Bleach (1/4)
Bleach
-chlorine bleach
-sulphur dioxide bleach
A)Chlorine Bleach
i)to clean and bleach fabrics
ii)to kill germs ( used as ______)
Production of Chlorine Bleach
It is made by dissolving chlorine gas in a solution sodium hydroxide.
Or
Bleaching powder is made by passing chlorine over moist calcium hydroxide.
Both bleaching solution and bleaching powder contain ______ion (OCl-) as the active ingredient.
B)Laboratory Preparation of Chlorine Bleach
It is prepared during the electrolysis of brine ( a concentrated solution of sodium chloride ). During electrolysis, three products are formed:
- ______gas at the anode
- ______gas at the cathode
- ______solution in the cell.
C)Industrial Manufacture of Chlorine Bleach
1) Flowing mercury cell
At anode (______):
At cathode (______):
Sodium dissolves in mercury to form an alloy. It flows into a second cell where it reacts with water to form ______and ______solution.
Mercury is then recovered and recirculated.
2) Diaphragm cell
The electrode compartments are separated by a ______diaphragm. Ions can pass slowly through this diaphragm, but gas molecules cannot.
At anode:
At cathode:
The hydroxide ions are prevented from reacting with the chlorine gas by the ______. A solution of sodium hydroxide and unchanged sodium chloride is formed in the cathode compartment.
3) Membrane cell
A plastic membrane is used to separate the anode compartment from cathode compartment. This membrane allows only ______ions to pass through.
D)Preparation and Properties of Chlorine
Chlorine is conveniently obtained from a chlorine bleach by the action of a dilute ______.
Properties of Chlorine
- colour: ______
- denser than air
- has a characteristic pungent, choking smell
- is ______.
- is slightly soluble in water, forming a pale greenish-yellow solution called ______
- turns moist blue litmus paper ______.
- is an ______agent.
Chlorine Water
When chlorine dissolves in water, it reacts reversibly to form hydrochloric acid and ______.
Thus chlorine water contains dissolved chlorine, water, hydrochloric acid and hypochlorous acid and it has a smell of chlorine. Chlorine water is often used instead of chlorine gas in some experiment as it would be safer and more convenient to be used.
Oxidizing Properties
When chlorine water is added to a solution of potassium bromide, the colourless solution changes to ______.
When chlorine water is added to a solution of potassium iodide, the colourless solution changes to ______.
In these two reactions, the more reactive halogen, chlorine, displaces bromide ions and iodide ions from the solutions. Thus, these reactions are examples of ______.
E)Comparison of Chlorine Bleach and Sulphur Dioxide Bleach
Chlorine Bleach / Sulphur Dioxide BleachInvolves the hypochlorite ion / Involves the sulphite ion
Bleach by ______/ Bleach by ______
Bleaching action is ______and more ______/ Bleaching is ______and ______
Bleaching action can last for a ______time / Bleaching action is not permanent and original colour will slowly be ______.
Used with cotton, linen, some food stains / Used with wool, silk, paper, some foods
F)Properties of Sulphur Dioxide and Sulphite
In the presence of water, sulphur dioxide is a good ______agent. It can be oxidized to form ______.
e.g. 1. reaction with bromine water
e.g. 2. reaction with acidified potassium dichromate solution
e.g. 3. reaction with acidified potassium permanganate solution