which contain about 4% Cu, and
several aluminum bronze (alloys of Cu and Al with other metals such as Ni, Sn, and
Zn). The metal produced in the largest quantity is iron/steel but the production of
aluminum is second largest. There are any uses for aluminum and its alloys:
1. As structural metals in aircraft, ships, cars, and heat exchanges.
2. In building (doors, windows, cladding panels and mobile homes).
3. Container such as cans for drinks, tube for toothpaste and metal foil.
4. For cooking utensils.
5. To make electric power cables (on a weight basis used in preparing aluminum paint.
6. Conduct twice as well as copper).
7. Finely divided aluminum powder is called “aluminum bronze’, and is used in
preparing aluminum paint.