Here’s a explanation of the common sources of error in qualitative analysis:
1. Impure Samples
- If the sample contains other substances, it can interfere with the tests.
- Example: A metal ion may give a false color or precipitate because of contaminants.
2. Contaminated Reagents
- Using impure chemicals or water can cause wrong reactions or unexpected colors.
3. Human Error
- Mistakes in measuring, adding reagents, or observing results can lead to errors.
- Example: Misjudging the color of a solution or precipitate.
4. Incomplete Reactions
- Sometimes reactions don’t go to completion, so the expected precipitate or color may not form fully.
5. Overlapping Reactions
- Some metal ions or compounds give similar colors or precipitates, causing confusion.
- Example: Iron and chromium may both form colored solutions that look alike.
6. Loss of Sample
- During washing, filtration, or handling, some sample may be lost, affecting the test outcome.
7. Instrumental Limitations
- If using instruments (like spectrophotometers), errors can occur due to improper calibration or sensitivity issues.
Summary:
Most errors in qualitative analysis are due to impurities, similar reactions, human mistakes, or incomplete reactions. Careful handling, pure reagents, and proper observation help reduce these errors.