Do you know about any compound which reduces the acidity of soil? Are you thinking about calcium hydroxide or calcium oxide? Do you know what are they? In this lesson you will learn about the bases and alkalis which neutralizes the effect of acids.
What is a base?
Base is metal oxide or metal hydroxide that reacts with acid to produce salt and water. For example;
calcium hydroxide + hydrochloric acid →calcium chloride + water
In this equation, calcium hydroxide is a soluble base (alkali).
Let's have a look of some bases which are used in our everyday life:
Magnesium oxide is used in medicines which cure gastric pain. Ammonia solution is used in fertilizers.
Most bases are insoluble in water but those which are soluble are called Alkalis.
What is an Alkali?
Soluble bases are termed as Alkali. An Alkali is a metal hydroxide that releases hydroxide ions (OH-) in aqueous solution.
Sodium oxide + water → sodium hydroxide
Properties of Alkalis
Alkalis have a bitter taste and are slippery/ soapy.
They turn red litmus paper blue.
They react with acids to form salt and water.
They react with ammonium salts to produce salt, water and ammonia.
Alkali + Ammonium salt → salt + water+ ammonia
For example;
Potassium hydroxide + ammonium sulfate → potassium sulfate + water + ammonia
Alkali react with solution of one metal salt to give another metal salt and metal hydroxide
Alkali + salt → salt + metal hydroxide
For example;
Ammonium hydroxide + iron sulfate → ammonium sulfate + iron hydroxide
Types of oxides
Oxides are the compounds of metal and oxygen for example carbon dioxide, magnesium oxide, sulfur dioxide and lead oxide. There are four different types of oxides discussed below;
1. Acidic oxides
They're made up of non metals. They're soluble in water for example sulfur dioxide and when they dissolve in water, they form acids.
Sulfur dioxide + water → sulfurous acid
They don't react with acids. They react with bases to form salt and water.
Sulfur dioxide + sodium hydroxide → sulfur sulfite + water
Why is silicon dioxide an acidic oxide?
Silicon dioxide is insoluble in water but reacts with bases to form salt and water.
2. Basic oxide
They're oxides which are mostly metals. They're insoluble in water however, few like sodium oxide and lithium oxide are soluble (to form alkalis). They're solids at room temperature. They react with acids to form salt and water, but don't react with bases.
Sodium oxide + sulfuric acid → sodium sulfate + water
3. Amphoteric oxide
They are metallic oxides that can behave like both acids and bases. One of their examples is zinc oxide.
Zinc oxide + sodium hydroxide → sodium zincate + water
Zinc oxide + hydrochloric acid → zinc chloride + water
They can react with both acids and bases. In the first reaction, zinc oxide acts as an acidic oxide and in second reaction, zinc oxide acts as a basic oxide. One more example is aluminum oxide. Also, they're insoluble in water.
4. Neutral oxide
Neutral oxide are the oxides of non-metals which are insoluble in water except of H2O itself. Some of the examples of neutral oxides are carbon monoxide and nitric oxide.
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