Bihar Board - Class 12 Chemistry - Chapter 2: Solutions Short Answer Question
The short question answers for Chapter 2: solutions of Class 12 Chemistry are provided here in English. These questions are prepared based on the NCERT curriculum for Class 12. They will help students understand the chapter easily. These short question answers will be useful not only for the Class 12 board exams but also for entrance exams like NEET. The questions and answers for Bihar Board Class 12 Biology, Chapter 2: solutions, have been prepared by expert teachers at Vidyakul.
Short Questions and Answers
Q. 1. State the two characteristics of the supersaturated solution.
Ans. There are two characteristics of the super saturated solution is : (i) If a crystal of solute is added to a supersaturated solution, crystallization occurs rapidly. (ii) Super saturated solutions contain more solute than they should have at a particular temperature.
Q. 2. Which type of deviation is shown by the solution formed by mixing cyclohexane and ethanol?
Ans. Hydrogen bonds exist among the molecules of ethanol (i.e., strong forces). When cyclohexane is added to ethanol, the cyclohexane molecule will come in between the ethanol molecules and disturb the hydrogen bondings. The forces between ethanol and cyclohexane will be weaker than the previous forces (H-bonding), hence there will be positive deviation.
Q. 3. What are ideal and non-ideal solutions? Mention one nearly ideal solution.
Ans. The solutions which obey Raoult’s law and for which Hmix and Vmix are zero, are termed as ideal solutions. The solutions which do not obey Raoult’s law are called non-ideal solutions. Typical ideal solutions : Hexane + Heptane Ethyl bromide + Ethyl iodide Benzene + Toluene
Q. 4. Methanol is soluble in water but insoluble in octane. Explain briefly.
Ans. Methanol and water both are polar and hydrogen bond forming molecules. Thus, they will form a homogeneous solution. Whereas octane is a non-polar molecule and will not form a solution with methanol.
Q. 5. What is the Van’t Hoff factor? How does it modify the equation for the elevation of boiling points?
Ans. The Van’t Hoff factor is expressed as Or Modified equation for the elevation of boiling point
Q. 6. Define the term solution. How many types of solutions are formed? Write briefly about each type with an example.
Ans. Solution: It is a homogeneous mixture of two or more components whose composition may be varied within limits. There are nine types of solutions.
Types of Solutions:
| Solvent | Solute | Example |
|---|---|---|
| Gas | Gas | Mixture of gases, air |
| Gas | Liquid | Water vapors in air, mist |
| Gas | Solid | Sublimation of a solid into a gas: vapors in air |
| Liquid | Gas | Gas dissolved in water (aerated drinks like Limca) |
| Liquid | Liquid | Mixture of miscible liquids, e.g., alcohol in water, acetone in water |
| Liquid | Solid | Sugar solution, salt solution in water |
| Solid | Gas | Adsorption of gases over metals; hydrogen over palladium |
| Solid | Liquid | Mercury in zinc, mercury in gold |
| Solid | Solid | Alloys, Brass etc. |
Q. 7. State Raoult’s law. If is the elevation of boiling point of a solvent and m is the number of moles of solute per kg of solvent, what is the relationship between and ?
Ans. Raoult’s law : It states that whenever a nonvolatile solute is added to a volatile solvent the vapour pressure of the solvent is lowered and the lowering of vapour pressures directly proportional to the mole fraction of the solute added.
where, is the vapour pressure of the pure solvent. is the vapour pressure of the solution. is the mole fraction of non-volatile solute. Thus, according to Raoult’s law, the relative lowering of vapour pressure is equal to the mole fraction of the solute in solution.
Q. 8. Define molar conductivity of an electrolytic solution. Mention the effect of the temperature on molar conductivity.
Ans. Molar conductivity is defined as electrolytic conductivity power of all the ions furnished by mol of the electrolyte at a given concentration in solution. It is given as where Molar conductivity Specific conductivity. Concentration in molar per liter.
Effect of temperature on molar conductivity. The speed of movement of ions increases with an increase in temperature. Therefore, molar conductivity increases with temperature.
Q. 9. What is antifreeze?
Ans. A substance like ethylene glycol which is added to water to lower its freezing point.
Q. 10. Why solution freezes at lower temperature than water but boils at higher temperature than water?
Ans. When a solute is dissolved in water, the vapour pressure decreases. Hence solution boils at a higher temperature, while solvent freezes at a lower temperature.
Q. 11. Two liquids and boil at and respectively. Which one of them has higher vapour pressure at?
Ans. Lower the , more volatile the liquid. Hence will have higher vapour pressure at .
Q. 12. Explain why non-ideal solutions deviate from Raoult’s law?
Ans. Non-ideal solutions deviate from Raoult’s law because the new forces of interaction between the components (interactions) are different from those present in the pure components (or interactions).
Q. 13. Under what conditions van’t Hoff factor is (i) equal to one, (ii) greater than , (iii) less than.
Ans. (i) , when the solute does not undergo any association or dissociation in the solution. (ii) , when the solute undergoes dissociation in the solution. (iii) , when the solute undergoes association in the solution.
Q. 14. Why does an azeotropic mixture distill without any change in composition?
Ans. Such a mixture on boiling forms vapors in the same mole fraction of the two components as present in the liquid mixture.
Q. 15. Henry’s law constant for and at are , and respectively. What will be the order of their solubility in water at the same pressure and why?
Ans. As are in , the Henry’s law will be in the form . Thus, greater the value of greater is the solubility. Thus solubility will be in the order .
Q. 16. Why is the dissolution of some solid compounds in exothermic while that of some others in endothermic?
Ans. If solute-solvent interactions are stronger than solute-solute or solvent-solvent interactions, energy is released and the dissolution is exothermic. If solute-solvent interactions are weaker than solute-solute or solvent solvent interactions, energy is absorbed and the dissolution is endothermic.
Q. 17. When and why is molality preferred over molarity in handling solutions in chemistry?
Ans. Molality is preferred when studies are made independent of temperature. This is because molality involves masses which do not change with temperature.
Q. 18. of a liquid A where mixed with of liquid B. The volume of the resulting solution was found to be. What do you conclude?
Ans. Decrease in volume means stronger intermolecular forces of attraction on mixing. This implies that the solution shows negative deviation from Raoult’s law.
Q. 19. Two liquids and mixing produces a warm solution. Which type of deviation from Raoult’s law does it show?
Ans. Warming up of the solution on mixing in solution indicates that the process is exothermic ( is -ve). This implies that the solution shows negative deviation from Raoult’s law.
Q. 20. Which colligative property is preferred for the molar mass determination of macromolecules and why?
Ans. Osmotic pressure determination is better suited for molar mass determination of macromolecules like proteins, polymers etc. Changes observed in other colligative properties for such solutions are usually very low and can’t be measured easily.
Q. 21. Sodium chloride or Calcium chloride is used to clear snow form the roads. Why?
Ans. These salts depress the freezing point of water to such an extent that it cannot freeze to form ice. Hence, it melts off easily at the prevailing temperature.
Q. 22. What are colligative properties? Mention them.
Ans. Colligative properties are those which depend upon the number of particles (atoms, molecules or atoms) of the solute and not on their nature. There are 4 colligative properties.
(i) Relative lowering of vapour pressure. (ii) Elevation in Boiling point. (iii) Depression in Freezing point. (iv) Osmosis or osmotic pressure.
Q. 23. What happens when blood cells are placed in pure water?
Ans. Due to osmosis, water molecules move into blood cells through the cell walls. As a result blood cells swell and may even burst.
Q. 24. What do you expect to happen when Red Blood Corpuscles (RBC’s) are placed in (i) solution, (ii) solution?
Ans. (i) They will shrink due to plasmolysis. (ii) They will swell and may even burst. This is because RBC’s are isotonic with Solution.
Q. 25. Based on solute solvent interactions, arrange the following in order of increasing solubility in n-octane and explain. Cyclohexane, .
Ans⇒ octane is a non-polar liquid and solubility is governed by the principle that dissolve like. Keeping this in view, the increasing order of solubility of different solutes is:
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