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Bases taste bitter. But we cannot taste the liquid as it is dangerous thing to do since it can rapidly burn the skin. They neutralise acids. If we touch them, they have a soapy feel. Bases turn red litmus paper blue. Most bases are not much soluble in water. But, some bases are highly soluble in water. These are given a special name - alkalis.
Strong and Weak Bases
A base which completely ionizes in water and thus produces a large amount of hydroxide ions (OH-) ions is called a strong base.
Eg: sodium hydroxide and potassium hydroxide are strong bases.
Hydroxides like ammonium hydroxide, aluminium hydroxide, calcium hydoxide, etc., are weak bases because they partially ionize in water and produce only a small amount of hydroxide ion.
When a piece of magnesium ribbon is burnt, it burns with a bright light and a white powder of magnesium oxide is formed. This powder is dissolved in water and forms magnesium hydroxide, which is a base. It turns red litmus to blue and also it is also soapy to touch. Similarly, the other metals like sodium, potassium and calcium combine with oxygen to form corresponding basic oxides. These oxides dissolve in water forming corresponding hydroxides.
2Mg + O2  2MgO (Magnesium Oxide)
MgO + H2O Mg(OH)2 (Magnesium Hydroxide)
2Ca + O2 2CaO (Calcium Oxide)
CaO + H2O Ca(OH)2 (Calcium Hydroxide)


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