May, 5th 2015

EXPERIMENT VIIIALUMINIUM AND ITS COMPOUNDS

A. ObjectivesStudy the properties of aluminium metal and its compounds.

B. Theoritical BasicPure aluminum is a silvery-white metal with many desirable characteristics. Aluminium

lightweight, nontoxic (as the metal), nonmagnetic and not splashed. Aluminium is very malleable and less harsh. Aluminum is an active metal as shown on the price of its reduction potential and is not found in its elemental form in nature. Aluminum is the third most elements in the earth's crust, but is not found in the form of free elements. Although most aluminum compounds found in nature, for many years was not found an economical way to obtain aluminum metal from its compounds (Ahmad, 2001).

Aluminium is metal white clay and can be forged, gray powder. He fused at 659˚C. When exposed to air, oxidized aluminum obejk objects on the surface, but this oxide layer protects the object of further oxide. Dilute hydrochloric acid easily dissolves these metals, slower dissolution in dilute sulfuric acid or dilute nitric acid (Keenan, 1984).

Aluminum properties : Aluminum is a silvery white metal and is very light, has a thermal conductivity and high electrical conductivity. Some chemical reaction of aluminum.1. Easy to burn in the flame and high heat generating reaction.2. Reacts with acids to produce hydrogen gas.3. Reacts with strong bases, especially bases alkali produces H2 gas.4. With this metal air to form a strong oxide layer on the surface which can protect the metal from further oxide. Hence it is said to be resistant metal rust (corrosion) and is used to coat other metals to resist rust (Svehla, 1985).

The properties of aluminium metal is heavily influenced by density of Al3+ ion charge. Density of ion charge is a charge ratio of the ion radius. Compared with alkali metals and alkaline earth metals, Al has the largest density density of ion charges. Aluminium is somewhat less reactive than expected with a very negative electrode potential (E0 = - 1.66 volt). Al does not react with water or moisture, as is normally protected by an Al oxide layer that is very thin but very stable. If the oxide layer is chemically removed, ie scrubbing with a solution of HgCl 2, Al metal reacts rapidly with atmospheric moisture and exothermic produce aluminium oxide.(Inorganic Chemistry Lecturer Team, 2015)

Density of ion charge

Cation Charge Ion radius (nm) Density of ion charge

Na +1 0.098 10

Mg +2 0.065 31

Al +3 0.048 63

Zn +2 0.074 27

Cu +2 0.069 29

C. Equipment and MaterialEquipment :

1. Test tube2. Beakerglass3. Bunsen burner

Materials :1. Diluted HCl2. Some pieces of metal Al3. HgCl2 solution of 0.1 M (in ethanol solvent)4. 0.1 M NaOH solution

D. Work InstructionExperiment 1(Reaction with HCl)

Experiment 2 (Reaction with NaOH)

Experiment 3 (Reaction with Oxygen)

2 ml of dilute HCl put in a test tube

some pieces (3-4) metal Al put into

that

If Al has not dissolved after 5

minutes, the mixture heated

observe and record changes

that occur

2 ml of aqueous NaOH solution in

a test tube

some pieces metal Al put into that

If Al has not dissolved after 5

minutes, the mixture heated

observe and record changes

that occur

E. Result of observation1. Changes in experiment 1 :

Al metal in HCl 2 ml : not any occurs, Al disappear.Al in HCl heated : there are bubbles.Reactions : 2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g)

2. Changes in the experiment 2 :Al metal in NaOH 2 ml : there are bubbles, Al disappear.Al in HCl heated : there are bubbles.

Reactions :2Al(s) + 5OH-

(aq) + 3H2O (l) → 2[Al(OH)4]-(aq) + 3H2 (g)

3. Changes in the experiment 3 :Aluminium foil in HgCl : not any occurs can looked, but aluminium foil more shiny.Then washing in water, and leaf in open air : the color become gray like as dust, there are fiber cover the pieces.Reactions :

Al2O3(s) + 3HgCl2(aq) → 2AlCl3(aq) + 3HgO(s)

4Al(s) + 3O2(g) → 2Al2O3(s)

Al2O3(s)   +  2OH-(aq)   +   7H2O(l) → 2[Al(OH)4(H2O)2]-

(aq)

2[Al(OH)4(H2O)2]-(aq)  +  H2O(l) + CO2(g) → 2[Al(OH)3(H2O)3](s)   +  CO3

2-(aq)

F. Questions1. Experiment 1

a. Why is Al a bit slow to react, whereas a negative value reduction potential?b. Without the use of indicators, explain how the nature of the solution occurs. Explain

why this is so?Answer :

a. Al less reactive metal that needs heating, it because Al in basically.b. Al in HCl not react (not produce bubbles) before heated, and after it’s heated can react

with the show of bubbles.2. Experiment 2

a. What gas is formed? Compared with the results of an experiment, which resulted more?

a piece of aluminium foil

put in a glass and dropped with

HgCl2 solution

allow a few minutes, then

wash aluminium foil

aluminium foil leaf in the open air

observe and record changes the

changes

b. Why the pan made of Al may not be washed with soda (Na2CO3)Explain by shhowing this reaction!Answer :

a. The gas formed is H2 gas. Gas produced in the experiment number two more than the experimental one because according to the nature of the metals Al is able to react with a strong base, especially bases alkali produces H2 gas.

b. Al pans should not be washed with washing soda (Na2CO3) because when aluminum pans are washed with Na2CO3 will be damaged and reacts with Na2CO3 so that a layer of aluminum would be eroded.

3. Experiment 3a. Why HgCl2 solution is able to clean the surface of the aluminium foil effectively?b. The process of Al → Al3+ and O2 is endothermic. Why it formed Al2O3 and explain why

these substances are very stable.c. Give some examples of the use of metallic Al. Explain and state the nature of Al which

determined its use for various appliances.Answer :

a. HgCl2 can clean aluminum foil layer effectively as HgCl2 tersbebut can release sesuia aluminum oxide layer of the reaction:

HgCl2( aq)+Al2O3( s )→ AlCl3+3 HgO

b. It formed Al2 O3 becauce when Al react with airformed thick layers of oxides Al2 O3

yang which protect oxides.Al2 O3 stable cause difficult to react with air in a round, also difficult react with acid an base nonconcentrated and acid concentrated.

c. Some examples of the use of metallic Al: for coating cookware, food packaging, electrical wiring, basic construction materials in order, good buildings, cars, and airplanes. Al trait among others, non-toxic, light weight, large electrical conductivity, as the reductant, reflective, corrosion resistant air.

G. DiscussionThis experiment to understand about characteristics of aluminium and it’s compound.

Practicant do 3 test to know that. They are reaction with HCl, reaction with NaOH, and reaction

with oxygen.

1. Reaction with HCl

To know about reactivity of Al in strong acid solution, we use HCl. Dilute HCl prepared

in test tube, then Al metal put into HCl. After 5 minutes, not any changes. So we need heated it.

After that, on side of aluminium pieces there are bubbles. The metal is float in solution, it is

different before heated the metal is disappear in solution.

The result of observation has means that Al metal react with strong acid by heated. So it

need high temperature to react. If Al can react with acid, so Al have base characteristics. Look

at this reaction :

2Al(s) + 6HCl(aq)∆→

2AlCl3(aq) + 3H2(g)

We can know that bubbles are H2 gasses, the solution become AlCl3 solution. So the solution

still colorless.

2. Reaction with NaOH

To know about reactivity of Al in strong base solution, we use NaOH solution. Dilute

HCl prepared in test tube, then Al metal put into HCl. After 5 minutes, there any changes. The

metal are covered by bubbles. It means Al metal can react with strong base (without heating). If

Al can react with base, so Al have acid characteristics. Look at this reaction :

2Al(s) + 5OH-(aq) + 3H2O (l) → 2[Al(OH)4]-

(aq) + 3H2 (g)

The bubbles produced in reaction is same with experiment-1, that is H2 gasses. Produce of this

reaction is complex solution.

Then we also test it by heating. The bubbles are increase, and it still colorless. Before

heating the metal are disappear, but when heated it is floating.

After that we can know, Al metal can react with acid and base. So it is amfoter, but Al

more reacted with base than acid. That means Al has more acid characteristics, than base

characteristics.

3. Reaction with oxygen

This experiment is to know characteristics of Al metal if react with oxygen in free

atmosphere. At reaction with HCl and NaOH, practicant use Al metal. But in this experiment

practicant use aluminium foil paper. So the aluminium in this experiment already in their

oxidant.

Aluminium foil paper dropped with HgCl2 solution. HgCl2 solution is toxic and bad for

healthy people. Practicant must save them self, so reaction with HgCl2 do in close room. Look

at this reaction :

Al2O3(s) + 3 HgCl2(aq) → 2 AlCl3(aq) + 3 HgO(s)

From that reaction, we can know that aluminium can react with HgCl2. The product HgO

cover the metal, so it more shiny. So HgO used for cleaning aluminium surface.

After that the aluminium foil washed in water. based on theory HgO very easy disolve in

water, so cover HgO is lost. Because of losting HgO, aluminium not any cover. So aluminium

direct contact with oxygen in atmosphere. If Al contact with oxygen, it can formed Al2O3. Look

at this reaction :

2Al(s) + 3/2O2(g) Al2O3(s)

From that reaction, we can know that aluminium forming oxide of Al, it has powder form & the

color like as dust.

Probability, the process of washing use water can influence to compounds. There are OH -

ion in water, maybe Al oxide can react with OH-. The produce of this reaction is complex ion.

Al in that complex has 6 ligands. Look at this reaction :

Al2O3(s)   +  2OH-(aq)   +   7H2O(l) → 2[Al(OH)4(H2O)2]-

(aq)

If that complex leaf in open air, it can react again with H2O (from washing) and CO2

(from air). look at this reaction :

2[Al(OH)4(H2O)2]-(aq)  +  H2O(l) + CO2(g) → 2[Al(OH)3(H2O)3](s)   +  CO3

2-(aq)

From that reaction we can know that produce crystal from complex Al. It has 6 ligands too, but

in crystal complex the ligand OH- and H2O is equilibrium. That complex is white fiber like as

trick.

Based on experiment, we can know that Aluminium can react with oxygen. It will

produce white fiber which cover aluminium.

H. Conclusion1. Aluminium and it’s compounds has properties, they are : amphoter, saved by Hg, and

react with oxygen.

2. Al amphoter because it can react with HCl (acid) and NaOH (base). Al more easily react

with base.

3. Al saved by Hg, it show when adding HgCl2, so Al not direct contact with oxygen.

4. Al and it’s compound can react with oxygen, it showed with white fiber in metal

surface.

I. Suggestion1. We must keep dark room from light.2. The sensitive paper must dried actually after diped into mixture solution (FeCl3,

diammonium hydrophosphate, and oxalic acid).3. After use apparatus, it must cleaned.So the chemistry substance is not contaminated.

J. Refference

Achmad, H. 2001. Kimia Unsur dan Radiokimia. Bandung : PT. Citra Aditya Bkti.Keenan, K. 1984. Kimia untuk Universitas. Jakarta : Erlangga.Inorganic Chemistry Lecturer Team. 2015. Manual Work of Inorganic Chemistry Practicum.

Semarang : UNNES.Svehla, G. Vogel. 1985. Analisis Anorganik Kualitatif Makro dan Semimikro. Jakarta : PT.

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