What is formed when group 1 alkali metals like lithium, sodium or potassium react with water?
The reaction with water is very exothermic, fast and violent. If a lump of lithium, sodium or potassium is placed in cold water, the metal floats, it may melt and move around the surface of the water with ‘fizzing’. Note that these alkali metals float on water because of their low density. If universal indicator is added, it changes from green (pH 7) to purple (pH 13-14), showing an alkaline metal hydroxide was formed. The formation of an alkali with water is why they are called Alkali Metals. The colourless gas hydrogen is also given off and pops with lit splint – but this is not the best of experiments to collect it from! The more reactive the metal, the more vigorous the reaction. Lithium and sodium do not normally cause a flame but the potassium reaction is exothermic enough to ignite the hydrogen. 2H2(g) + O2(g) => 2H2O(l) The hydrogen flame turns lilac due to hot potassium atoms in it. Note: in flame tests hot lithium atoms give a crimson colour and sodium a yellow colour (more d
