Aim: To investigate the chemical properties of the halogens and some of their compounds by using chemical reactions.

It is not found free in nature as it combines readily with nearly all other elements.
Chlorine occurs in nature mainly as common salt (NaCl), carnallite [ KMgCl2.6(H20) ], and sylvite (KCl).
In its liquid and solid form it is a powerful bleaching, oxidizing and disinfecting agent.

• Bromine

General:

States

Energies

Oxidation & Electrons

                                Characteristics:
Pure bromine is diatomic, Br2.
Bromine is the only nonmetallic element that is liquid at ordinary temperatures.
It is a dense, reddish-brown liquid which evaporates easily at room temperature to a red vapor with a strong, chlorine-like odor.
Bromine is less reactive than chlorine or fluorine but more reactive than iodine. It forms compounds with many elements and, like chlorine, acts as a bleaching agent.

• Iodine

General:

States

Energies

Oxidation & Electrons

                                 Characteristics:
Iodine is a bluish-black, lustrous solid. Although it is less reactive than the elements above it in group 17 (fluorine, chlorine and bromine) it still forms compounds with many other elements.
Although iodine is a non-metal, it displays some metallic properties.
When dissolved in chloroform, carbon tetrachloride or carbon disulphide, Iodine yields purple colored solutions. It is barely soluble in water, giving a yellow solution.

*The above information is from Chemical Cool (http://www.chemicool.com/)

Variables:

• Controlled:

The controlled variables will be the following:

1. The initial temperature of the laboratory.
2. The atmospheric pressure of the laboratory.
3. The concentrations of chemical used in the experiment.

• Dependent:

The dependent variables will be the following:

1. The volume of the products.
2. The amount of the products.

• Independent:

The dependent variables will be the following:

1.The volume of the chemicals used.

2.The amount of the chemicals used.

Equipment:

• Test tubes
• Test tube clamp
• Test tube brusher
• Droppers
• Test surface
• Universal indicator
• Universal indicator paper
• Alcohol lamp
• Test tube rack

Reactant:

Concentration:0.1M

• Fresh chlorine water(Cl2)
• Aqueous sodium chlorine(NaCl)
• Aqueous potassium bromide(KBr)
• Aqueous potassium iodide(KI2)

• Diluted hydrochloric acid(HCl)
• Pieces of iodine(I2)
• Aqueous silver nitrate( AgNO3)
• Aqueous lead nitrate(Pb2(NO3))

• Cyclohexane(C6H12)
• I2-KI solution
• Distilled water(H2O)
• Starch solution
• Ethanol(CH3CH2OH)

Method:

Data collection:

*1cm depth of solution in the test tube=1cm3 solution

Part.1: Iodine react with different kinds of reactants.

① I2(s)+H2O(l) →HIO(aq)+HI(aq) 

②

③I2(s)+KI(aq)→KI3(aq)

④CH3CH2OH(aq)+I2(s)→CH3CHO(aq)+HI(aq)

Part.2: Iodine react with starch solution.

Part.3: Test the acid-base properties of halogens

Part.4: Displacements between halogen elements

NaCl(aq) + Cl2(aq) → ×

NaCl(aq)+ I2-KI（aq）→×

2KBr(aq)+Cl2(aq)→2KCl(aq)+Br2(aq)

KBr (aq)+ I2-KI（aq）→×

2KI(aq)+Cl2(aq)→2KCl(aq)+I2(aq)

KI (aq)+ I2-KI（aq）→×

Part.5 Tests for halide ions

• halide ions(Cl-) with silver ions:

NaCl(aq) + HNO3(aq) → NaNO3(aq) + HCl(aq)

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

Part.6: Sublimation of iodine

*Room temperature & ATM (atmospheric pressure).

Conclusion:

Part.1: Iodine react with different kinds of reactants.

• "Like dissolves like" meaning polar things dissolve polar things and non-polar things disolve non-polar things. Because iodine molecule is non-polar, water molecule is a polar molecule, so iodine dissolves very little in water. On the other hand, because ethanol and cyclohexane are non-polar organic solvent, iodine can dissolve in them. KI, which is a polar, ionic compound, will ionize and dissolve in water. When iodine reacts with it, it will form triatomic ion which is very water soluble.
• Halogen molecules are highly soluble in non-polar solvents.

Part.2: Iodine react with starch solution.

• "Iodine solution is used to test for starch; a dark blue color indicates the presence of starch. The details of this reaction are not yet fully known, but it is thought that the iodine (I3− and I5− ions) fit inside the coils of amylose, the charge transfers between the iodine and the starch, and the energy level spacings in the resulting complex correspond to the absorption spectrum in the visible light region. The strength of the resulting blue color depends on the amount of amylose present. Waxy starches with little or no amylose present will color red."

*The above information is from Wikipedia (http://en.wikipedia.org/wiki/Starch)

Part.3: Test the acid-base properties of halogens

• Chlorine water is weak acidic.
• Iodine solution is strong acidic.

Part.4: Displacements between halogen elements

• Reactivity of the halogens decreases going down the group and the more reactive halogen will displace a less reactive halogen from a solution of its ions. This is also a redox reaction.

*The above information is from (http://ibchem.com/IB/ibnotes/brief/per-sl.htm)

• When a halogen atom reacts, it gains an electron to form a singly negative charged ion e.g. Cl + e-  ==> Cl- which has a stable noble gas electron structure like argon. (2.8.7 ==> 2.8.8)
• As you go down the group from one Group 7 halogen element down to the next .. F => Cl => Br => I ...

• the atomic radius gets bigger due to an extra filled electron shell,
• the outer electrons are further and further from the nucleus and are also shielded by the extra full electron shell of negative electron charge,
• therefore the outer electrons are less and less strongly attracted by the positive nucleus as would be any 'incoming' electrons to form a halide ion (or shared to form a covalent bond).

• SO, this combination of factors means to attract an 8th outer electron is more and more difficult as you go down the group, so the element is less reactive as you go down the group, i.e. less 'energetically' able to form the X- halide ion with increase in atomic number.

*The above information is from Doc Brown's Chemistry

(http://www.docbrown.info/page07/ASA2group7a.htm#9.3)

Part.5 Tests for halide ions

• halide ions(Cl-) with silver ions:

*The above information is from (http://ibchem.com/IB/ibnotes/brief/per-sl.htm)

Part.6: Sublimation of iodine

• Vapor pressure has an effect on the point where the sublimation of iodine happens. The vapor pressure of iodine becomes higher when the temperature becomes higher.

Evaluation & Improvement:

• When I was doing the third part of this experiment, because the universal indicator paper was orange initially, it was hard to observe that whatever the colour of it had changed into. In addition, when I compared the colour of indicator paper to the PH colour atla, it was also not easy to decide which colour the reagent belonged to. So next time, I would like not to choose the universal indicator paper which with orange background colour initially to make the observation more accurately.