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NCERT Solutions for Class 9th Science Chapter 5 .4.2 Sublimation — In-text Questions

Book page 845 Updated on2026-09-08

Q1.
Can you think of any other mixtures where sublimation can be used to separate the components?
Answer

Yes — any mixture in which exactly one component sublimes on gentle heating.

MixtureComponent that sublimesComponent left behind
Naphthalene and sandNaphthaleneSand
Ammonium chloride and common saltAmmonium chlorideCommon salt
Camphor and common saltCamphorCommon salt
Iodine and sandIodineSand
Dry ice mixed with an ordinary solidSolid carbon dioxideThe other solid
The condition for the method to work: sublimation separates a solid–solid mixture only when one component vaporises directly below its melting point while the other stays unchanged at that temperature. If both sublime, or if neither does, the method is useless and you must use some other difference — solubility, magnetism or density.
Q2.
Is it possible to dissolve one metal in another?
Answer

Not at room temperature — but yes, if the metals are melted first. The homogeneous solid formed when such a molten mixture solidifies is called an alloy.

AlloyApproximate compositionWhy it is made
BrassAbout 80 % copper and 20 % zincHarder than copper, easy to shape, does not corrode readily
BronzeAbout 80 % copper and 20 % tinStrong and hard-wearing; used for statues and bells
Stainless steelIron with carbon 0.03 – 0.8 %, chromium 16 – 18 %, nickel 10.0 – 14.0 %, molybdenum 2.0 – 3.0 %Strong and rust-resistant; used for utensils and instruments
Why melting is needed: In a solid metal the atoms are locked into a fixed lattice and cannot move past one another, so one metal cannot spread into another. Melting frees the atoms to move, and the two kinds of atoms then mix right down to the atomic level. On cooling, the mixture solidifies with the atoms still mixed, so the alloy is a homogeneous mixture and looks like a single metal. Because the mixing is atomic and not just physical, no physical method can separate an alloy back into its metals.
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