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.