Year 9 Chemistry – Worksheet 12
3.1 Decomposition and synthesis
Demonstration experiment: Decomposition of iodine pentoxide M
A spatula tip of iodine pentoxide is placed in a test tube, which is fitted with an adsorption tube stopper (to stop harmful gases from escaping).
The following steps are performed:
1. The iodine pentoxide is heated with a Bunsen burner.
2. The test tube is left to cool.
3. The test tube is opened and a glowing splint (piece of wood) is held into it.
4. Ethanol (alcohol) is filled into the test tube and several drops of the resulting solution are mixed with a starch suspension.
O
1. The test tube is filled with a ____________________________, the iodine pentoxide is ___________________________________.
2. After a while ____________________________ is no longer visible. _________________
_________________________ form on the test tube wall.
3. The glowing splint ________________________________ when held into the test tube.
4. When the _____________________ ethanol solution is dripped into the starch suspension it _______________________________________.
Task: Please work together with your neighbor to answer the questions on the back!
C
1. Iodine pentoxide ________________________________ into _________________________:
______________________ (which forms a __________________________________) and _______________________, a ________________________ gas.
2. When cooled the __________________________ ________________________ to form a crystalline solid on the test tube wall. The ______________________ remains
____________________.
3. The glowing splint _______________________________ because of the amount of _______________________ in the test tube.
4. The _________________________ that dissolved in the ethanol ________________ the starch solution ____________________________.
Word equation:
adsorption tube(filled withactivated carbon)
rubber stopper syringe
test tube iodine pentoxide
Year 9 Chemistry – Worksheet 12
Questions to understand the experiment
a) In step two the purple gas that was created in step one disappears while dark crystals form on the test tube wall. State whether this is a chemical or physical change and give reasons.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
b) State the number of substances (apart from the air that filled the test tube to begin with) in the test tube before and after step one. Give reasons.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
BONUS: Explain how the experiment performed proves that iodine pentoxide is a compound.
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
Test reactions
To find out which substances are created in a chemical reaction, chemists have developed tests for many common substances. The practical made use of two of these tests:
Test for oxygen – “glowing splint test”
If a gas contains high amounts of oxygen, it will ____________________ a glowing splint.
Test for iodine/starch
If a solution containing iodine is put in contact with starch (solid or in suspension),
___________________________________ will be visible. This can be used to test for either substance (using the other to perform the test).
