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221. A 0.1539 molal aqueous solution of cane sugar (mol. mass = 342 g mol^–1) has a freezing point of 271 K while the freezing point of pure water is 273.15 K. What will be the freezing point of an aqueous solution containing 5 g of gluocose (mol. mass = 180 g mol^–1) per 100 g of solution?

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222.

An aqueous solution of 2 percent non-volatile solute exerts a pressure of 0.096 atm at the boiling poine of the solvent. What is the molecular mass of the solute ?

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223. The vapour pressure of water is 12.3 kPa at 300 K. Calculate the vapour pressure of a one molal solution of a non-volatile, non-ionic solute in water.

Solution

Step-1 what is given in problem

Vapour pressure of pure water = 12.3 kPa

We have 1 molal solution that means we have 1 moles of solute in 1kg of solvent

Step – 2 Find vapour pressure

The formula of vapour pressure when non-volatile liquid is added

Pressure = vapour pressure of pure liquid × molar fraction of liquid

P=P_(pure)X ...........1

Here we know the value of P_(pure)so need to find the value of molar fraction X

moles fraction of compound = \frac{number of moles of compounds}{total number of moles} . . . . . 2

Here we know that number of moles of solute =1 moles

And need to find the moles of solvent (water)

number of moles of water = \frac{mass of water}{molar mass of water}

And we have mass = 1 kg and 1 kg is equal to 1000g

And molar mass of water H₂O = 2×1 + 16 = 18 g/mol

Plug the value in equation (3) we get

Number of moles of water =1000 g / (18g/mol ) =55.56 moles

Plug the value in equation (2) we get

The formula of molar fraction =55.5/(55.5+1) = 0.9823

Now plug in equation (1 )we get

Partial fraction = 12.3×0.9823 = 12.08

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224. Why is the vapour pressure of a solution of glucose in water lower than that of water?

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225. A 6.90 M solution of KOH in water contains 30% by mass of KOH. Calculate the density of the KOH solution. [Molar mass of KOH = 56 g mol^–1]

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226. Give reasons for the following:
When 30 ml of ethyl alcohol and 30 ml of water are mixed, the volume of resulting solution is more than 60 ml.

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227. Give reasons for the following:
Copper is conducting as such while copper sulphate is conducting only in molten state or in aqueous solution.

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228. Urea forms an ideal solution in water. Determine the vapour pressure of an aqueous solution containing 10% by mass of urea at 40⁰C. (Vapour pressure of water at 40⁰C = 55.3 mm of Hg)

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