A fair comparison of dissolving
In an original fictional classroom investigation, two groups compare how quickly equal portions of a soluble solid dissolve in water. One group uses warm water and stirs continuously, while the other uses cooler water and does not stir. Both report a time, but the class has not agreed on an observable endpoint or checked whether the portions and water volumes match. The teacher wants students to study the effect of temperature using an appropriate supervised activity. The task supplies no permission to handle unknown chemicals or heat equipment independently. Students must improve the comparison and explain what the first observations can establish without inventing missing measurements.
1. Why is the first comparison limited?
Read the worked answer
Temperature and stirring both changed, with other conditions not fully checked, so the difference cannot be assigned to temperature alone.
2. Improve the design.
Read the worked answer
Use suitable matched quantities, the same stirring procedure and endpoint, appropriate temperature control and repeated observations under supervision.