Bases

A base is defined as any substance which releases hydroxyl ions (OH-) when dissolved in water. Bases which are soluble in water are called alkalies. This note about bases provides information about bases its properties and common uses.

Summary

A base is defined as any substance which releases hydroxyl ions (OH-) when dissolved in water. Bases which are soluble in water are called alkalies. This note about bases provides information about bases its properties and common uses.

Things to Remember

  • A base is defined as any substance which releases hydroxyl ions (OH-) when dissolved in water. Sodium hydroxide and ammonia are bases because they give hydroxyl ions in water.
  • Bases which are soluble in water are called alkalies.
  • All alkalies are bases but all bases are not alkalies.
  • Physical properties of bases include its soapy touch, bitter taste etc.

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Bases

Bases

A base is defined as any substance which releases hydroxyl ions (OH-) when dissolved in water. Sodium hydroxide and ammonia are bases because they give hydroxyl ions in water.

NaOH → Na+ + OH-

Sodium hydroxide

NH3 + H2O → NH4+ + OH-

Ammonia (Ammonium ion)

Bases which are soluble in water are called alkalies. Some bases are not soluble in water. They are not alkalies. Thus, all alkalies are bases but all bases are not alkalies. Sodium oxide is called soda and potassium hydroxide is called caustic potash.

Some are given below:

S.N Bases Formula
1. Sodium hydroxide NaOH
2. Potassium hydroxide KOH
3. Aluminum hydroxide Al(OH)3
4. Ammonium hydroxide NH4OH
5. Sodium oxide Na2O
6. Potassium oxide K2O
7. Magnesium oxide MgO

Properties of bases

Physical properties:

  1. They are soapy in touch.
  2. They have a bitter test.
  3. They turn red litmus paper into blue.
  4. They turn turmeric paper brown.
  5. They turn methyl orange yellow and phenolphthalein pink.

Chemical properties:

  1. They produce hydroxyl ions (OH-) in aqueous solution.
  2. They neutralize acids to form salt and water.
    KOH + HCl → KCl + H2O
    Potassium hydroxide + Hydrochloric acid → Potassium chloride + Water
  3. Bases react with carbon dioxide to form carbonate
    K2O + CO2 → K2CO3
  4. They react with metals of the type zinc and aluminum and produce hydrogen.
    Zn + 2NaOH → NaZnO2 + H2
  5. When a base is heated with an ammonium salt, ammonia gas is given off. It can recognized by its extremely pungent smell.
    NaOH + NH4Cl → NaCl + H2O + NH3
    Sodium hydroxide + Ammonium chloride → Sodium chloride + Water + Ammonia

Some bases which are commonly used in daily life are:

S.N Bases Uses
1. Sodium hydroxide In the manufacture of soap.
2. Potassium hydroxide Firewood ash-filtered wood ash is used for washing clothes in rural areas.
3. Aluminum hydroxide As medicine (antacid) for gastric patients.

Differences between acids and bases:

S.N Acids Bases
1. Turn blue litmus into red. Turn red litmus into blue.
2. React with metals to give the salt and hydrogen gas. Normally do not react with metals. Only some metals like zinc, aluminum and tin react to give hydrogen.
3. Are corrosive to skin. Are slipper to touch.
4. Are sour in taste. Are bitter in taste.
5. React with bases to give salts and water. React with acids to give salt and water.
6. An aqueous solutions of acids contain replaceable hydrogen ions. An aqueous solution of the base contains replicable hydroxyl ions.
7. Give no color with phenolphthalein. Give red color with phenolphthalein.

Lesson

Acid, Base and Salt

Subject

Science

Grade

Grade 8

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