CBSE Class 7 Science Advanced Chemistry Classification of Matter Very Short Answer Questions Set 03

Very Short Answer Questions

Question 1. State whether true or false: Iodine is a lustrous metal.
Answer:
False. Iodine is a lustrous nonmetal.
In simple words: Iodine is shiny but it is a nonmetal.

Teacher's Note:
1. Iodine and graphite are the lustrous nonmetals.
2. Lustre alone does not make an element a metal.

Question 2. State whether true or false: Sodium floats on water.
Answer:
True
In simple words: Sodium is less dense than water, so it floats.

Teacher's Note:
1. Lithium, sodium and potassium are lighter than water.
2. Most metals are denser than water.

Question 3. State whether true or false: Ammonium chloride is a sublimable substance.
Answer:
True
In simple words: On heating, ammonium chloride changes directly into vapour.

Teacher's Note:
1. This is why it is separated from salt by sublimation.
2. Camphor and iodine behave similarly.

Question 4. State whether true or false: The components of compound are separated by physical processes.
Answer:
False. They are separated by chemical methods.
In simple words: Compounds can only be broken by chemical methods.

Teacher's Note:
1. Physical methods separate mixtures.
2. A compound's parts are chemically combined.

Question 5. State whether true or false: Sublimation is the process of the conversion of a solid to its liquid state.
Answer:
False. Sublimation is the conversion of a solid directly to its vapour (gaseous) state. Solid to liquid is melting.
In simple words: Sublimation is solid to gas without melting.

Teacher's Note:
1. Solid to liquid is melting.
2. Check where the liquid stage is missing.

Question 6. ______ is a surface phenomenon, whereas boiling is a ______.
Answer:
Evaporation, bulk phenomenon
In simple words: Evaporation takes place from the surface only; boiling takes place throughout the liquid.

Teacher's Note:
1. Surface versus bulk is the main difference.
2. See Table 1.3 in the notes.

Question 7. ______ state of matter is incompressible.
Answer:
Solid
In simple words: In a solid the molecules are already tightly packed, so it cannot be squeezed.

Teacher's Note:
1. Gases are highly compressible, liquids slightly.
2. No gaps means no compression.

Question 8. A pure substance is ______ in nature.
Answer:
homogeneous
In simple words: A pure substance is uniform throughout.

Teacher's Note:
1. One kind of particle gives uniform composition.
2. Elements and compounds are both homogeneous.

Question 9. ______ is a lustrous nonmetal.
Answer:
Iodine
In simple words: Iodine is a shiny nonmetal.

Teacher's Note:
1. Graphite is another lustrous nonmetal.
2. Most nonmetals are dull.

Question 10. Generally, the components of a compound are separated by ______.
Answer:
chemical methods
In simple words: A compound can be split only by a chemical reaction.

Teacher's Note:
1. Chemical combination needs chemical separation.
2. Mixtures use physical methods.

Question 11. ______ is the nonmetal which is a good conductor of electricity.
Answer:
Graphite (a form of carbon)
In simple words: Graphite is a nonmetal that conducts electricity.

Teacher's Note:
1. It is used in pencils and electrodes.
2. It is an exception to the general rule about nonmetals.

Question 12. ______ in humidity increases rate of evaporation.
Answer:
Decrease
In simple words: Drier air lets a liquid evaporate faster.

Teacher's Note:
1. Humidity and evaporation rate are inversely related.
2. Wet clothes dry faster on a dry day.

Question 13. A mixture of two solids is generally ______ while a mixture of any number of gases is ______.
Answer:
heterogeneous, homogeneous
In simple words: Solid mixtures are usually uneven, while gases always mix evenly.

Teacher's Note:
1. Gases diffuse completely, so they are uniform.
2. Sand and salt look uneven; air does not.

Question 14. Mixture of iron filings and sand can be separated by ______
Answer:
magnetic separation
In simple words: A magnet pulls out the iron filings and leaves the sand.

Teacher's Note:
1. Use a method that suits one component's property.
2. Iron is magnetic and sand is not.

Question 15. ______ and ______ are the suitable separation methods for mixtures of soluble solids in liquids.
Answer:
Evaporation and distillation
In simple words: To get back a dissolved solid, the liquid is evaporated or distilled off.

Teacher's Note:
1. Distillation also recovers the liquid.
2. Filtration does not work for dissolved solids.

Teacher's Note:
1. Decide first whether each item is a pure substance or a mixture.
2. 'Impure compound' fits none of the entries.

Teacher's Note:
1. Write the starting and ending state of each process.
2. Entry e is the odd one, since it skips the liquid state.

Teacher's Note:
1. Sodium chloride and ammonium chloride are both solids, so a solid method is needed.
2. Distillation is used where the solid is dissolved.