1. Introduction
Acids are substances commonly found around us — in lemons, oranges, vinegar, and curd. They show specific physical properties that help us identify them even before performing any chemical test.
These properties describe how acids look, feel, smell, and behave in simple, observable ways.
2. Main Physical Properties of Acids
Acids have certain characteristics that make them easy to identify. Below are the most important physical properties explained in simple words.
2.1. Sour Taste
Acids naturally taste sour. For example, lemon juice contains citric acid, and vinegar contains acetic acid.
Important: Never taste acids in the laboratory. This information is only for understanding natural acids in food.
2.2. Effect on Litmus Paper
Acids turn blue litmus paper red. This is a quick and common way to test whether a substance is acidic.
2.3. State and Appearance
- Many acids are liquids (like hydrochloric acid, sulphuric acid).
- Some acids are solids (like citric acid and oxalic acid crystals).
- Most mineral acids are colourless, but some organic acids may appear white or pale.
2.4. Solubility in Water
Most acids dissolve in water. When they dissolve, they release hydrogen ions \( H^+ \), which is what gives them their acidic nature.
This is why even strong acids must always be diluted carefully.
2.5. Electrical Conductivity
Acids conduct electricity when dissolved in water. This is because they release charged particles (ions) such as:
\( \text{H}^+ \) and \( \text{Cl}^- \)
These ions allow electric current to pass through the solution.
2.6. Corrosive Nature
Strong mineral acids like sulphuric acid and hydrochloric acid are corrosive. They can damage skin, metals, and other materials.
Because of this, acids must be handled with care in laboratories and industries.
2.7. Smell
Some acids have a sharp, irritating smell. For example, acetic acid (in vinegar) has a strong, sour smell.
However, many strong acids used in labs do not have a noticeable smell, but they can still be dangerous.
3. Summary of Physical Properties
To quickly remember, acids generally have the following physical properties:
- Sour taste
- Turn blue litmus red
- Often colourless liquids
- Soluble in water
- Conduct electricity in aqueous solution
- Corrosive (for strong acids)
- May have a sharp smell
These features help us understand and identify acids easily in both natural and laboratory settings.