liquid solutions

Dilute Solutions and

Colligative Properties

• • .(6)

Chapter at a Glance

I *s\ < of < •miioiIi pivNMirc n = h x d x g . . .(1)

>• .In ii Ii is height developed in column, d is density of fluid in column at

• <|i«1111>• 11ii• i. i; is gravity.

7i oc (n/v) oc concentration . . .(2)

nV = (w/m) ST = nST . . .(3)

nit>ii< |Hr\Mire. n is mole of solute present in V litre solution, w is weight

• ii nliili ni i. mol wt. of solute S is solution constant and T is temperature in.K.

» Imiliilll. Nllllllloil 7t|=7t2 • • ' (4)

ilni '.nliili". ii<-ith<-i showing association nor dissociation)

C, = C2 . . .(5)

I 11 I iMil i IIIhllliMl of solute.

\ .i|iniii ,ii< in i ! ni luiloii with temperature: 2.303 log10— = —r-

\ R

Mini / ' , in vii|niui pressures at temperature 7\ and T2. AH is heat of

VII pi it lnutlon. MIMIIIK'N I .MW

l HI ll)|iilil LI<|ui<l systems

i•.., . . . ( 7 )

11 'i mi pic.sure of mixture and P' is partial vapour pressure of each component.

I'm '"A V,., I P'hX,, . . .(8)

IU yir

I'm '"A + p% + • • • • • .(9)

I' in i vnpoui pressure of component in pure state.

, J,,, wA^mA 0 wB /mB ^

' "' 1 wA/mA + wB /mg + . . . + ^ D w A /m A + wg/mB + . . . + ' ' '

I'm K\ (0.1'.) = P°A -^A(L.P.) • • - (11)

•V, mid XA are mole fractions in gaseous phase (G.P.) and liquid phase (L.P.)

respectively.

T l - T y

T l T 2

406 NUMERICAL PHYSICAL CHEMISTRY

For solid-liquid system

P° ~ f'a n w/m

P° n + N w/m+W/M

P° ~Pc

is relative lowering in vapour pressure.

. . .(12)

po

P°-Ps_n _wxM

P° ~N~mxW

P°-Ps _n _wxM

Ps ~ N~ mxW

(For dilute solutions) . . .(13)

(Alternative form of Raoult's law) . . .(14)

.. . . ... . . P°~Ps n wxM w x 1000 . .. . . . . Elevation in boding point: ATh ——— — — « — ^ molality . . . (15)

6 r b. p o N mxW mxW J '

Khxwx 1000 ATb = Khx molality = m x V y - . . -(16)

A7"b is elevation in boiling point and Kb is molal elevation constant of solvent.

. . . . . . P°~Pt n wxM w x 1000 Depression in freezing pomt : A7> « ——— — — « — . . .(17) r ' P° N mxW mxW

fox w x 1000

A7F=Kf x molality = m x W — • • -(18)

AT{ is depression in freezing point and K{ is molal depression constant.

RT2

* = i o o o 7

RTf2

K<=mk • • • ( 2 0 )

l{ and /v are latent heat of fusion and vaporisation in cal/g respectively.

Rll M RTb M AHy

* b = T 0 0 0 A / / T l 0 0 0 A S ; ( • • A S v = - F ) •••(22)

where A//v and ASw are latent heat of vaporisation in cal/mol and entropy change for

vaporisation in cal/mol respectively.

Abnormal Colligative Properties

For solutes undergoing dissociation :

Experimental colligative property > normal colligative property

(O.P., AP, ATb , ATf)

Experimental molecular wt. < normal molecular wt.

For solute : AxBy > xAn + yB*~

a is degree of dissociation

j > I . . .(24)

DII U 11 SOLU I ION AND COLLIGATIVE PROPLRTIES 407

Nonnal mol. wt. , i = — = 1 - a + xa + ya . . .(25)

Exp. mol. wt.

van't Hoff Coefficient (g) = - 1 — . . .(26)

(x + y)

I1 or solutes undergoing association :

Exp. C.P. < Normal C.P.

Exp. mol. wt. > normal mol. wt.

For solute : nA (A)n

• • " ( 2 7 ) Normal C.P. n

Normal mol. wl. , a oi / —— = l - a + - . . . (28)

I'.xp. mol. wt. n

n i I IISHIH nilion and n is no. of molecules undergoing association.


The Basic Problems with S o l u t i o n — —

>- Problem 1. Arginine vasopressin is a pituitary harmone. It helps to regulate the

amount of water in the blood by reducing the flow of urine from the

kidneys. An aqueous solution containing 21.6 mg of vasopressin in

100 mL of solution had an osmotic pressure of 3.70 mm Hg at 25°C.

What is the molecular weight of the harmone?

>- Problem 2. A solution is prepared by dissolving 1.08 g of human serum albumin,

a protein obtained from blood plasma, in 50.0 cm3 of aqueous solution.

The solution has an osmotic pressure of 5.85 mm Hg at 298 K.

(a) What is the molar mass of the albumin?

(b) What is the height of water column placed in solution?

d (H ? 0) = 1 g cm

>- Problem 3. The osmotic pressure of blood is 7.65 atm at 37°C. How much glucose

should be used per litre for an intravenous injection that is to have the

same osmotic pressure as blood.

>• Problem 4. At 25°C, a solution containing 0.2 g of poiyisobutylene in 100 mL of

benzene developed a rise of 2.4 mm at osmotic equilibrium. Calculate

the molecular weight of poiyisobutylene if the density of solution is

0.88 g/mL.

>• Problem 5. At 300 K, 36 g of glucose present per litre in its solution has an osmotic

pressure of 4.98 bar. If the osmotic pressure of solution is 1.52 bar at

the same temperature, what would be its concentration?

>• Problem 6. At 20°C, the osmotic pressure of urea solution is 400 mm. The solution

is diluted and the temperature is raised to 35°C, when the osmotic

pressure is found to be 105.3 mm. Determine extent of dilution.

>• Problem 7. At 27°C, a 5% solution (wt./vol.) of cane-sugar is isotonic with

8.77 g/litre of urea solution. Find m.wt. of urea, if m.wt. of sugar is

342. Also report the osmotic pressure of soiution if 100 mL each are

mixed at 27°C.

>- Problem 8. An aqueous solution of 2 per cent (wt./wt.) non-volatile solute exerts

a pressure of 1.004 bar at the boiling point of the solvent. What is the

molecular mass of the solute?

>- Problem 9. The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour

pressure of 1 molal solution of a solute in it.

>• Problem 10. Calculate the mass of a non-volatile solute (molecular mass 40) which

should be dissolved in 114 g octane to reduce its vapour pressure to

>• Problem 11. A solution containing 30 g of a non-volatile solute exactly in 90 g

water has a vapour pressure of 2.8 kPa at 298 K. Further 18 g of water

is then added to solution, the new vapour pressure becomes 2.9 kPa at

298 K. Calculate :

DILUTI SOLUTIONS AND COLLIGATIVE PROPLRTIES 409

(i) Molecular mass of the solute,

(ii) vapour pressure of water at 298 K.

Problem 12. Find the molality of a solution containing a non-volatile solute if the

vapour pressure is 2% below the vapour pressure of pure water.

• Problem 13. Dry air was successively passed through a solution of 5 g solute in

80 g water and then through pure water. The loss in weight of solution

was 2.5 g and that of pure water was 0.04 g. What is mol. wt. of

solute?

• Problem 14. Heptane and octane form ideal solution. At 373 K, the vapour pressures

of the two liquid components are 105.2 kPa and 46.8 kPa, respectively.

What will be the vapour pressure, in bar, of a mixture of 25.0 g of

heptane and 35.0 g of octane?

• Problem 15 I he vapour pressures of ethanol and methanol are 44.5 and 88.7 mm

ol 11;.'. respectively. An ideal solution is formed at the same temperature

by mixing 60 g of ethanol and 40 g of methanol. Calculate the total

vapour pressure of solution and mole fraction of methanol in vapour

phase.

• Piulili in l(> Al 110 K, the vapour pressure of an ideal solution containing 2 moles

ol I and 3 moles of B is 550 mm of Hg. At the same temperature, if

one mole of B is added to this solution, the vapour pressure of solution

increases by 10 mm of Hg. Calculate the V.P. of A and B in their pure

MlllC.

• I'M.III. IN | 1 In Ill i liiniilc water gets frozen causing damage to the radiators of

i II l ili\ I. .,.• glycol is used as an antifreeze agent. Calculate the amount

• i| etli) lenr glycol to be added to 4 kg water to prevent it from freezing

al (i"( A, for water is 1.85 K mol"1 kg.

• I 'mlib ni IN All aqueous solution of liquid 'A" (mol. weight 56) 28% by weight

has a vapour pressure 150 mm. Find the vapour pressure of 'JT if

\,ipoui pressure of water is 155 mm of Hg.

• Pnil'l.iii l'» \ '."„ solution (by mass) of cane sugar in water has freezing point of

' / I k Calculate the freezing point of a 5% glucose (by mass) in

water. The freezing point of pure water is 273.15 K.

* Problem 20 I liilylntcd hydroxytoluene (BHT) is used as an antioxidant in processed

foods (it prevents fats and oils from becoming rancid). A solution of

.5 g of BUT in 100 g of benzene has a freezing point of 4.88 K.

What is the molecular weight of BHT? A'f (benzene) = 5.12 K moP1

kg, freezing point of benzene = 5.45 K?

>• Problem 21. An aqueous solution of glucose containing 12 gin 100 g of water was

found to boil at I00.34°C. Calculate K\ for water in K m o P 1 kg.

410 NUMERICAL PHYSICAL CHEMIST HY

> Problem 22. The boiling point of CHCI3 was raised by 0.323°C when 0.37 g of

naphthalene was dissolved in 35 g CHCI3. Calculate the molecular

weight of naphthalene. K\ for CHCl3 = 3.9 K mol -1 kg.

>- Problem 23. What will be the boiling point of bromine when 174.5 mg of octa-

atomic sulphur is added to 78 g of bromine. K\ for Br2 is 5.2 K moT

' k g and b.pt. of Br2 is 332.15 K.

>• Problem 24. What is the depression in freezing point of a solution of non-electrolyte

if elevation in boiling point is 0.13 K, Kb = 0.52 K moP 1 kg;

K{= 1.86 K m o P 1 kg?

>- Problem 25. Pure benzene boiled at 80°C. The boiling point of a solution containing

1 g of substance dissolved in 83.4 g of benzene is 80.175°C. If latent

heat of vaporization of benzene is 90 cal perg, calculate the molecular

weight of solute.

>- Problem 26. Calculate the osmotic pressure of 20% (wt./vol.) anhydrous Ca(N0 3) 2

solution at 0°C assuming 100% ionisation.

>• Problem 27. The vapour pressure of a solution containing 2 g of NaCl in 100 g

water, which dissociated in one Na and one CI" ion in water, is

751 mm, at 100°C. Calculate the degree of ionisation o fNaCl .

>• Problem 28. What is osmotic pressure of the aq. solution of the given solute at

27°C if depression in freezing point is 0.93°? Molal depression

constant of water is 1.86 K mol -1 kg? Assume molality as molarity.

>• Problem 29. 17.4% (wt./vol.) K 2 S0 4 solution at 27°C is isotonic to 5.85% (wt./

vol.) NaCl solution at 27°C. If NaCl is 100% ionised, what is %

ionisation of K 2 S0 4 in aq. solution?

>- Problem 30. The partial pressure of ethane over a saturated solution containing

6.56 x 10 -2 g of ethane is 1 bar. If the solution contains 5.00 x 10"2 g

of ethane, then what shall be the partial pressure of the gas.

>• Problem 31. Calculate the concentration of C 0 2 in a soft drink that is bottled with

a partial pressure of C 0 2 of 4 atm over the liquid at 25°C. The Henry's

law constant for C 0 2 in water at 25°C is 3.1 * 10~2 mol/litre-atm.

I HI U11 SOLU1 IONS AND COLLIGATIVE PROPERTIES 411

Answers

I. 1085 g mop ' ; 2.

t 54.10 g; 4.

0.061 molar; 6.

7, 59,99,3.60 atm; 8.

«> 12.08 kPa; 10.

II (i) .M g mol ', (ii) 3.53 kPa; 12.

I», 70.31; 14.

IN, ftft I I Mim. o 144, 0.656 ; 16.

I ' HIM I 1 it , 18.

I'» , W ) 0 6 k . 20.

21 0 '»I K mol 1 kg; 22.

M H.'I 'isK; 24.

jn IM'> 72; 26.

I> M ' V 28.

.'•> 10 h »K,S0 4 ; 30.

w 0 I) mol litre 1

(a) 68655 g/mol, (b) 7.958 cm;

2.39 x 105;

4 times;

40.97 gmoP 1 ;

10 g;

1.1334;

73.08 kPa;

A = 460 mm, 5 = 610 mm;

110 mm;

224.56 g/mol;

127.6;

0.465 K;

82.0 atm;

12.315 atm;

0.762 bar;

DILUTE SOLUTIONS AND COLLIGATIVE PROPERTIES

Selected Problems with Solutions

421

>• Problem 1. If at a particular temperature, the density of 18 M H2SO4 is

1.8 g cm , calculate:

(a) Molality,

(b) % concentration by weight of solution,

(c) Mole fraction of water and H2SO4,

(d) Relative decrease in vapour pressure with respect to H2O solvent

assuming H2SO4 almost unionised at this high concentration.

> Problem 2, At 25°C, a solution containing 0.2 g of polyisobutylene in 100 mL of

benzene developed a rise of 2.4 mm at osmotic equilibrium. Calculate

the molecular weight of polyisobutylene if the density of solution is

0.88 g/mL.

> Problem 3. Calculate O.P. of a solution obtained by mixing 100 mL of 3.4% solution

(wt./vol.) of urea (m. wt. 60) and 100 mL of 1.6% solution (wtVvol.) of

cane-sugar (m. wt. 342) at 20°C.

> Problem 4. A tube of uniform cross-sectional area 1 cm is closed at one end with

semipermeable membrane. A solution of 5 g glucose per 100 mL is

placed inside the tube and is dipped in pure water at 27°C. When

equilibrium is established calculate.

(a) Osmotic pressure of solution,

(b) Height developed in vertical column,

Assume density of final glucose solution 1 g/mL.

> 1'iohlcni 5. A beaker containing 20 g sugar in 100 g water and another containing

10 g sugar in 100 g water are placed under a bell-jar and allowed to

stand until equilibrium is reached. How much water will be transferred

from one beaker to other?

> Problem 6. At 300 K, two solutions of glucose in water of concentration 0.01 M and

0.001 M are separated by semipermeable membrane with respect to

water. On which solution, the pressure need be applied to prevent

osmosis? Calculate magnitude of this applied pressure.

*• Problem 7. Al 10°C, the osmotic pressure of urea solution is 500 mm. The solution

is diluted and the temperature is raised to 25°C, when the osmotic

pressure is found to be 105.3 mm. Determine extent of dilution.

+ Problem 8. At 300 K, the vapour pressure of ah ideal solution containing one mole

of A and 3 mole of B is 550 mm of Hg. At the same temperature, if one

mole of B is added to this solution, the vapodr pressure of solution

increases by 10 mm of Hg. Calculate the V.P. of A and B in their pure

state.

> Problem 9. The vapour pressure of benzene and toluene at 20°C are 75 mm of Hg

and 22 mm of Hg respectively. 23.4 g of benzene and 64.4 g of toluene

are mixed. If two forms ideal solution, calculate the mole fraction of


benzene in vapour phase when vapours are in equilibrium with liquid

mixture.

> Problem 10. Vapour pressure of C6H^ and C7H8 mixture at 50°C are given by

P = 179 XB + 92, where XB is mole fraction of C6H6 . Calculate

(in mm):

(a) Vapour pressure of pure liquids.

(b) Vapour pressure of liquid mixture obtained by mixing 936 g C^Hg

and 736 g toluene.

(c) If the vapours are removed and condensed into liquid and again

brought to the temperature of 50°C, what would be mole fraction

of CgHg in vapour state?

> Problem 11. Ideal mixture of two miscible liquids A and B is placed in a cylinder

containing piston. Piston is pulled out isothermally so that volume of

liquid decreases but that of vapours increases. When negligibly small

amount of liquid was left, the mole fraction of A in vapour phase is 0.4.

If P°a = 0.4 atm and P% = \2 atm at the experimental temperature,

calculate the total pressure at which the liquid is almost evaporated.

>• Problem 12. A mixture of two immiscible liquids nitrobenzene and water boiling at

99°C has a partial vapour pressure of water 733 mm and that of

nitrobenzene 27 mm. Calculate the ratio of the weights of nitrobenzene

to the water in distillate.

>- Problem 13. The vapour pressure of two pure liquids A and B that forms an ideal

solution at 300 and 800 torr, respectively at temperature T. A mixture of

the vapours of A and B for which the mole fraction of A is 0.25 is slowly

compressed at temperature T. Calculate:

(a) The composition of the first drop of the condensate,

(b) The total pressure when this drop formed,

(c) The composition of the solution whose normal boiling point is T,

(d) The pressure when only the last bubble of vapour remains,

(e) Composition of the last bubble.

> Problem 14. The vapour pressure of water at 293 K is 2338 Pa and the vapour pressure •a

of an aqueous solution is 2295.8 Pa. If solution density is 1010 kg/m at

313 K, calculate the osmotic pressure at 313 K. Molecular weight of

solute = 60.

>• Problem 15. Calculate the vapour pressure of solution having 3.42 g of cane-sugar in

180 g water at 40°C and 100°C. Given that boiling point of water is

100°C and heat of vaporisation is 10 kcal mol - 1 in the given temperature

range. Also calculate the lowering in vapour pressure of 0.2 molal

cane-sugar at 40°C.

>- Problem 16. Calculate the vapour pressure lowering of a 0.10 m aqueous solution of

non-electrolyte at 75°C.

>- Problem 17. What weight of solute (M. wt. 60) is required to dissolve in 180 g of

water to reduce the vapour pressure to 4/5th of pure water?

DILUTI SOLUTIONS AND COLLIGATIVE PROPLRTIES 423

>• Problem 18. Dry air was successively passed through a solution of 5 g solute in 80

g water and then through pure water. The loss in weight of solution was

2.5 g and that of pure water was 0.04 g. What is mol. wt. of solute?

> Problem 19. What will be the boiling point of bromine when 174.5 mg of octa-atomic

sulphur is added to 78 g of bromine? for Br2 is 5.2 K mol - 1 kg and

b.pt. o f B r 2 i s 332.15 K.

>• Problem 20. An aqueous solution containing 5% by weight of urea and 10% by

weight of glucose. What will be its freezing point? Kf for H 2 0 is

1.86° mol - 1 kg.

> Problem 21. Two elements A and B form compounds having molecular formula

ABi and AB4. When dissolved in 20 g C6H6, 1 g of AB2 lowers the

f. pt. by 2.3°C whereas 1.0 g of lowers it by 1.3°C. The Kf for

CfcHg is 5.1 K mol -1 kg. Calculate atomic weight of A and B.

> Problem 22. If boiling point of an aqueous solution is 100.1°C. What is its freezing

point? Given latent heat of fusion and vaporization of water are

80 cal g - 1 and 540 cal g_ 1 respectively.

> Problem 23. Calculate the freezing point of an aqueous solution having mole fraction

of water 0.8. Latent heat of fusion of ice is 1436.3 cal mol -1 .

> Problem 24. 1000 g of 1 m sucrose solution in water is cooled to - 3.534°C. What weight of ice would be separated out at this temperature?

Kf of H 2 0 = 1.86 K mol -1 kg.

+• Problem 25. The osmotic pressure of an aqueous solution of sucrose is 2.47 atm at

303 K and the molar volume of the water present in solution is

18.10 cm . Calculate the elevation of boiling point of this solution.

Given AHvap = 540 cal/g. Assume volume of solvent equal to volume of

solution.

>• Problem 26. A dilute solution contains m mole of solute A in 1 kg of a solvent with

molal elevation constant Kb. The solute A undergoes dimerization as

2A Aj. Show that equilibrium constant for dimer formation is given

by:

k = Kb (Kf/n - ATb)

c (2A Tb-Kbm)2

where ATb is elevation in boiling point for given solution. Assume

molarity = molality.

> Problem 27. A solution containing 0.1 mole of naphthalene and 0.9 mole of benzene

is cooled out until some benzene freezes out. The solution is then

decanted off from the solid and warmed upto 353 K where its vapour

pressure was found to be 670 torr. The freezing point and boiling point

of benzene are 278.5 K and 353 K respectively and its enthalpy of fusion

is 10.67 kJ mol '. Calculate Ihc temperature to which the solution was


cooled originally and the amount of benzene that must have frozen out.

Assume ideal behaviour.

> Problem 28. One mole of (C6H5)3COH dissolved in 1000 g of 100% sulphuric aciu

lowers the freezing point of sulphuric acid twice as one mole of

CH3OH shows in 1000 g of 100% sulphuric acid. Comment on it

assuming that CH3OH is neither dissociated nor associated in sulphuric

acid.

>• Problem 29. Calculate the osmotic pressure of 20% (wt./vol.) anhydrous CaCl2

solution at 0°C assuming 100% ionisation.

>• Problem 30. A certain mass of a substance when dissolved in 100 g CfiHg lowers the

freezing point by 1.28°C. The same mass of solute dissolved in 100 g

of water lowers the freezing point by 1.40°C. If the substance has normal

molecular weight in benzene and is completely dissociated in water, into

how many ions does it dissociate in water? Kf for H2O and QH^, are

1.86 and 5.12 K mol -1 kg respectively.

>- Problem 31. The vapour pressure of a solution containing 2 g of an electrolyte BA

in 100 g water, which dissociates in one B+ and one A~ ion in water, is

751 mm, at 100°C. Calculate degree of ionisation of BA if its mol. wt.

is 56.

>- Problem 32. Vapour pressure of a saturated solution of a sparingly soluble salt

A2J33 is 31.8 mm of Hg at 40°C. If vapour pressure of pure water is 31.9

mm of Hg at 40°C, calculate KSP of A2B3 at 40°C.

> Problem 33. 1 g of mono-basic acid in 100 g of water lowers the freezing point by

0.168°. If 0.2 got" same acid requires 15.1 mLof N/10 alkali for complete

neutralization, calculate degree of dissociation of acid. K\ for H 2 0 is

1.86 K m o f 1 kg.

> Problem 34. What will be the osmotic pressure of 0.1 M monobasic acid if its pH is

2 at 25°C.

> Problem 35. A complex is represented as C0G3 • XNH3. Its 0.1 molal solution in

aqueous solution shows A7f = 0.558°. K( for H 2 0 is 1.86 K molality"'.

Assuming 100% ionisation of complex and co-ordination number of Co

as six, calculate formula of complex.

> Problem 36. The freezing point of an aqueous solution of KCN containing 0.1892

mol kg"1 was -0.704°C. On adding 0.045 mole of Hg(CN)2 , the freezing

point of the solution was -0.620°C. If whole of Hg(CN)2 is used in

complex formation according to the equation,

Hg(CN)2 JV /HKCN—> K,„ [Hg(CN),„ + 2] what is the formula of the

complex? Assume I Hg(CN),,, + 2]"'~ is not ionised and the complex

molecule is 100% ionised. K( (H20) is 1.86 kg mol"1 K.

>• Problem 37. A0.OOI molal solution ofacomplex represented as f'l(NI 1 1 1 in water

had Irre/.ing point depression of 0,(X)54°C. loi ILO I 86 K

I )ILU 11 SOLU HONS AND COLLIGATIVE PROPER IIES 425

molality '. Assuming 100% ionisation of the complex, write the ionisa-

tion nature and formula of complex.

• Problem 38. The freezing point of 0.08 m NaHS04 is - 0.345°C. Calculate the

percentage of HSO4 ions that transfer a proton to water to form S0 4

ion. Kf of H2O = 1.86 mol 1 kg. Assume HSO4 does not show hydrolysis

• Problem 39. The K$p (25°C) of- sparingly soluble salt XY2 is 3.56 xlO" 5

3 —3

mol litre and at 30°C, the vapour pressure of its saturated solution

in water is 31.78 mm of Hg. Calculate the enthalpy change of the

reaction if the vapour pressure of H?0 at 30°C is 31.82 mm. XY2 + Aq. ^ ] + 2 ) (100% ionisation)

• Problem 40. An aqueous solution of an acid is so weak that it can be assumed to be

practically unionised, boiled at 100.4°C. 25 mL of this solution was

neutralised by 38.5 mL of 1 N solution of NaOH. Calculate basicity of

the acid if Kb for water is 0.52 K mol"' kg. Assume molality equal to

molarity.

• Problem 41. The freezing point Of 0.02 mole fraction of acetic acid in benzene is

277.4 K. Acetic acid exists partly as dimer. Calculate the equilibrium

constant for dimerisation. Freezing point of benzene is 278.4 K and heat

. of fusion of benzene is 10.042 kJ moL1. Assume molarity equal to

molality.

• Problem 42. What is the ratio by weight of NaF and Nal which when dissolved in

water produces the same osmotic effects as 0.1 molar solution of urea

in water at same temperature? The weight of residue obtained on

evaporation of the salt solution is 0.48 gram per 100 mL of solution

evaporated. Assume complete dissociation of the salts.

• Problem 43. Calculate the value of molaJ elevation constant for water if

^ v a p o r i s a t i o n >s 2 6 . 3 3 cal K ~ ' mol"1.


Answers

1. (a) 500 molal, (b) 98%, (c) H2S(

2. 2.39 x l O 5 ;

4. (a) 6.842 atm, (b) 70.43 m ;

6." See solution ;

8, A = 400 mm, .8 = 600 mm ;

10. (a) 92 mm, (b) 199.4 mm, (c) l

' 11. 0.667 atm ;

13. (a) 0.47, 0.53, (b) 565 torr, (c)

14. 2.53 x 106 Pa ;

16. 0.53 mm ;

18. 70.31 ;

20. -3.04°C ;

22. -0.362°C ;

24. 352.98 ;

26. See Solution

28. See solution ;

30. 3 ;

32. 5.672 x l O - 8 ;

"34. 2.69 atm ;

36. K2[Hg(CN)4] ;

38. 31.85% ;

40. 2 ;

42. 0.28 ;

4 = 0 .9 , H 2 0 = 0 .1 , (d) 0 . 9 ;

3. 7.38 atm ;

5. 33.3 g ;

7. 5 times ;

9. 0.59, 0.41 ;

.815,0.185, (d) 0.928, 0.072 ;

12. 4 ;

0.08, 0.92, (d) 675 torr, (e) 0.889 ;

15. 759.2 mm, 0.21 mm ;

17. 150 g ;

19. 332.195 K ;

21. A = 25.59, B = 42.65 ;

23. -25.97°C ;

25. 5.145 x lO" 2 ;

27. 270.39 K , 12.14 g ;

29. 121.14 atm ;

31. 86.41% ;

33. 19.6% ;

35. See solution ;

37. See solution ;

39. 52.799 kJ ;

41. 3.39 ;

43. 0.5 K molality"1.

JfW

liquid solutions

Documents