Cobalt Chloride Paper Practical for O-Level Biology
A focused O-Level Biology 6093 Paper 3 guide to cobalt chloride paper, water vapour evidence, transpiration comparisons, controls, safety, and ACE wording.
The core idea is simple: Cobalt chloride paper is evidence for water, often used in transpiration questions.
Use it as a working check: Compare equal areas, equal exposure times, and the same starting paper colour before drawing a conclusion.
Then go one layer deeper: In Paper 3, the best answers say what changed, what it shows about water vapour, and why the comparison was fair.
The SEAB O-Level Biology 6093 syllabus lists cobalt chloride paper among possible Paper 3 practical materials. This focused guide links that material to water vapour and transpiration reasoning.
For wider plant-water practicals, use the O-Level Biology potometer and transpiration guide. For the full subject route, use the O-Level Biology practical hub.
What Cobalt Chloride Paper Shows
Dry cobalt chloride paper is used as an indicator for water. In school practical reasoning, a colour change shows that water is present.
In leaf questions, the practical is usually not asking "does water exist?" It is asking where water vapour is released faster, or how a condition affects transpiration.
A Fair Comparison
To compare two leaf surfaces or two conditions, keep the comparison fair.
| Control | Why it matters |
| Same starting colour of paper | A partly damp paper gives a false head start. |