Worksheets and lesson ideas to challenge students aged 11 to 16 to think hard about dissolving (GCSE and Key Stage 3)
When you add salt to water the salt disappears. At least that is what appears to happen. But of course we know that the salt does not disappear, rather it forms interactions with the water particles and breaks up into smaller particles that cannot be seen. The mass of the solute and solvent will equal the mass of the solution.
It still fascinates me that temperatures exceeding 800 ºC are required to melt salt and yet salt will dissolve at room temperature. Both processes involve breaking the same strong ionic bonds; it doesn’t seem logical! The answer lies in the fact that when the solute particles form interactions with the water particles – energy is released, and it is this energy that powers the endothermic bond breaking process; how great is that!
What does solute concentration mean?
KS3 starter activity on chemical solutions and concentration. Students are challenged to think deeply about what the term concentration means. They use the terms solute, solvent and solution to consider which solution has the highest concentration. (PDF)
Temperature and dissolving
KS3 practical investigation looking how temperature affects the rate of dissolving. Students measure how long it takes for sugar cubes to dissolve in water at different temperatures. There are two worksheets depending on the resources and time available.
Comparing dissolving and melting
KS3/GCSE thinking tasks looking at the similarities and differences between dissolving and melting. This discussion activity encourages deep thinking about two very familiar processes. Dissolving and melting seem very different, but both processes involve breaking bonds. However, the energy required to break these bonds have very different origins. (PDF)
Key Stage 3 question comparing snow melting and salt dissolving. Students discuss what happens to rock salt and snow in winter. The discussion will hopefully lead students to understand the difference between melting and dissolving. (PDF)
- Particle pictures and the particle model
- Elements mixtures and compounds
- Separating techniques