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Solutions

Short Answer Type

211. Give one example each of miscible liquid pairs showing positive and negative deviations from Raoult’s law. Give one reason for such deviations.

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212. State Raoult’s law for solutions where only solvent is volatile. Derive a mathematical exression for this law.

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213.
State with a suitable diagram and appropriate examples why some non-ideal solutions. Show positive deviation from ideal behaviour.

In case of negative deviations from Raoult's law, the intermolecular attractive forces between A-A and B-B are weaker than those between A-B and leads to decrease in vapour pressure resulting in negative deviations. An example of this type is a mixture of phenol and aniline.

In this case the intermolecular hydrogen bonding between phenolic proton and lone pair on nitrogen atom of aniline is stronger than the respective intermolecular hydrogen bonding between similar molecules.

This decreases the escaping tendency of molecules for each component and consequently the vapour pressure decreases resulting in negative deviation from Raoult's law

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214. What is meant by abnormal mass of solute? Discuss the factors which bring abnormality in the experimentally determined molecular masses of solutes using colligative properties.

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215. State the type of non-ideality exhibited by a solution of cyclohexane and ethanol or a solution of acetone and chloroform (only one case). Give reason for your answer.

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216. Miscible liquid pairs often show negative or positive deviation from Raoult’s law. What is the reason for such deviations? Give one example of each type of liquid pairs.

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Long Answer Type

217. Define vapour pressure of a liquid. What happens to the vapour pressure when (a) a volatile solute dissolves in the liquid and (b) non-volatile solute dissolvedin it?

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218. Show graphically how the vapour pressure of a solvent and a solution in it of a non-volatile solute change with temperature. Show on this graph the boiling points of the solvent and the solution. Which is higher and why?

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219. An antifreeze solution is prepared from 222.6 g of ethylene glycol (C₂H₄(OH)₂) and 200 g of water. Calculate the molality of the solution. If the density of this solution be 1.072 g ml^–1, what will be the molarity of the solution?

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220. At 300 K, 36 g of glucose (C₆H₁₂O₆) present per litre in its aqueous solution has an osmotic pressure of 4.98 bar. If the osmotic pressure of another solution of glucose is 1.52 bar at the same temperature, what would be its concentration?

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