Muskan Shafi Education Content Expert
Education Content Expert
Base is a chemical substance that donates electrons and accepts protons (H+ Ions). Acids and Bases combine together to form Salts.
- Bases release hydroxide ions (OH–) when dissolved in water.
- They are slippery to the touch and bitter in taste.
- They have a pH value of more than 7.
- Bases turn red litmus paper blue and promote specific chemical reactions (Base Catalysis).
- Examples of Bases are Sodium Hydroxide, Calcium Carbonate, Ammonia, etc.
Read More: Importance of pH in Everyday Life
Key Terms: Base, Hydroxide, Ions, Litmus Paper, Neutralization Reaction, Sodium Hydroxide, Acids, Alkalis
What are Bases?
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Bases are any substance that tends to donate electrons, release hydroxide ions (OH– ions), and accept protons (H+ Ions).
- All bases are H+ acceptors when dissolved in water.
- They react with acids to form salt and water.
- Bases turn red litmus paper blue and are slippery in touch.
- They have a pH greater than 7 and have a bitter taste.
- Bases that can be dissolved in water are known as Alkalis.
- Bases can be either strong or weak.
What are Bases?
Read More: NCERT Solutions for Class 10 Science Acids, Bases and Salts
Examples of Bases
Some of the most important Bases in Chemistry are as follows:
- Sodium Hydroxide (NaOH)
- Ammonium Hydroxide (NH4OH)
- Calcium Hydroxide (Ca(OH)2)
- Potassium Oxide (KOH)
- Magnesium Hydroxide (Mg(OH)2)
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Properties of Bases
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Given below are some general properties of Bases:
- Bases turn the color of red litmus to blue.
- They are bitter in taste.
- Bases lose their basicity when mixed with acids.
- Salt and water are formed as a result of the reaction between a Base and an Acid. It is called Neutralization Reaction.
- Bases feel slippery or soapy in touch.
- Some bases are great conductors of electricity.
- Bases like sodium hydroxide, potassium hydroxide, etc. are used as electrolytes.
- Alkalis are bases that produce hydroxyl ions (OH) when mixed with water.
- Strong alkalis are highly corrosive whereas other alkalis are mildly corrosive in nature.
- The pH value of bases ranges from 8-14.
- Hydrogen gas is evolved when metals react with a base.
- Bases are classified on the basis of strength, concentration, and acidity.
- Different types of bases are concentrated base, dilute base, monoacidic base, di-acidic base, and tri-acidic base.
Read More: Acids Bases and Salt Important Questions
Physical Properties of Bases
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Given below are the Physical Properties of Bases:
Bases Taste Bitter
- Bases are quite bitter in taste, and thus, there are very few food materials that are alkaline.
- One must be precautious while tasting bases.
- Tasting bases are considered to be more dangerous than tasting acids.
- It is because of the property of stronger bases for denaturation of proteins.
Bases Denature Protein
- Strong bases that can be dissolved in water easily, such as sodium or potassium lye, are very dangerous.
- It is because a great amount of the structural material of human beings is made of protein.
- Strong Bases can cause serious damage to flesh.
Read More: Acids Bases and Salt Revision Notes
Bases Neutralise Acids in Neutralization Reaction
- Bases react with acids to produce salt and water.
- In this reaction, the acid and base neutralize each other.
- Therefore, these reactions are called neutralization reactions.
- Neutralization Reaction is defined as a reaction between an acid and a base, producing salt and water.
- During neutralization, H+ ions (from acid) and (OH-) ions (from base) combine to produce H2O molecules.
Reactions with Salts
- When a base is heated with an ammonium salt, ammonia gas, another salt, and water are produced.
- For example, heating sodium hydroxide with ammonium chloride, produces sodium chloride, water, and ammonia gas.
- A pungent smell marks the presence of Ammonia Gas.
- Bases react with certain salts to produce another salt and another base.
- For example, when NH4OH is added to a solution of Al2(SO4)3, (NH4)2 SO4 and Al(OH)3 are produced.
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Things to Remember
- Bases are those substances that donate electrons, accept protons, or release hydroxide (OH-) ions.
- They release hydroxide ions (OH-) when combined with water.
- Bases have a pH range from 8-14 and turn red litmus paper to blue.
- They are solid and slippery in nature.
- Sodium Hydroxide, Ammonia, Calcium Carbonate, and Potassium Oxide are some examples of bases.
- Bases combine with Acids to form Salts in a reaction named Neutralization Reaction.
Sample Questions
Ques. List the Properties of Bases. (3 Marks)
Ans. The properties of bases are as follows:
- Bases release hydroxide ions (OH-) when dissolved in water.
- They have a bitter taste and are found less commonly in foods.
- They are soapy or slippery to the touch.
- They turn red litmus blue, while phenolphthalein turns pink.
- Bases react with acids to form salt and water.
- Bases can be strong as well as weak.
Ques. Which reaction takes place upon mixing an acid and a base?
(a) Corrosion
(b) Neutralization
(c) Endothermic Reaction (3 Marks)
Ans. (b) Neutralization
Neutralization is a reaction where salt and water are formed due to the combination of acid and base. There is a combination of H+ ions and OH– ions during the neutralization reaction which forms water.
Acid + Base (Alkali) → Salt + Water
Ques. What are the common uses of bases? (3 Marks)
Ans. Some common uses of Bases are as follows:
- They are used for manufacturing soaps, paper, textiles, and detergents.
- They are also used as a reagent in the laboratory.
- Bases are also used in the preparation of medications.
Ques. What are Antacids? (3 Marks)
Ans. Antacids are weak bases that neutralize the acid in the stomach.
- Antacids utilize two main types of bases called carbonates and hydroxides.
- They neutralize the acid in the stomach by stopping an enzyme that creates acid to break down food for digestion (pepsin).
- They help to relieve symptoms that cause heartburn and indigestion.
Ques. How do Bases react to Indicators? (2 Marks)
Ans. Bases can be detected using two commonly used indicators namely:
- Litmus Paper: Bases turn red litmus paper to blue.
- Phenolphthalein: Phenolphthalein solution turns pink when exposed to bases.
Ques. Why is Sodium Hydroxide called Caustic Soda? (2 Marks)
Ans. Sodium Hydroxide (NaOH) is corrosive towards organic matter and breaks down the skin and flesh proteins to a pasty mass. This is called caustic action. Due to this property of causing a caustic action, due to this property, Sodium Hydroxide is known as caustic soda.
Ques. Are all Bases alkaline in nature? (1 Mark)
Ans. No, all bases are not alkaline in nature. Alkalis are defined as bases that dissolve in water to produce hydroxyl ions (OH-) but not all bases are alkaline. Bases are usually capable of accepting H+ ions.
Ques. What is the pH of 0.05 solution of KOH? (2 Marks)
Ans. KOH is a strong base and dissociates completely into K+ and OH-
pOH = -log (0.05)
pOH = -(-1.3)
pOH = 1.3
pH = 14 - pOH = 14 – 1.3 = 12.7
Ques. State a few examples of Bases and their uses. (3 Marks)
Ans. Given below are some examples of bases along with their uses:
- Sodium Hydroxide (NaOH): It is commonly used in soaps and detergents, along with oven and drain cleaners.
- Calcium Hydroxide (Ca(OH)2): It is used to make cement and lime water. It is also used to neutralize acidic soil.
- Ammonia (NH3): It is used to make a variety of pharmaceutical items and commercial cleaning solutions.
Ques. State the properties of Acids. (3 Marks)
Ans. The important properties of Acids are as follows:
- Acids are sour in taste and are usually sticky in nature.
- Acids have a pH of less than 7.0 and turn blue litmus paper red.
- They react with bases to form salts and facilitate chemical processes and reactions.
- There is a burning sensation when acids come in contact with the skin.
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