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Me03 Alkali metals 3: Differences in reactivity with water
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(For
experienced chemistry teachers only!
*
Left:
Cut TINY (1 x 1
x 0,2 mm) pieces of lithium, sodium and potassium from cleaned and dry
metal lumps.
*
On a porcellain saucer connect 5 drops to have one big water drop.
* Place the Li the metal
beside it, use a wire to push it into the water drop. Clean the lump, dry
it carefully.
* Repeat the experiment
with sodium and finaly with potassium
* Observations:
Li,
Na, K react with water, gas bubbles are released, the metals disappears.
* Photo 2:
Na reacts more vigorously than Li: It melts, a silvery ball is formed running
on the water.
*
Photo
3: K is most reactive: It catches fires as soon
as it comes into contact with water.
* right:Explanation
with the element pyramid:
Li,
Na,
K
are the first members of the element family 1 (Alkali metals):
During
their chemical reaction with water each these alkali atom gives 1 electron
to a water molecule.
The metal atoms are oxidized
(their positive ions have as may electrons as He,
Ne,
Ar
atoms).
In the same moment each
water molecule is reduced. A hydroxide
ion (OH-) and a H atom are left.