Qualitative analysis is the identification of the ions present in a salt through a set of standard chemical tests.
Malay: Analisis kualitatif · Chinese: 定性分析
Qualitative analysis is the identification of the ions present in a salt through a set of standard chemical tests. The word “qualitative” means it tells you which ions are there, not how much of each, so the whole exercise is about matching observations to ions. It works in two halves: tests for the positive ion (the cation) and tests for the negative ion (the anion).
A worked example shows the logic. Add sodium hydroxide solution to an unknown salt: a blue precipitate points to copper(II) ions, a green one to iron(II), and a brown one to iron(III). Some precipitates dissolve in excess alkali, which narrows it further. For the anion, a separate test is used for each: adding dilute acid and testing an evolved gas for carbon dioxide identifies a carbonate, while acidified silver nitrate giving a white precipitate identifies a chloride, and acidified barium chloride giving a white precipitate identifies a sulfate. Each observation is read as evidence for one ion.
The confusion to avoid is between qualitative and quantitative analysis. Qualitative analysis answers “which ions are present”; quantitative analysis, such as a titration, answers “how much is present”. Mixing the two words in an answer costs marks. A second slip is skipping the conditions, many anion tests only work when the solution is first acidified to remove interfering ions, and leaving that out gives a false positive.
Within this chapter qualitative analysis draws the ideas of ions, salts and precipitation together into a diagnostic skill, and it is a favourite of the practical paper. Our teachers drill the standard tests as a decision tree so you move from observation to conclusion without guessing.
Want a teacher to make this click?
We teach SPM Chemistry one to one, so your child understands it and scores it.
from RM50/hr · One-hour paid trial · Same-day reply