Practical 4 Halogens

PRACTICAL 4 TOPIC : REACTION OF HALOGENS WITH WATER AND SODIUM HYDROXIDE

NAME: NUR ARIFAH BT MOHD SABRI MATRIX NO: DPM0010_2013B PROGRAMME: DIPLOMA IN PHARMACY BATCH APRIL 2013 SEMESTER : 1 DATE : 12 JUNE 2013 LECTURER’S NAME : MADAM ARIESMA RAZANA

OBJECTIVE : To determine the reaction of halogens with water and sodium hydroxide. INTRODUCTION : The Halogens are typical non–metals and form the 7th Group in the Periodic Table . 'Halogens' means 'salt formers' and the most common compound is sodium chloride which is found from natural evaporation as huge deposits of 'rock salt' or the even more abundant 'sea salt' in the seas and oceans. The halogen dissociates in water to form it is respective acid or acids. In sodium hydroxide, since all halogens are above hydroxides in the electronegative series, they displace the hydroxide to form the sodiumhalide.

MATERIALS AND APPARATUS :

1. Liquid bromine

2. Liquid chlorine

3. Iodine crystals

4. Distilled water

5. pH paper

6. Dilute sodium hydroxide (0.1M)

7. Test tubes (6 pieces per group)

8. Dropper

9. Test tube rack

10. 5ml measuring cylinder

PROCEDURE :

Part A – reaction of halogens with water

I.) With chlorine

1. 5ml of distilled water is poured into a clean test tube. A few drops of liquid chlorine are added into this test tube.

2. The solution is then tested with pH paper. All observations are recorded.

II.) With bromine

1. 5ml of distilled water is poured into a clean test tube. A few drops of liquid bromine are added into this test tube.

2. The solution is then tested with pH paper. All observations are recorded.

III.) With iodine

1. 5ml of distilled water is poured into a clean test tube. A small iodine crystal is added into this test tube.

2. The test tube is then closed with a stopper and shaken well.

3. The solution is then tested with pH paper. All observations are recorded.

Part B – reaction of halogens with sodium hydroxide

I.) Chlorine and sodium hydroxide

1. 5ml of dilute sodium hydroxide is poured into a clean test tube. A few drops of liquid chlorine are added into this test tube.

2. The test tube is then closed with a stopper and shaken well.

3. All observations are recorded.

II.) Bromine and sodium hydroxide

1. 5ml of dilute sodium hydroxide is poured into a clean test tube. A few drops of liquid bromine are added into this test tube.

2. The test tube is then closed with a stopper and shaken well.

3. All observations are recorded.

III.) Iodine and sodium hydroxide

1. 5ml of dilute sodium hydroxide is poured into a clean test tube. A small iodine crystal is added into this test tube.

2. The test tube is then closed with a stopper and shaken well.

3. All observations are recorded.

RESULTS HALOGEN

CHLORINE BROMINE IODINE

OBSERVATION REACTION WITH WATER REATION WITH SODIUM HYDROXIDE YELLOW TO BLUE BLUE NOT CHANGE BLUE NOT CHANGE BLUE

DISCUSSIONS

i)

Halogens react with water to form acid. For example :

Chlorine reacts with water to form hydrochloric acid and hypochlorous acid, a solution that can be used as a disinfectant or bleach:

Cl2 + H2O ->HCl + HClO

Bromine slowly reacts with water to form hydrogen bromide and hypobromous acid.

Br2 + H2O ->HBr + HBrO

Iodine reacts slightly with water to form hydrogen iodide and hypoiodous acid.

I2 + H2O -> HI + HIO

The reaction between iodine and water and between bromine and water does not give any changes to the pH paper because the reaction is too slow.

ii)

Halogens react with sodium hydroxide to form salt and water.

Chlorine reacts with sodium hydroxide to form sodium chlorate and water. Cl2 + 2NaOH ->NaCl + NaOCl + H2O

Bromine reacts with sodium hydroxide to form sodium bromide and water. Br2 + 2NaOH ->NaBr + NaBrO +H2O

Iodine reacts with sodium hydroxide to form sodium iodide and water. 6NaOH + 3I2 ->5NaI + NaIO3 + 3H2O

QUESTIONS 1. HALOGEN REACTION WITH WATER CHLORINE

Cl2 + H2O -> HCLO + HCl

BROMINE

Br2 + H2O ->HBrO + HBr

IODINE

I2 + H2O -> HIO + HI

REATION WITH SODIUM HYDROXIDE Cl2 + 2NaOH ----- NaCl + NaOCl + H2O Br2 + 2NaOH = NaBr + NaBrO +H2O 3I2 + 6NaOH= 5NaI + NaIO3 + 3H2O

2. There are two properties of halogen other than those observed in this experiment . First, halogen have high effective nuclear charge, therefore they are highly electronegative. They gain an electron through reaction with other elements. Next, halogens are highly reactive, and will combine directly with almost all elements. Due to this high level of reactivity, the halogens are almost never found in pure form; rather, they have to be extracted. 3. The reactivity of halogens based on the periodic table: The halogen elements have seven valence electrons,they only require one additional electron to form a full octet. This characteristic makes them more reactive than other non-metal groups. Halogens are one electron short in the outermost (p) shell, adding an electron creates a stable configuration, hence releases energy. The further you go up the halogen series (i.e. bromine->flourine) the closer the outer orbit is to the nucleus, hence the greater the attraction and hence the higher the electronegativity of the halogen.

PRECAUTIONS : •Always ensure that you wear proper fitting clothes and nothing that is too loose. You should also wear your lab coat to avoid spilling anything on your clothes.

•Make sure you read the bottle labels carefully and only use what you are supposed to use during an experiment. You should not try out anything on your own unless you are very sure of what reagents or chemicals you need to use and their results

•Use rubber stopper to seal the mouth of the test tube.

•Make sure that the the test tube is in a clean and dry condition before using it.

•Place the eyes perpendicularly to the scale of graduated cylinder during the measuring of distilled water, sodium hydroxide, chlorine and bromine to avoid parallax error.

CONCLUSION : When chlorine react with water , the pH paper turns from yellow to blue. There are no change when bromine and iodine react with water. When chlorine, bromine and iodine react with sodium hydroxide, pH paper turns from yellow to blue.

REFERENCES : 1. 2. 3. 4.

http://www.docbrown.info/page03/The_Halogens.htm http://wiki.answers.com/Q/Reaction_of_halogen_with_water_and_sodium_hydroxide http://wiki.answers.com/Q/What_is_the_Equation_for_chlorine_water Chemistry for matriculation forth edition semester 1