In chemistry, qualitative analysis is the process of identifying the chemical composition of a substance or mixture without necessarily measuring how much of each component is present. In other words, it answers the question: “What is in this sample?” rather than “How much of it is there?” (which is quantitative analysis).
Key Points:
- Purpose:
- To detect the presence of certain ions, elements, or functional groups in a sample.
- Commonly used to identify cations, anions, and organic functional groups.
- Methods:
Qualitative analysis usually involves observing chemical reactions that produce noticeable changes such as:- Color change
- Precipitate formation
- Gas evolution
- Flame tests
- Examples:
- Adding silver nitrate to a solution to check for chloride ions (Cl⁻); a white precipitate of AgCl forms if Cl⁻ is present.
- Using flame tests to detect metal ions like sodium (yellow flame) or potassium (lilac flame).
- Reacting acids with carbonates to see effervescence (CO₂ gas), indicating carbonate presence.
- Applications:
- Analyzing unknown salt mixtures.
- Detecting pollutants in water.
- Forensic analysis to identify substances.
In short, qualitative analysis tells you what is present, not how much.