A laboratory mixture of sand (non volatile solid) and naphthalene (volatile solid that sublimes) can be conveniently separated into its components by which method?

Introduction / Context:
This question is about separation techniques in basic chemistry. It considers a mixture of sand and naphthalene and asks which laboratory method is best suited for separating them. Knowing the physical properties of the components, such as volatility and sublimation behaviour, is key to choosing the correct method.

Given Data / Assumptions:

• The mixture contains sand, which is a non volatile solid, and naphthalene, which is a volatile organic solid.
• Naphthalene is known to sublime, changing directly from solid to vapour upon heating.
• We want to separate the two substances without decomposing them.
• Options include fractional distillation, sublimation, chromatography, separating funnel and simple filtration.

Concept / Approach:
Sublimation is a process in which certain solids directly convert to vapour on heating and can later re deposit as solid when cooled, without passing through a liquid state. Naphthalene is a classical example of a substance that sublimes easily, whereas sand (mainly silicon dioxide) does not sublime under ordinary laboratory conditions. If we gently heat the mixture, naphthalene vapours can be driven off, collected and re solidified on a cool surface, leaving sand behind. Therefore, sublimation is the ideal method to separate this mixture.

Step-by-Step Solution:
1) Identify the key property of naphthalene: it sublimes on gentle heating, turning into vapour and then re forming solid on cooling.2) Recognise that sand is a non volatile, high melting solid that remains in the solid state when the mixture is gently heated.3) Set up a sublimation apparatus, where the mixture is placed in a dish and covered by an inverted funnel or cold surface.4) Upon gentle heating, naphthalene sublimes, and the vapour condenses as crystals on the cooler surface.5) After sufficient time, the apparatus is allowed to cool, and solid naphthalene is collected from the cold surface, leaving sand in the original container.6) This selective sublimation and re deposition separates naphthalene from sand effectively.

Verification / Alternative check:
Textbooks commonly use mixtures such as ammonium chloride and sand, or naphthalene and salt, to illustrate sublimation as a separation technique. In each case, one component sublimes while the other does not, making sublimation highly effective. Fractional distillation is used for miscible liquids, a separating funnel is used for immiscible liquids and chromatography is mainly used for separating soluble components in a liquid phase. None of those alternatives is as straightforward as sublimation for a simple solid solid mixture where one solid sublimes and the other does not.

Why Other Options Are Wrong:
Fractional distillation of the mixture: This method is meant for separating liquids with different boiling points, not a solid solid mixture with one subliming solid and sand.
Paper chromatography: Useful for separating dissolved components in a liquid mixture, not for dry sand and naphthalene.
Using a separating funnel: Separating funnels are used for immiscible liquids such as oil and water, not for solid solid mixtures.
Simple filtration only: Filtration cannot distinguish between two solid substances when both are insoluble in the chosen solvent; it will not separate sand and naphthalene directly without exploiting sublimation.

Common Pitfalls:
Students sometimes pick filtration because sand is insoluble, forgetting that naphthalene is also a solid and may not be dissolved either. Another mistake is choosing fractional distillation simply because heating and vapour are mentioned, but that process is specific to liquids. A good rule is: when a mixture contains a sublimable solid and a non sublimable solid, sublimation is the preferred separation method. Remembering that naphthalene moth balls slowly disappear by sublimation can help you associate naphthalene with this technique.

Final Answer:
A mixture of sand and naphthalene is best separated by sublimation of naphthalene, leaving sand behind.