Weak Base – Meaning, Definition, Properties, and Examples

You may have learnt about sour and bitter substances. These tastes are due to acids and bases in food items. Sometimes you may have heard a member of your family or neighbours saying that they are facing acidity issues because of overeating.

To treat their situation, some people suggest home remedies such as juices, vinegar, lemon water, baking soda solution, etc., but have you wondered why these remedies help the person with his acidity problems? Which property do you think of when selecting these remedies? These remedies include bases. As you know, in Chemistry, bases are classified into different categories. They can be strong and weak.

This article is about base substances and their properties, getting the answer to what is a weak acid and weak base, weak base examples, and many other questions related to base substances.

What Is a Weak Base?

Some substances, when you taste them, feel bitter. Generally, they are called bases or alkalis. In Chemistry, substances that release OH– ions when dissolved in water are called the base.

There are some more weak base definition for the bases. Some of them are

• Molecules or ions that can accept H+ (or hydrogen) ions and form acids are called bases.
• A substance that tastes bitter and feels slippery on touching bases.
• Those chemicals that convert red litmus solution (or paper) into blue are called bases.

Now, the question is, what are a weak base and a strong base? And how do you differentiate them? Let’s dive into these questions. In answering what a weak base is, it can be described as a substance that, when dissolved in water, does not break completely into its constituent ions.

Weak bases have some other properties, such as their solutions being poor conductors of electricity. They are also categorised as weak electrolytes. In contrast to weak bases, strong bases dissociate completely in their aqueous state. They are good or upright conductors of electricity and are also known as strong electrolytes.

What Is a Weak Base in Terms of Equilibrium?

The weak base ions do not completely dissociate in the aqueous solution. During the ionisation of a weak base, a chemical equilibrium takes place. This equilibrium state establishes between the concentration of the undissociated base and its constituent ions. Remember that a poor base’s conjugate acid is always a poor one. In the same way, the conjugate base of a poor acid also acts as a poor base.

When you dissolve a weak base in water, the equilibrium arises, given as:

• B + H2O ⇌ BH+ + OH– (B is for any weak base)

In this equilibrium reaction, an electron pair on the basic molecule accepts a proton H+ From the water molecule. As a result, the formation of a hydroxide ion (OH–) takes place. As the concentration of the reactant increases, the equilibrium will shift towards the right side, and base ions start to form. The higher the reactants’ concentration, the weaker the base form. Similarly, the greater the concentration towards the right side of the equilibrium, the stronger the base.

Some Examples of Weak Bases and Strong Bases Used in Daily Life

Several weak base examples and strong base examples that you have used in your daily life, whether knowingly or unknowingly.

• Weak bases:– Magnesium hydroxide as antacids, ammonia as a rocket fuel, aluminium hydroxide as a deodorant, etc.
• Strong bases:- Alkaline batteries, lubricating grease, soap, baking soda, etc.

Pure water can act as a poor base and a poor acid. Some other common examples of bases are Vegetables and fruits, such as watermelon, kiwi, etc.

Classification of Bases

Bases are also classified into different categories based on their concentration, strength, and acidity.

1. Classification of Bases Based on Their Concentration:

• Concentrated Base: If in a solution form, the concentration or percentage of the base is higher than the solvent they are dissolved in, the base solution is termed the concentrated base solution.

• Dilute Base: If in a solution form, the concentration or percentage of the base is lower than the solvent they are dissolved in, the base solution is termed the diluted base solution.

2. Classification of Bases Based on Their Strength:

• Strong base: If the aqueous solution of the base is completely ionised or the bonds between the ions in a base molecule are completely released, the base solution is termed a strong base.

• Weak base: If the aqueous solution of the base is incompletely ionised or the bonds between the ions in a base molecule are not completely released, the base solution is termed a weak base.

3. Classification of Bases Based on Their Acidity with Examples

• Monoacidic base: If one hydroxyl ion reacts with only one hydrogen ion in an electrolyte solution, the base formed is termed a monoacidic base. For instance, NaOH, etc.

• Diacidic base: If in an electrolyte solution, two hydroxyl ions react with two hydrogen ions, the base formed is termed a diacidic base. For instance, Ca(OH)2, etc.

• Triacidic base: If three hydroxyl ions react with three hydrogen ions in an electrolyte solution, the base formed is called a triacidic base. For instance, Fe(OH)3, etc.

List of Weak Bases and Acids 

Depending upon the classification of bases, the list below gives weak base examples.

• Ammonia (NH3)
• Lead hydroxide (Pb(OH)2)
• Aluminium hydroxide (Al(OH)3)
• Copper hydroxide (Cu(OH)2)
• Ferric hydroxide (Fe(OH)3)
• Trimethylamine (N(CH3)3)
• Zinc hydroxide (Zn(OH)2)
• Aniline (C6H5NH2)
• Methylamine (CH3NH2)
• Pyridine( C5H5N)

Uses of Weak Bases in Daily Life

You have used many bases in your daily life for various purposes. Some of these bases and their uses are given below:

Sodium Hydroxide, NaOH (Strong Base – Comparison)

It is used to manufacture soaps, textiles, paper, and detergents, refine petroleum, and unblock the home’s drains. It is also helpful as a soda solution.

Calcium Hydroxide, Ca(OH)₂ (Strong Base)

One of the products of this base is lime water. It is used to prepare dry mixes for painting and decorating, manufacture bleaching powder, and neutralise soil acidity. It is one of the chief ingredients in whitewash and mortar.

Magnesium Hydroxide, Mg(OH)₂ (Mild Base)

It is commonly used in producing laxatives, gastritis drugs (ulcer drugs), and toothpaste.

Urea, H₂NCONH₂ (Weak Base)

It is used in the production of chemical fertilisers.

Ammonium Hydroxide, NH₄OH (Weak Base)

It is used to manufacture fertilisers, plastics, rayon, and dyes and as a chemical reagent.

Properties of Weak Bases

Name of the Base	Chemical Formula	Molar Mass	Density	Melting Point
Aluminium hydroxide	Al(OH)3	78 g/mol	2.42 kg/m3	300℃
Lead hydroxide	Pb(OH)2	241.21 g/mol	7.41 g/cm3	135℃
Ferric hydroxide	Fe(OH)₃	106.867 g/mol	4.25 g/cm3	135℃
Copper hydroxide	Cu(OH)2	97.561 g/mol	3.37 g/cm3	80℃
Zinc hydroxide	Zn(OH)2	99.424 g/mol	3.05 g/cm3	125℃
Trimethylamine	N(CH3)3	59.11 g/mol	670 kg/m3	-117.20℃
Aniline	C6H5NH2	59.11 g/mol	1.02 g/cm3	-6℃
Pyridine	C5H5N	79.1 g/mol	982 kg/m3	-41.6℃
Lithium hydroxide	LiOH	23.95 g/mol	1.46g/cm3	462℃

Ammonia as a Weak Base

Ammonia, NH3, is an organic compound covalently bonded with hydrogen atoms forming a tetrahedral geometry. Ammonia’s weak base is easily recognised due to its pungent smell. Under normal temperature and pressure, it exists as a colourless gas.

Applications:

Ammonia weak base is commonly used to produce urea fertiliser mixtures, medicines, rocket fuels, battery manufacture, fuel, explosive materials, plastic, paper, and household appliance cleaners.

Physical Properties of Ammonia

Ammonia’s weak base occurs naturally in the environment, such as soil, air, plants, water, and animals. It has a boiling point of -33.34℃ and a melting point of -77.73℃. The molar mass of ammonia is 17.031 g/mol and has a density of 0.73 kg/m3.

Weak Base vs Strong Base

You can see the work of a base when you put an antacid pill in water to make your stomach feel not so sour. Not every base functions in the same manner. Some dissolve and react strongly, and others partially ionize. It is important to determine the distinction between weak and strong bases not only in the field of chemistry, but also to understand how such substances will act in practical life.

The fundamental difference lies in ionization. A strong base dissolved in water disintegrates entirely, that is, almost all the molecules are decomposed into charged particles. A weak base doesn’t fully ionize, and thus most of the molecules remain in the solution. Although this difference may appear minor on paper, it gives rise to a far larger difference in the actual behaviour of the bases.

Key differences between the two:

• Ionization Rate

Strong bases are completely ionized; weak bases are partially ionized.

• Conductivity

Strong bases are good conductors of electricity (strong electrolytes); weak bases are poor conductors of electricity (weak electrolytes).

• pH Range

Strong bases have a pH that normally ranges between 13-14; weak bases have a pH between 8-12.

• Reaction Speed

Bases with high pH react fast and strongly, whereas slow and weak bases react more slowly and mildly.

• Reversibility

Strong base ionization is irreversible, but weak base ionization is reversible.

Weak Acid and Weak Base – Key Differences

The terms “weak acid” and “weak base” might suggest similar behavior, but they possess different features that distinguish them. Lots of students mix up weak acid and weak base properties, so let us define how weak acid and weak base are different.

Defining the Concepts:

A weak acid is a substance which does not fully ionize in the presence of water. Rather, a minor fraction of its molecules liberate hydrogen ions (H+). There are many weak acid examples, a typical one is vinegar, which is mostly acetic acid (CH 3 COOH ). Only a portion of the acetic acid molecules dissociate to produce H+ and acetate ions in water, and most of them do not dissociate.

Weak bases also ionize partially in water. Instead of completely disintegrating, it takes in hydrogen ions of water molecules. The most typical example of a weak base is ammonia (NH3). On mixing with water, a few ammonia molecules react with water to produce ammonium (NH4+) ions and hydroxide (OH-) ions though most of the ammonia does not react.

Weak Acid and Weak Base Comparison Table:

Property	Weak Acid	Weak Base
Definition	Substance that partially ionizes, releasing H⁺ ions incompletely	Substance that partially ionizes, accepting H⁺ or releasing OH⁻ incompletely
Ion Produced	H⁺ (or H₃O⁺) ions	OH⁻ ions
pH Range	3-6	8-11
Taste	Sour	Bitter
Litmus Paper Reaction	Turns blue litmus red	Turns red litmus blue
Examples	Common weak bases: Acetic acid (CH₃COOH), citric acid, formic acid	Common weak acids: Ammonia (NH₃), methylamine, and aniline
Ionization Equation	HA ⇌ H⁺ + A⁻	B + H₂O ⇌ BH⁺ + OH⁻
Conductivity	Poor conductor of electricity	Poor conductor of electricity
Dissociation Constant	Ka (small value)	Kb (small value)
Buffer Solution	Weak acid + its salt forms a buffer	Weak base + its salt forms a buffer
Neutralization Product	Weak acid + strong base → salt + water	Weak base + strong acid → salt + water
Reversibility	Ionization is reversible (equilibrium)	Ionization is reversible (equilibrium)

Conclusion

To conclude, it is said that a weak base does not fully ionise or accept hydrogen ions (H+ions) in an aqueous solution. Bases have a pH greater than 7. pOH is calculated for the base solutions instead of pH. The dissociation constant for weak bases is always lower than for strong bases, and it determines the strength of a base. Weak bases can create buffer solutions, just like weak acids.

Frequently Asked Questions