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Why NaCl solution freezes at lower tempe...

Why NaCl solution freezes at lower temperature than water but boils at hig' er temperature ?

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On dissolving a solute in a solvent, the vapour pressure decreases. As a result, the solution freezes at a lower temperature and boils at a higher temperature.
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The vapour pressure of a solvent in a solution is lower than that of pure solvent, at the same temperature. A higher temperature is needed to raise the vapour pressure up to the atmospheric pressure, when boiling begins. However, increase is small, like 0.1 "mol"kg^(-1) aqueous sucrose solution boils at 100.05^(@)C . Sea water, an aqueous solution, which is rich in Na^(+) and Cl^(-) ions, freezes about 1^(@)C lower than frozen water. At the freezing point of a pure solvent, the rates at which two molecules stick together to form the solid and leave it to return to liquid state are equal when solute is present. Fewer solvent molecules are in contact with surface of solid. However, the rate at which the solvent molecules leave the surface of solid remains unchanged. That is why temperature is lowered to restore the equilibrium. The freezing point depression in an ideal solution is proportional to molality of the solute. Whene 250 m,g of eugenol is added to 100 gm of camphor (K_(f)=37.9) , it lowered the freezing point by 0.62^(@)C , the molar mass of eugenol is

The vapour pressure of a solvent in a solution is lower than that of pure solvent, at the same temperature. A higher temperature is needed to raise the vapour pressure up to the atmospheric pressure, when boiling begins. However, increase is small, like 0.1 "mol"kg^(-1) aqueous sucrose solution boils at 100.05^(@)C . Sea water, an aqueous solution, which is rich in Na^(+) and Cl^(-) ions, freezes about 1^(@)C lower than frozen water. At the freezing point of a pure solvent, the rates at which two molecules stick together to form the solid and leave it to return to liquid state are equal when solute is present. Fewer solvent molecules are in contact with surface of solid. However, the rate at which the solvent molecules leave the surface of solid remains unchanged. That is why temperature is lowered to restore the equilibrium. The freezing point depression in an ideal solution is proportional to molality of the solute. The freezing point iof a 5% by mass CH_(3)COOH (aq.) solutin is -1.8^(@)C . Th vasn't Hoff factor is ( K_(f) of water =1.86 )

ICSE-SOLUTIONS-EXERCISE (PART-II Descriptive Questions) (VERY SHORT ANSWER QUESTIONS)
  1. What are isotonic solutions ?

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  2. Hypotonic and Hypertonic solution

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  3. Why NaCl solution freezes at lower temperature than water but boils a...

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  4. Why does molality of a solution remains unchanged with change in temp...

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  5. Why is the cooking temperature in pressure cooker higher than that in...

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  6. Solution A is obtained by dissolving 1 g of urea in 100 g of water an...

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  7. Which of the following solutions shows positive deviation from Raoult'...

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  8. When is the value of van't Hoff factor more than one?

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  9. Give one example each when van't Hoff factor is 2 and (1)/(2).

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  10. How is that the boiling points of the following solutions in water ar...

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  11. Mention a large scale use of the phenomenona of reverse osmosis.

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  12. What is the sum of mole fractions of all the components in a three-co...

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  13. State Raoult's law for a solution of volatile liquids.

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  14. Differentiate between molarity and molality of a solution .How can we ...

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  15. What will be the nature of the solution when ethyl alcohol and water ...

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  16. What happens when blood cells are placed in pure water?

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  17. Which will have a higher boiling point, 0.1 M NaCl or 0.1 M BaCl(2) so...

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  18. The values of van't Hoff factors for KCl,NaCl, and K(2)SO(4) respectiv...

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  19. State the formula relating pressure of a gas with its mole fraction i...

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  20. In the determination of molar mass of A^(+) B^(-), using a colligative...

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