IGCSE CHEMISTRY FREE NOTES Alkali metals

Properties of alkali and other metalsThe 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.

Alkali metals and waterWhen 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

Reactivity of metal with water

lithium
fizzes gently moving slowly
reactive


sodium
fizzes vigorously, moves quickly
very reactive


potassium
violent fizzing, bursts into lilac flame
violently reactive

Properties of alkali metal compoundsAlkali metal compounds are all white solids which are soluble in water.
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 (a salt)


NaOH(aq) + HCl(aq) ---> NaCl(aq) + H2O(l)