Properties of Bases

Bases are substances that can neutralise acids. They are found in laboratories and in many everyday products, including cleaners, antacids, soaps, toothpaste, and materials used in agriculture.

Some bases are weak and relatively safe, while others are strongly alkaline and corrosive. Understanding their properties helps us identify them, use them correctly, and handle them safely.

Physical Properties of Bases

Bases and alkaline solutions have several characteristic properties.

Slippery or Soapy Feel

Many alkaline solutions have a slippery or soapy feel. This is one reason bases are commonly used in soaps and cleaning products.

However, laboratory chemicals should never be touched deliberately to identify them. Strong alkalis can cause serious chemical burns.

pH Above 7

When a soluble base, or alkali, dissolves in water, it produces hydroxide ions (OH⁻).

Alkaline solutions have a pH greater than 7.

• pH 7 = neutral
• pH 8–10 = mildly alkaline
• pH 11–14 = increasingly alkaline

For example, sodium hydroxide dissolves in water:

NaOH → Na⁺ + OH⁻

The hydroxide ions are responsible for many of the properties of alkaline solutions.

Bases Can Conduct Electricity

Solutions of alkalis conduct electricity because they contain mobile ions.

For example, a sodium hydroxide solution contains Na⁺ and OH⁻ ions that are able to move through the solution and carry electrical charge.

Bases and Indicators

We can identify alkaline solutions using indicators.

An indicator changes colour depending on the pH of a solution.

A particularly useful rule to remember is:

Alkalis turn red litmus paper blue.

Universal indicator can also help estimate the pH. Strongly alkaline solutions usually produce a dark blue or purple colour.

Chemical Properties of Bases

Bases undergo several characteristic chemical reactions.

Bases Neutralise Acids

One of the most important properties of a base is its ability to neutralise an acid.

In many neutralisation reactions:

acid + base → salt + water

For example:

2HCl + MgO → MgCl₂ + H₂O

Hydrochloric acid reacts with magnesium oxide to produce magnesium chloride and water.

Alkalis Neutralise Acids

Alkalis also react with acids.

For example:

HCl + NaOH → NaCl + H₂O

At the particle level, the most important reaction is between hydrogen ions and hydroxide ions:

H⁺ + OH⁻ → H₂O

The H⁺ ions from the acid combine with OH⁻ ions from the alkali to form water.

Bases Can React with Ammonium Salts

Some alkalis react with ammonium salts to release ammonia gas.

For example:

NH₄Cl + NaOH → NaCl + H₂O + NH₃

This reaction can be used as a chemical test for ammonium ions.

Common Uses of Bases

Bases have many practical applications.

Cleaning Products

Strong alkalis such as sodium hydroxide are used in some:

• drain cleaners
• oven cleaners
• industrial cleaning products

They are effective because they can react with and break down fats and grease.

Antacids

The stomach naturally contains hydrochloric acid. Sometimes excess stomach acid can cause discomfort.

Antacid medicines may contain bases such as:

• magnesium hydroxide
• calcium carbonate

These bases help neutralise excess stomach acid.

Agriculture

Some soils become too acidic for certain crops.

Materials containing bases, such as calcium carbonate, can be added to acidic soil to raise its pH. This process is often called liming.

Making Soap

Strong alkalis such as sodium hydroxide and potassium hydroxide are used to manufacture soaps.

Toothpaste

Many toothpastes contain mildly basic substances that help neutralise acids in the mouth produced by bacteria.

Strong and Weak Bases

Just as acids can have different strengths, bases can also be described as strong or weak.

Strong Bases

A strong base produces a high concentration of OH⁻ ions because it dissociates essentially completely in water.

Examples include:

• sodium hydroxide (NaOH)
• potassium hydroxide (KOH)

For example:

NaOH → Na⁺ + OH⁻

Strong alkalis can have very high pH values and may be highly corrosive.

Weak Bases

A weak base reacts with water only partially, producing fewer OH⁻ ions under comparable conditions.

A common example is ammonia (NH₃):

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻

The reversible arrow shows that the reaction does not proceed completely to the products.

Comparing the Strength of Bases

Suppose we compare sodium hydroxide and ammonia solutions at the same concentration.

Sodium hydroxide dissociates essentially completely, producing many OH⁻ ions.

Ammonia reacts with water only partially, producing fewer OH⁻ ions.

Therefore, under comparable conditions, sodium hydroxide produces a higher concentration of hydroxide ions and a higher pH.

 

Strength vs. Concentration

Strength and concentration are not the same thing.

Strength describes how completely a base produces ions in water.

Concentration describes how much of the substance is present in a certain volume of solution.

Therefore, a strong base can be dilute, and a weak base can be concentrated.

Adding water to sodium hydroxide makes the solution more dilute, but sodium hydroxide is still classified as a strong base.

Safety When Handling Bases

Strong alkalis can be extremely hazardous.

Concentrated sodium hydroxide and potassium hydroxide are corrosive and can cause severe damage to skin and eyes.

When handling bases in the laboratory:

• wear safety goggles
• use appropriate protective clothing or gloves when instructed
• avoid contact with skin and eyes
• never taste or deliberately touch chemicals
• use only the quantity required
• clean spills according to laboratory procedures
• wash exposed areas immediately with plenty of water and inform the teacher

Strong bases should be treated with the same care as strong acids.

Did You Know?

Bases are particularly good at interacting with fats and oils. Strong alkalis can chemically change fats into soap-like substances.

This helps explain why alkaline chemicals are useful in powerful cleaning products—and also why strong alkalis can be dangerous to skin and other living tissues.

Key Terms

Base: A substance that neutralises an acid.

Alkali: A base that dissolves in water.

Hydroxide ion (OH⁻): An ion associated with alkaline solutions.

Indicator: A substance that changes colour depending on pH.

Strong base: A base that produces ions very effectively in water.

Weak base: A base that reacts or ionises only partially in water.

Corrosive: Able to chemically damage materials or living tissue.

Neutralisation: A reaction between an acid and a base.

Key Takeaways

• Bases neutralise acids.
• Soluble bases are called alkalis.
• Alkaline solutions have a pH above 7.
• Alkalis turn red litmus paper blue.
• Universal indicator usually becomes blue or purple in alkaline solutions.
• Bases are used in cleaning products, antacids, agriculture, toothpaste, and soap production.
• Sodium hydroxide and potassium hydroxide are strong bases, while ammonia is a weak base.
• Base strength and concentration are different concepts.
• Strong alkalis can be highly corrosive and must be handled carefully.