Matter-Nature and its Behaviour Questions for Examination
Question 1. How many elements are in gaseous state at room temperature?
Answer.
11 elements are in gaseous state at room temperature.
Question 2. Name two elements which are in liquid state at room temperature?
Answer.
Mercury, Bromine.
Question 3. What is the state of elements gallium and cesium below 30°C?
Answer.
They are in solid state.
Question 4. When two substances A and B were made to combine, they formed a third substance C. The following observations were recorded for this :
(i) During formation of C from combination of A and B a large amount of heat was evolved,
(ii) The properties of C were different from those of A and B. predict the nature of C.
Answer.
C is a compound
Both the above observations are observed during formation of a compound.
Question 5. Arsenic shows the properties of both (i.e. metals and non-metals). How is it classified ?
Answer.
It is called a semi-metal.
Question 6. What is a crystal lattice ?
Answer.
It refers to a close packed arrangement of atoms in metals.
Question 7. Is it proper to call a mixture as a single substances.
Answer.
No.
Question 8. Can we regard solutions as homogeneous mixtures ?
Answer.
Yes.
Question 9. What is the number of components in a binary solution ? Name them.
Answer.
Two. Solute and solvent.
Question 10. In a gaseous solution what is the state of the solvent ?
Answer.
Solvent is in gaseous state.
Question 11. The solubility of sodium chloride in water increases with rise in temperature while that of
lithium carbonate decreases. Explain
Answer.
The process of dissolution of sodium chloride in water is an endothermic process (i.e. energy is absorbed in the process). In such a process solubility increases with temperature. The process of dissolution of lithium carbonate Ans. in water is an exothermic process (i.e. heat is evolved in the process). In such a process the solubility of solute decreases with increase in temperature.
Question 12. What is a centrifuge ?
Answer.
A centrifuge is a rotating machine which uses centrifugal force to separate solid particles from solution and immiscible liquids from each other. It is also used to separate the components of a suspension.
Question 13. How much water should be mixed with 15 ml of alcohol to prepare a 15% alcohol solutions ?
Answer.
85 ml of water.
Question 14.
(a) Generally, the solubility of a crystalline substance (solid) increases with rise in temperature. Does it increase uniformly in every case ?
(b) Name a substance whose solubility
(i) increases rapidly with rise in temperature,
(ii) increases gradually with rise in temperature,
(iii) increases slightly with rise in temperature
(iv) decreases with rise in temperature
Answer (a).
No, the solubility do not increases uniformly in every case.
Answer (b).
(i) Potassium nitrate
(ii) Potassium chlorate
(iii) Sodium chloride
(iv) Calcium acetate.
Question 15. Is fresh air free of dust particles and impurities of all other kind, a pure substance?
Answer.
No, only elements and compounds are p substance. Air is a mixture and so not pure substance.
Question 16. Why is a compound considered as pure substance but mixture is not considered as pure substance?
Answer.
A compound is a single substance with a fixed composition and so it fulfills the condition required for a pure substance. The m.p. or b.p. of a compound is fixed. These conditions are not fulfilled by a mixture so it is not considered as a pure substance.