Exploring Mixtures and their Separation · Lesson 9 of 13
Sublimation
“Camphor takes the vapour shortcut while sand stays exactly where it was.”
• Explain sublimation and deposition. • Describe how camphor is separated from sand. • Distinguish sublimation from evaporation. • Identify other sublimable substances. • Explain why alloy components are not separated by these physical methods.
Heat a mixture of camphor and sand gently. The camphor seems to disappear, yet a white solid later appears on a cool surface above it. The camphor has not melted into a liquid. It has travelled through the vapour state and returned directly to a solid.
Sublimation is the direct change of a solid into vapour below its melting point without passing through the liquid state.
Deposition is the direct change of vapour into solid without passing through the liquid state.
Activity: Let Us Explore
Place a small mixture of crushed camphor and sand in a clean, dry china dish. Cover it with an inverted dry glass funnel whose narrow end is plugged loosely with cotton. Set the dish on wire gauze and heat it gently.
Camphor vapour rises and touches the cooler inner wall of the funnel, where it deposits as white solid camphor. Sand remains in the china dish because it does not sublime under these conditions. After cooling, the two solids can be collected separately.
Problem
Explain the complete separation in terms of physical changes.
- 1.Gentle heating supplies energy to camphor.
- 2.Camphor changes directly from solid to vapour by sublimation.
- 3.Sand remains solid in the china dish.
- 4.Camphor vapour reaches the cooler funnel wall.
- 5.It changes directly back to solid by deposition.
- 6.The deposited camphor and remaining sand are now in different places.
Pause and Ponder
| Process | Starting State | Final State | Liquid Stage |
|---|---|---|---|
| Sublimation | Solid | Vapour | Absent |
| Deposition | Vapour | Solid | Absent |
| Evaporation | Liquid | Vapour | Process begins with a liquid |
Naphthalene can also be separated from a non-subliming solid such as sand. Solid carbon dioxide, called dry ice, sublimes and is useful for keeping materials cold because it changes directly into gas rather than leaving a liquid puddle.
Problem
A mixture contains naphthalene and sand. Why is sublimation appropriate?
- 1.Naphthalene sublimes on heating.
- 2.Sand does not sublime under the same conditions.
- 3.Heating turns only naphthalene into vapour.
- 4.Cooling deposits naphthalene on a separate surface.
- 5.The different response to heating is the property used for separation.
Metals can mix when melted and then solidify as a uniform material called an alloy. Brass contains mainly copper and zinc, bronze contains mainly copper and tin, and stainless steel contains iron with elements such as carbon, chromium, nickel and molybdenum.
An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal, formed to obtain useful properties.
The components of an alloy are mixed uniformly at the particle level and cannot be separated by the simple physical methods discussed in this chapter. Alloys are deliberately produced to gain strength, rigidity or resistance to corrosion.
Use only a small sample, heat gently under adult supervision and allow the apparatus to cool before touching or collecting deposits.
Quiz
Which description best matches Sublimation?
Which description best matches Deposition?
Which term matches this description: Sublimation is the direct change of a solid into vapour below its melting point without passing through the liquid state.
Which term matches this description: Deposition is the direct change of vapour into solid without passing through the liquid state.
Which statement is a key takeaway from this lesson?
Practice Problems
- Differentiate sublimation and deposition.
- Why does sand remain in the dish during the camphor activity?
- How is evaporation different from sublimation?
- Explain why a magnet or filter cannot separate the components of brass.
Key Takeaways
• Sublimation changes a solid directly into vapour. • Deposition changes vapour directly into solid. • A sublimable solid can be separated from a non-subliming solid. • Naphthalene, camphor and dry ice show sublimation. • Alloy components cannot be separated by the simple physical methods considered here.