Reaction between an acid and a base to show the process of neutralization

  Our Objective

To show that the reaction between HCl and NaOH is a neutralisation reaction.

  The Theory

What is a Neutralization Reaction?

A neutralization reaction is a chemical reaction that occurs when an acid and a base react quantitatively to produce salt and water as products.

The Chemistry behind neutralization Reaction

When an acid and a base react to produce water and salt by combining H+ and OH- ions, a neutralisation reaction occurs. The pH of a strong acid and a strong base, when neutralized, is 7. When a strong acid and weak base are neutralised, the resultant pH is less than 7, and when a strong base neutralises a weak acid, the resulting pH is more than 7.

When you touch the tube right after it has been neutralized, it feels hot. In a neutralization, reaction heat is always produced. When an acid reacts with a base, a new substance is produced. This new substance is called salt. Salt may be acidic, basic, or neutral.

Consider the reaction between HCl and NaOH in aqueous medium


The liquid phenolphthalein is colourless. When added to a basic solution, its colour changes to pink. There is no colour change with acids.

Depending on the amounts of acidic and basic solutions combined, the final solution can be acidic, basic, or neutral. When an acid solution and a base solution are combined in the proper proportions, both the base's basic and acidic properties are neutralised or eliminated. The finished product is neither acidic nor basic. It is neutral. To understand the changes, we us Indicators and it is defined as when it is in contact with acids and bases, an indicator is a type of "dye" that changes colour. If the colour of the substance changes, this indicates whether the substance is an acid or a base.

The three most popular indicators for testing acids and bases are phenolphthalein, methyl orange, and litmus.

Indicator Colour in acid(pH < 7) Colour at pH = 7 Colour in base(pH > 7)
Red cabbage water Red, pink Purple Blue,green,yellow
Turmeric water Yellow Yellow Red
Phenolphthalein Colourless Colourless Pink,red
Universal indicator Red, orange, yellow Green Blue, violet, purple

Application of Neutralization Reaction

  • In our digestive systems, food must be neutralised as it travels from our stomach to our intestines. However, an alkaline environment is required for nutrients to be absorbed through the intestine walls. To achieve this favourable condition, antacid bicarbonate is produced.
  • The majority of waste that comes in the form of industrial effluents contains a significant amount of toxicity that is harmful to our environment. As a result, before they can be discarded, we must first neutralise their toxicity. Different chemicals are used depending on the application. Sodium Bicarbonate, Magnesium Hydroxide, Calcium Oxide, and Calcium Carbonate are just a few examples.
  • There are certain conditions that must be met for optimal plant growth in any soil. The following are some examples of materials that can be mixed into the soil to neutralise acidity:
  • Calcium Carbonate is a mineral made up of calcium and carbon (Limestone)
  • Calcium Hydroxide (CaCO3) (Slaked lime)

What purpose does neutralisation serve?

Farmers use lime to neutralise acidic soils (calcium oxide). Hydrochloric acid is found in the gut, and too much of it causes indigestion. Antacid tablets contain bases such as magnesium hydroxide and carbonate to neutralise excess acid.  To neutralise excess acid antacid tablets, contain bases such as magnesium hydroxide and magnesium carbonate.

In everyday life, what is the neutralisation reaction?

Vinegar is used to treat wasp stings that are alkaline in nature. Baking powder is used to treat bee stings and ant bites that are acidic in nature. Toothpaste contains bases that neutralise the acid produced by bacteria in our mouth. Baking powder is commonly used to make cakes grow.

Learning Outcomes

Students will be able to

  1. Identify the species involved in a neutralisation reaction and their names: acid, base, and salt
  2. From a word or a symbolic chemical equation, identify the acid, base, and salt
  3. Formulate chemical equations for neutralisation reactions
  4. Understand that an acid-alkali reaction can be reduced to the reaction of H+ ions with OH– ions to produce water
  5. Explain the typical characteristics of a neutralisation reaction, such as the formation of a salt and water
  6. Explain how the pH of a solution changes during an experiment
  7. Explain the physical changes that occur during a neutralisation reaction, such as heat release