Short & Long Answer Question (Part-1) - Solutions Notes | EduRev

Chemistry Class 12

Created by: Mohit Rajpoot

Class 12 : Short & Long Answer Question (Part-1) - Solutions Notes | EduRev

The document Short & Long Answer Question (Part-1) - Solutions Notes | EduRev is a part of the Class 12 Course Chemistry Class 12.
All you need of Class 12 at this link: Class 12

Q.1. Define 
(i) Solute 
(ii) Solvent
Ans. 
(i) Solute - A substance which dissolves in another substance. Its state changes or it is present in smaller quantity.
(ii) Solvent - A component of solution which has same physical state as solution or which is present in larger quantity.

Q.2. Is smoke a homogeneous solution?
Ans. 
No, smoke is a colloidal solution

Q.3. Oil and water don't mix. Why?
Ans. 
Oil is a non-polar ester and water is a polar molecule. Hence, they do not mix according to like dissolves in like principle.

Q.4. Benzene is soluble in toluene but not in water. Why?
Ans. 
Benzene is a non-polar molecule. Hence it is soluble in toluene which is also non-polar but it is insoluble in water which is polar.

Q.5. Which concentration term remains unaffected by temperature?
Ans. 
Molality remains unaffected by temperature.

Q.6. Why does the molality of solution remain unchanged with temperature?
Ans. 
Because mass of solute and solvent are independent of temperature.

Q.7. Why is molality preferred over molarity of solution?
Ans. 
Because molality does not change with temperature.

Q.8. How does molarity of solution change with temperature?
Ans. 
With rise in temperature molarity decreases because volume of solution increases.

Q.9. Explain the term "mole fraction".
Ans. 
Mole fraction is the ratio of number of moles of solute or solvent and total number of moles of solution.

Q.10. Why is vapour pressure of solution of glucose in water lower than that of pure water?
Ans. When glucose is dissolved in water, some of the glucose molecules displace water molecules from the surface. Therefore, rate of evaporation of water decreases, hence vapour pressure decreases.

Q.11. Name two factors on which the vapour pressure of the liquid depends.
Ans. 

(i) Nature of liquid (intermolecular forces).
(ii) Temperature.

Q.12. State any two characteristics of ideal solutions.
Ans. 

(i) They obey Raoult's law for entire range of composition.
(ii) There is no change in volume and enthalpy of mixing

Q.13. Give an example of ideal solution.
Ans. 
Solution of benzene and toluene.

Q.14. Give an example of solution showing negative deviation from ideal behaviour.
Ans. 
Water and sulphuric acid solution show negative deviation from ideal behaviour.

Q.15. Give an example of solution showing positive deviation from ideal behaviour.
Ans. 
A solution of ethanol in water shows positive deviation from ideal behaviour.

Q.16. What type of solution is formed when chloroform is mixed with acetone?
Ans. 
When chloroform is mixed with acetone, it shows negative deviation from ideal behaviour.

Q.17. What type of solution is formed when ethanol is mixed with water?
Ans. 
When ethanol is mixed with water, the solution shows positive deviation from ideal behaviour.

Q.18. Give an example of solution which shows negative deviation from ideality.
Ans. 
Chloroform Acetone.

Q.19. Give an example of solution which shows positive deviation from ideality.
Ans. 
Ethanol + Water.

Q.20. Define azeotropic mixture.
Ans. 
A mixture of liquids which boils at constant temperature without change in composition is called azeotropic mixture

Q.21. What are minimum boiling azeotropes? Give an example.
Ans. 
A mixture of liquids which boils at a temperature lower than the boiling of both the components in pure state, e.g. Ethanol and water.

Q.22. What type of behaviour is expected when water is added to sulphuric acid?
Ans.
Water + sulphuric acid shows negative deviation from ideal behaviour,

Q.23. What is an antifreeze?
Ans.
Antifreeze is a liquid which is added to another liquid prevent its freezing at normal freezing point, e.g. Glycol in water.

Q.24. Define "colligative properties".
Ans.
Those properties which depend upon number of solute particles only and not on nature of solute are called colligative properties.

Q.25. Why does the boiling point of a solution increase on adding non-volatile solute?
Ans. On adding non-volatile solute to a liquid its vapour pressure decreases. Hence boiling point increases.

Q.26. Why does the freezing of a solution decrease on adding non-volatile solute?
Ans. 
On adding non-volatile solute to a liquid its vapour pressure decreases, hence freezing point decreases.

Q.27. On what factor does the elevation in boiling point depend?
Ans.
Number of solute particles.

Q.28. On what factors does depression in freezing point depend?'.
Ans.
Nature of liquid (intermolecular force),

Q.29. How does the boiling point of a liquid change with external pressure?
Ans. 
Boiling point of a liquid increases with increasing external pressure.

Q.30. What change is observed in boiling point of a liquid at higher altitude?
Ans. 
At higher altitude boiling point of liquid decreases.

Q.31. What is osmosis?
Ans. 
The process of flow of solvent molecules through a semipermeable membrane from a dilute solution to a concentrated solution.

Q.32. Define osmotic pressure.
Ans. 
The driving force responsible for the process of osmosis is called osmotic pressure. or the extra pressure applied on the solution side to just stop the process of osmosis, when the solvent and solution are separated by semipermeable membrane is called osmotic pressure.

Q.33. State how does osmotic pressure vary with temperature?
Ans. 
Osmotic pressure increases with increasing temperature.

Q.34. How does osmotic pressure depend upon number of moles of solute particles?
Ans. Osmotic pressure is directly proportional to the number of solute particles. at constant 'V" and 'T'.

Q.35. Doctors advise gargles by saline water in case of sore throat Why?
Ans. 
Saline water is hypertonic solution therefore fluids responsible for irritation in throat will come out.

Q.36. What is reverse osmosis?
Ans. 
Flow of solvent from solution side to solvent side separated by semi permeable membrane is called reverse osmosis. It occurs when external pressure higher than osmotic pressure is applied on the solution side.

Q.37. What is the-use of reverse osmosis?
Ans. 
Reverse osmosis is used for desalination of saline water.

Q.38. What are isotonic solution?
Ans. 
Solutions having same osmotic pressure are called isotonic 'solution.

Q.39. Define 
(i) Hypertonic Solution
(ii) Hypotonic
Ans. 
Solution having higher osmotic pressure is called hypertonic solution and that having lower osmotic pressure is called hypotonic solution.

Q.40. What is van't Hoff's factor?
Ans. 
The ratio of observed colligative properties and normal colligative property is called van't Hoff factor. It is denoted by (i).

Q.41. When is the value of van't Hoff factor more than one?
Ans. 
When solute undergoes dissociation in solution e.g. electrolytes like NaCI.

Q.42. When is the value of van't Hoff factor less than one?
Ans. 
When the solute molecules undergo association in solution Example. Acetic acid in benzene.

Q.43. Name the colligative property mostly used for the determination of molecular mass of macromolecules.
Ans. 
Osmotic pressure.

Q.44. Which will have greater boiling point 
(i) 1 M urea solution
(ii) 1 M NaCI solution
Ans. 
1 (M) NaCI solution.

Q.45. Osmotic pressure of 1 M KCl solution is higher than 1 M urea solution. Why?
Ans. 
KCl is an electrolyte, it undergoes dissociation in solution, hence number of particles increases. Urea is non-electrolyte.

Q.46. Differentiate between molarity and molality of solution.
Ans. 

(a) Molarity is the number of moles of solute dissolved in one litre solution. Molality is the number of moles of solute dissolved in one kilogram solvent.
(b) Molarity decreases with rise in temperature but molality is independent of temperature.

Q.47. Give an example each of miscible liquid pairs showing positive and negative deviations from Raoult's law. Give reasons for each such deviation.
Ans. 

(i) Mixture showing positive deviation from Raoult's law Ethanol and acetone.
Reason: Solute - solvent interaction is weaker than solute solute and solvent - solvent interactions.
(ii) Mixture showing negative deviation from Raoult's law - chloroform and acetone.
Reason: Solute solvent interaction is stronger than solute solute and solvent - solvent interaction.

Q.48. Define vapour pressure. What happens to the vapour pressure when 
(i) volatile solute dissolves in the liquid
(ii) non-volatile solute dissolves in the liquid.
Ans. 
The pressure exerted by gas molecules on its liquid layer at equilibrium is called vapour pressure.
(i) When volatile liquid is added to another liquid then the resultant vapour pressure may increase, decrease or may remain same depending on the strength of solute- solvent interaction.
(ii) Net vapour pressure decreases when non-volatile solute is added to it.

Q.49. Explain why freezing point of a solvent is lowered on dissolving a non-volatile solute in it. Give an important application of freezing point depression.
Ans. 
When a non-volatile solute is dissolved in a solvent its vapour pressure' decreases. Hence, vapour pressure of solvent and solution becomes equal at lower temperature. Application of freezing point depression - To prepare antifreeze mixture used in radiators of vehicles.

Q.50. Why dried fruits and vegetables slowly swell when placed in water? What will be the effect of temperature this process?
Ans. 
When dried fruits and vegetables are placed in water they swell due to flow of water into them by osmosis. Increasing temperature speed up the process.

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