C3.10 Properties of alkali and other metals
The alkali metals have low melting
points low densities and are soft compared to other
metals.
For example lithium has a melting point of 180ºC and
caesium has a
melting point of just 29ºC. These are low compared
to other typical metals such as iron, melting point 1500ºC.
Sodium and potassium are soft
and can be cut with a knife but iron is hard.
Task C3.10
C3.11 Alkali metals and water
When an alkali metal is put into water, it reacts very
vigorously. It moves around the surface fizzing. Hydrogen is produced which
can be tested using a lighted splint. The metal also gets hot and potassium
gets hot enough to ignite in its own heat. The water turns into a hydroxide.
Reactivity increases as you go down the group.
2Na(s) + 2H2O(l) ---- 2NaOH (aq) + H2(g)
| metal | observations | reactivity |
| lithium | fizzes gently moving slowly | reactive |
| sodium | fizzes vigorously, moves quickly | very reactive |
| potassium | violent fizzing, bursts into lilac flame | violently reactive |
Task C3.11
C3.12 Properties of alkali metal compounds
Alkali metal compounds are all white solids which are soluble in water.
| compound | solubility | type of metal |
| sodium carbonate | soluble | alkali metal |
| lithium chloride | soluble | alkali metal |
| potassium sulphate | soluble | alkali metal |
| calcium sulphate | insoluble | group 2 metal |
| copper carbonate | insoluble | transition metal |
Alkali metal hydroxides or oxides dissolve in water and are
alkalis. An alkali has a pH of over 7, e.g. 14. An alkali turns universal
indicator purple. An alkali can neutralise an acid. Whenever
an acid is neutralised it produces water and a salt.
sodium hydroxide + hydrochloric acid ---> sodium chloride + water
(an
alkali)
(a salt)
NaOH(aq) + HCl(aq) ---> NaCl(aq) + H2O(l)