Grade 6 → Acids, Bases and Salts ↓
Definition of Bases
In chemistry, it is fundamental to understand the concept of bases along with acids and salts. Let's look at the definition, properties and examples of bases in a detailed and simple way so that learning about this essential chemistry topic becomes a little easier.
What are the bases?
A base is a chemical substance that can accept a hydrogen ion (proton) or, more commonly, donate a pair of valence electrons to form a bond. Bases often taste bitter and seem slippery. They are the opposite of acids, which release hydrogen ions into solution. When acids and bases meet, they neutralize each other, often forming water and a salt. The concept of a base can be illustrated with many examples and types, such as:
Simplest example of a base
The most basic example of a base is sodium hydroxide (NaOH
). When dissolved in water, it releases hydroxide ions (OH -
).
NaOH (s) → Na + (aq) + OH - (aq)
NaOH (s) → Na + (aq) + OH - (aq)
OH -
ions are important in identifying bases. In this simple system, sodium hydroxide dissociates completely in water, which is characteristic of a strong base.
Properties of bases
Bases have a number of characteristic properties:
- Taste: Bases usually have a bitter taste. An example of this is the bitter taste of soap.
- They feel slippery to the touch, like soap. This is due to the saponification process, in which alkalis react with oils to form a soap-like texture.
- Reaction with acids: Bases react with acids and follow the process of neutralization. This results in the formation of water and salt.
- Electrical conductivity: Bases in aqueous solution can conduct electricity. This is due to the presence of mobile ions.
- Colour change with indicators: Bases turn red litmus paper blue. They also change the colour of some indicators, which are used to determine the presence of bases.
Types of bases
Bases can be classified based on their strength and structure.
Strong and weak bases
Strong bases dissociate completely in water. Examples include:
NaOH
(sodium hydroxide)KOH
(potassium hydroxide)Ba(OH) 2
(barium hydroxide)
Weak bases only partially dissociate in water. Examples include:
NH 3
(ammonia)CH 3 NH 2
(methylamine)C 5 H 5 N
(pyridine)
Organic and inorganic bases
Inorganic bases are usually metal oxides, hydroxides and carbonates. Examples are:
Ca(OH) 2
(calcium hydroxide)LiOH
(lithium hydroxide)
Organic bases contain primarily nitrogen atoms. Examples include:
C 5 H 5 N
(pyridine)(C 2 H 5 ) 3 N
(triethylamine)
pH scale and alkali
The pH scale is a numerical scale from 0 to 14 used to specify the acidity or alkalinity of an aqueous solution. The pH value is a measure of hydrogen ion concentration, and is calculated using the formula:
pH = -log[H + ]
pH = -log[H + ]
pH value
- A pH value less than 7 indicates an acidic solution.
- A pH value equal to 7 indicates a neutral solution.
- A pH value greater than 7 indicates an alkaline solution.
Bases have a pH value greater than 7. For example:
- A solution with pH 8 is weakly alkaline.
- A solution with a pH of 14 is a very strong alkaline.
Common examples of bases
This section explores common concepts you may encounter in everyday life or in the lab:
Sodium hydroxide (NaOH
)
- It is also known as caustic soda or lye.
- It is used in making soap and cleaning drains.
Ammonia (NH 3
)
- It is commonly found in household cleaning products.
- Used as a fertilizer in agriculture.
Calcium hydroxide (Ca(OH) 2
)
- This is called slaked lime.
- Used in agriculture to treat acidic soils.
How bases react
Bases participate in a variety of chemical reactions due to their ability to accept a proton or donate an electron pair:
Neutralization reaction
Neutralization is a chemical reaction between an acid and a base, resulting in the formation of water and salt:
HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l)
HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l)
In this response:
HCl
is hydrochloric acid, an acid.NaOH
is sodium hydroxide, a base.- They react to form sodium chloride (
NaCl
), a salt, and water (H 2 O
).
Reaction with metals
Some react with alkali metals to form hydrogen gas. For example, when sodium hydroxide reacts with zinc:
2NaOH (aq) + Zn (s) → Na 2 ZnO 2 (aq) + H 2 (g)
2NaOH (aq) + Zn (s) → Na 2 ZnO 2 (aq) + H 2 (g)
This shows how bases can react under certain conditions, resulting in the release of hydrogen gas.
Industrial and everyday uses of bases
Alkalis play an important role in a variety of industrial and everyday applications:
Soap and detergent manufacturing
The production of soap involves the process of saponification, in which fats react with a strong alkali such as sodium hydroxide (lye).
Household cleaning products
Many household cleaners contain alkalis such as ammonia to remove grease and dirt.
Paper and textile production
Alkalis are used in the pulp making process in the paper industry and for treating fibres in textile manufacturing.
Antacids
Bases such as magnesium hydroxide are used as antacids to neutralise stomach acid and relieve indigestion.
Safety precautions when handling bases
Although alkalis are widely used, they often require careful handling due to their potentially corrosive nature:
- Always wear protective equipment such as gloves and goggles when working on strong bases.
- Work in a well-ventilated area to avoid fumes from volatile alkalis.
- Know the emergency procedures for accidental contact with skin, eyes or swallowing.
Learning and recognizing bases
Bases can be identified using a variety of indicators and experimental methods:
Litmus test
Litmus is an indicator, and one of the simplest tests for alkalis is the litmus paper test. Alkalis will turn red litmus paper blue. This is an easy way to identify common bases such as ammonia or sodium hydroxide in a laboratory setting.
Universal indicator
A universal indicator might provide a full range of colors for different pH levels, where bases would appear in green and blue, indicating a pH greater than 7.
Titration
Titration is a laboratory method used to determine the concentration of an acid or base. Using a standard solution of known concentration, the end point of the reaction can be measured, which helps to calculate the unknown concentration of the solution being tested.
HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l)
HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l)
Role of bases in the environment
Bases also have important roles in the environment:
Soil treatment
Calcium hydroxide is used to treat acidic soils, improving growth conditions for a variety of crops by increasing the soil's pH level.
Water treatment
Bases are used to neutralize acidic water bodies, often counteracting the effects of acid rain, thus preserving aquatic life and water quality.
Conclusion
Understanding bases, their properties, and the way they interact in our environment and daily life is fundamental in chemistry. From supporting industrial processes to maintaining ecological balance, the role of bases is indispensable. Students should aim to understand the basic principles, safety measures, and applications of bases, preparing themselves with the knowledge to explore further into the vast world of chemistry.