Experiment 10: Hidden
Water
date | aim | method
| materials & equipment | results
| conclusion
Date
16 February 2010 by Quest 2, to link in with Chapter
10 of our book.
Aim
To observe colour changed when water is driven out of copper sulphate
and cobalt chloride crystals, and when water is reabsorbed
into the crystals.
Method
Add a small amount of each type of crystals to its own test tube and
gently heat over meths burner until no further change is evident. Add
water dropwise to each sample until no further change is evident.
Materials & Equipment
- Copper sulphate, CuSO4•5H2O.
- Cobalt chloride, CoCl2•6H2O.
- Water.
- Test tubes.
- Meths burner.
- Metal spatula.
- Beaker (actually a drinking glass).
- Pipette.
Results/Observations
| Chemical |
Test |
Observations |
| Copper sulphate |
Initial state |
|
| Dehydrating |
- Sizzling noise upon initial heating.
- Shortly after the crystals started to go white around the edges
of the pile.
- Condensation on the inside of the top half of test tube.
- Eventually all the crystals turned a very pale green-grey colour.
|
| Rehydrating |
- When water was dropped in there was a sizzling noise.
- Condensation formed on the inside of the top of the test tube.
- The sample turned blue again.
- When more water was added the sample dissolved to make blue
water.
|
| Cobalt chloride |
Initial state |
- Initially deep red/purple crystals.
- Crystals are large, dark in some places and light in other places,
and "look rather wet".
|
| Dehydrating |
- Sizzling noise upon initial heating.
- Condensation on the inside of upper half of test tube.
- Looked like it melted and changed to a deep blue colour.
- Changed to purple.
- Changed to light blue/faded blue.
- Light blue spattering on inside of test tube.
- Mid blue colour and looks quite dry.
- Black around edge.
- Turning into a fern shape with a dry paste look.
|
| Rehydrating |
- Water was added more quickly than desired (not dropwise).
- Sizzling noise as water added.
- Opaque purplish brown liquid.
|
Conclusion
- Water was driven off both samples upon heating.
- Water was absorbed by both dehydrated samples.
- The samples were probably still quite hot when the water was added.
- John needs practice adding water dropwise.
|
