Describe the reactions of the alkali metals and alkaline earth metals. Identify the conditions needed for corrosion of metals.
Organise metals according to how reactive they are with water and dilute acid.
Reaction of Metals with Water
When metals react with water, the products formed are a metal oxide or metal hydroxide and hydrogen gas.
z Fig. 14.2.1
Sodium catching fire when reacted with water
Alkaline earth metals
Group 2 metals are known as the alkaline earth metals because an old name for oxide was ‘earth’ and their oxides are alkaline.
When alkali metals (such as sodium) react with water, the metal floats on the surface of the water. Hydrogen gas is released and a sodium hydroxide solution is formed. This is an alkaline solution (it will turn red litmus indicator blue and has a pH greater than 7).
The word equation for this reaction is: Sodium + water → sodium hydroxide + hydrogen
Sodium reacts faster with water than lithium. Sodium may even catch fire during the reaction. Potassium is even more reactive with water than sodium is.
Similar to the alkali metals, alkaline earth metals become more reactive as you go down group 2 on the periodic table.
Reaction of Metals with Oxygen
Sodium and potassium are shiny when freshly cut but dull almost immediately when they react with oxygen in the air.
When metals react with oxygen, the product formed is a metal oxide. For example:
Magnesium + oxygen → magnesium oxide
The oxides of sodium and potassium are dull in colour. The oxide of magnesium is white. The oxide of iron is red.
Magnesium oxide is formed in the laboratory using the method shown in Fig. 14.2.3:
z z 240 240
Fig. 14.2.2 Freshly cut sodium
Gas jar
Magnesium ribbon
Fig. 14.2.3
Reaction between magnesium and oxygen to produce magnesium oxide
