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The freezing point of a solution containing 0.2g of acetic acid in 20.0 g of benzene is lowered by 0.450C. calculate the degree of association of acetic acid in benzene. (Kf for benzene =5.12K kg mol-1)


Mass of CH3COOH =60g/molobserved molecular mass = Kf xWb x1000Tf x WA             =5.12 x 0.2 x100020 x0.45 =113.8g mol-1Acetic acid associates as:2CH3COOH  (CH3COOH)       1                            0    1-α                    α/2No . of particles after association = 1-α+α2 =1-α2We know that  No. of particels after association No. of partcles before association  =Normal molecular mass Observed molecular massor                       1-(α/2)1 =60113.6solving  α =0.945therefore degree of association =94.5%

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Calculate molarity and molality of 13% solution (by weight of sulphuric acid. Its density is 1.020 g cm–3. (At. mass, H = 1,16, S = 32 amu).

Answer:

13 % of solution of sulphuric acid contains 13 g of H2SO4in 100 g of the solution. Weight of water = 100 - 13 = 87 g.

mole of H2SO4 = 13/98 mole

Volume of H2SO4 solution + Weight of soluton / Density = 100/1.02 ml

= 100 / 1.02 x 1/1000 = 1/1.02 litre

Molarity of H2SO4 solution = mole of H2SO4 / Volume of solution

= 13/98 / 1/1.02 = 10.2 x 13/98 = 1.353 M

Molality of H2SO4 solution = mole of H2SO4 / wt of water in kg. = 13/98 / 87/1000 = 13/98 x 1000/87

= 1.525 mol kg-1 (mole Kg-1)

 

 

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Calculate the amount of ice that will separate out on cooling a solution containing 50g of ethylene glycol in 200g water -9.30C (Kf for water =1.86K kf mol-1).


we know that Tf =Kf xWBx 1000MB xWAGiven that WB =50gTf =9.3Kf =1.86 K kgmol-1MB =62WA =?9.3 =1.86 x50 x 100062 x WAWA =161.29 gHence aamount of ice separated from 200g water = 200-161-29 =38-71g

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What will be the boiling point of bromine when 87.25 x 10-3 g of Sulphur is added to 39g of bromine? Bromine boils at 332.15K [Kbfor Br2 -5.2K kgmole-1]


We know that Tb =Kb xWB x1000MB xWAgiven ;Kb =5.2K kg mole-1WB =87.25 x10-3gMB =256WA =39gTb =5.2 x 87.25 x 10-3 x 1000256 x 39 =0.045Boiling point of solution = 332.15 +Tb =332.15 +0.045 =332.195K

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The value of Kf for water is smaller than its Kb

A.

True


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