Transcript Collapsing Can

Preparation of Oxygen
Gas from Bleach
When bleach is treated with a catalyst the rapid
evolution of oxygen gas ensues
Demonstration
 The commercial bleach was a solution of
sodium hypochlorite in water
NaClO(aq)
 When treated with a small amount of
cobalt(II)chloride the hypochlorite
decomposed Catalyst
 2ClO- (aq)
O2(g) + 2Cl-(aq)
 The bubbles given off were the oxygen
gas as concluded from
 Pine splint test
Purpose
 To use a catalyst to decompose
bleach
 To collect the decomposition
product
 To test for the presence of oxygen
gas
Concepts
1.
Decomposition Reactions
2.
Catalysts
3.
Collection and Determination of
Oxygen
1. Decomposition Reactions
 Decomposition reactions are of the
kind
A-B
A
+
B
 In decomposition reactions, a
single substance is converted to
more than one new substance
 In this demonstration hypochlorite
ion decomposes into oxygen gas
and chloride ion
2. Catalysts
 A catalyst is a substance which enables
a chemical change to occur
 A catalyst assists the reactants to
convert to products
 The catalyst itself may be used over and
over: It itself is not changed
 When a catalyst is present it is written
over the reaction arrow
 Addition of a catalyst will speed the rate
of many chemical reactions allowing
them to occur faster than they otherwise
would
3. Collection and Determination
of Oxygen
 Oxygen is a gas and is conveniently
collected by the displacement of water
 A glowing--but not burning--pine splint
will burst into flame if oxygen gas is
present
Conclusions
 Oxygen gas was a decomposition
product of bleach
 A catalyst was used to cause rapid
decomposition
 Oxygen was easily collected
 Oxygen supported combustion
reactions
 with a glowing pine splint
Comments
 This reaction is not only a
decomposition, but also a redox
reaction
 Bleach should NEVER be mixed
with any household chemicals!!!