Discovery of the alkali metals: a WORKSHEET
How Davy found sodium.(October 1807 - at the Royal Institute)
Davy obtained sodium by melting some sodium
hydroxide in a platinum crucible. He connected
the:
 positive end of thebattery to the metal
crucible.
 negative end of the battery to the platinum
wire.
He managed to melt the sodium hydroxide by
blasting oxygen over a spirit burner (to get the
flame hot).
Once electricity flowed through the crucible:
oxygen gas was given off at the anode
sodium
hydrogen were given off at the cathode.
Small globules of molten sodium rose through
the caustic soda and caught on fire on reaching
the air, burning with a yellow flame.
What Davy found out about potassium and sodium
1) Physical Properties
Property
good conductor
good conductor
shiny when
of heat
of electricity
cut
potassium
yes
yes
yes
sodium
yes
yes
yes
To Davy these 3 properties suggested that he had indeed found 2 new metals but he was
troubled by the fact that both elements floated on water an unusual property of metals !!
1) Chemical properties
(a) Reaction with water
Davy managed to carry out 3 experiments

Reaction of metals with water

Reaction of metals on filter paper with water

Reaction of metals with ice.
In each case he used turmeric as an indicator - this changes colour in either acid or alkali.
However, we are going to use the indicator phenolphthalein
(i)
Reaction of metals sodium and potassium with water
(i) Reaction of metals with water
Description -write down what happens
(i) With sodium
(ii) With potassium
(ii)
Reaction of metals sodium and potassium (on filter paper) with water
(ii) Reaction of metals (on filter paper)
with water
Description -write down what happens
(i) With sodium
(ii) With potassium
(iii)
Reaction of sodium and potassium with ice
(iii) Reaction with ice
Description -write down what happens
(i) With sodium
(ii) With potassium
CONCLUSION : REACTIONS WITH WATER
In each case the indicator turned........................................................... indicating that an
................................... was formed. A colourless gas ................................which burned with a
squeaky was also given off.
From this information Davy suggested that
sodium
+
water
sodium oxide
+
hydrogen
potassium
+
water
potassium oxide
+
hydrogen
(b) Reaction with oxygen
Davy took both metals and heated them in oxygen.
Today we make the oxygen by reacting manganese dioxide with hydrogen peroxide (H2O2).
In this reaction oxygen is made when hydrogen peroxide is decomposed by the manganese
dioxide which acts as a catalyst.
decomposes
Hydrogen peroxide
oxygen
H2O2
O2
+
water
H2O
(iii) Reaction of sodium and potassium with oxygen
Reaction of with oxygen
Description -write down what happens
(i) With sodium
(ii) With potassium
Complete the word equations
sodium
+
oxygen
.................................................................
potassium
+
oxygen
.................................................................
Apart from these reactions Davy reacted sodium and potassium with sulphuric acid and
alcohol. In each case he found that the metal grabs oxygen forming the metal oxide.
NAME.............................................................................
CLASS......................
HOMEWORK: ALKALI METALS
In 1860 and 1861 the metals Caesium and Rubidium were discovered.
These have similiar reactions with water and oxygen .
Find out using the CHEM
SCHOOL CD ROM what happens when
(a) Rubidium is put into water - describe the video clip
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
Equation
Rubidium
+
water
...............................+..................................
(b) Caesium is put into water - describe the video clip
............................................................................................................................................
............................................................................................................................................
............................................................................................................................................
Equation
Caesium
+
water
...............................+..................................