Physical and Chemical Changes, solution

Total Questions: 33

21. Water passes from the soil into the roots by a physical process called: [67th B.P.S.C. (Pre) 2022]

Correct Answer: (d) Osmosis
Solution:The plants absorb water from the soil with the help of root hairs through osmosis. Osmosis is the specific type of diffusion that involves the net movement of water molecules across a selectively permeable membrane from a region of higher water potential (lower solute concentration) to a region of lower water potential (higher solute concentration).

The water moves into root hair cells by osmosis, as there is a high concentration of minerals/sugars in the cells, and a little water. This decreases the water potential inside the cell, so water molecules move down gradient into the cells. The water can then be moved by xylem in the transpiration stream through the plant and out of its leaves.

22. After cutting cucumber if salt is added, then water comes out due to: [U.P. P.C.S. (Pre) 2021]

Correct Answer: (c) Osmosis
Solution:Osmosis is the process when water (or solvent) molecules move from a region (solution) of low concentration to a region (solution) of higher concentration through a semi-permeable membrane.

When salt is applied to cucumber or cut onion pieces, it makes their surrounding more concentrated than the concentration of their cell sap. Then it causes the water molecules in the cells of the cucumber and the cut onion pieces to move to the surrounding through their cell membrane (which is semipermeable).

23. Consider the following statements: [I.A.S. (Pre) 2005]

  1. During the process of osmosis, the solvent travels from the concentrated solution to the dilute solution.
  2. In the reverse osmosis, external pressure is applied to the dilute solution.

Which of the statements given above is/are correct?

Correct Answer: (d) Neither 1 nor 2
Solution:In the process of osmosis, the solvent moves through a semi-permeable membrane into a region of higher solute concentration from lower concentration to equalize the solute concentration on two sides. While in reverse osmosis, we apply external pressure upon concentrated solution to reverse the movement of solvent, i.e. from more concentrated to weaker dilute solution. The technique is used to purify the solution by making it free from impurities.

24. Consider the following statements with reference to osmosis: [U.P. R.O./A.R.O. (Pre) 2013]

  1. If the semipermeable membrane is placed between the solvent and solution, the solvent molecules will flow through the membrane from pure solvent to the solution.
  2. The process of flow of solvent is called as reverse osmosis.
Correct Answer: (c) Only 1
Solution:If the semipermeable membrane is placed between the solvent and solution, the solvent molecules will flow through the membrane from pure solvent (lower concentration) to the solution (higher concentration). This process of flow of solvent is called osmosis, not reverse osmosis. Hence, only statement (1) is correct.

25. Which one of the following processes is NOT useful for purification of solid impurities? [U.P. R.O./A.R.O. (Pre) (Re. Exam) 2016]

Correct Answer: (a) Distillation
Solution:Distillation is the action of purifying a liquid by a process of heating and cooling. Distillation is generally used for purification of liquid impurities while sublimation and crystallization are used for purification of solid impurities.

26. The technique of chromatography is used to: [42nd B.P.S.C. (Pre) 1997]

Correct Answer: (d) Separate the substances from a mixture
Solution:Chromatography is a separation technique used to separate the different components in a liquid mixture. The separation is based on differential partitioning between the mobile and stationary phases.

Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for more advanced use and thus it is a form of purification.

27. Process of solid camphor turning into camphor vapour is called: [44th B.P.S.C. (Pre) 2000]

Correct Answer: (d) Sublimation
Solution:Solid camphor directly changes into camphor vapour and this process is called sublimation. The sublimation is the process in which some substances upon heating directly change into vapour form and when cooled again directly turns into solid form.

28. A sample of any of the following substances disappears after sometime when exposed to air like camphor, naphthalene or dry ice. This phenomenon is called: [U.P.P.C.S. (Pre) 2019]

Correct Answer: (a) Sublimation
Solution:Sublimation is the transition of a substance directly from the solid to the gas phase, without passing through the intermediate liquid phase. Substances like camphor, naphthalene or dry ice (solid carbon dioxide) display this phenomenon.

29. The conversion of a solid directly into gas is called as: [63rd B.P.S.C. (Pre) 2017]

Correct Answer: (a) Sublimation
Solution:Sublimation is the process where a solid turns directly into gas without passing through the liquid phase.

30. Mixture of sand and naphthalene can be separated by: [66th B.P.S.C. (Pre) 2020]

Correct Answer: (a) Sublimation
Solution:Naphthalene displays the phenomenon of sublimation, which is the transition of a substance directly from the solid to gas phase upon heating. Hence, a mixture of sand and naphthalene can be separated by sublimation.