Chapter 2
Solutions Solutions SECTION - A
School/Board Exam. Type Questions Very Short Answer Type Questions : 1.
What Wh at is th the e phy physic sical al sta state te of so solv lven entt in Na2SO4 10H2O(s)?
Sol. Solid 2.
Ident ntif ify y solv lve ent in in Na2SO4 10H2O(s).
Sol. Na2SO4(s) 3.
In mo mois istt air air so solv lven entt is is …… ……… .
Sol. Air (Gas) 4.
What is the the effec effectt of tem tempera perature ture on the the molal molality ity of a solu solution tion? ?
Sol. No effect 5.
If (molar mass)obs = (molar mass) calc. and if the solvent is water then predict whether the solute is electrolytic or non-electrolytic.
Sol. Non-electrolyte 6.
Can we we say that for for non-electro non-electrolytic lytic solutes solutes observ observed ed v.p. v.p. of solutio solution n is equal equal to to its calcula calculated ted value? value?
Sol. No, solute may associate. 7.
For rev revers erse e osmos osmosis is how how much much pre pressu ssure re shou should ld be be appli applied? ed?
Sol. Greater than osmotic pressure. 8.
Which Whic h type type of solute solutes s show show colliga colligativ tive e propert properties ies,, volatile volatile or or non-vo non-volat latile? ile?
Sol. Non-volatile 9.
G)sol for a non-ideal solution? What is is the si sign of ((
Sol. Negative 10.. Wh 10 What at is th the e sig sign n of of ( (S) for ideal solutions? Sol. Positive Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Tower, Plot No.-4, Sector-11, Sect or-11, Dwarka, New Delhi-75 Ph.011-47623456
12
Solutions
Solution of Assignment (Set-1)
Short Answer Type Questions : 11.
What is sign of Hmix, Vmix and Gmix for ideal solution?
Sol. Hmix = 0, Vmix = 0, Gmix < 0 12. Name same concentration terms which are independent of temperature. Sol. Molality, mole fraction, mass percentage. 13. In a solution with positive deviation v.p. of solution is greater than v.p. of pure solvent. Explain. Sol. See text, graphical representation. 14. In a solution with negative deviation v.p. of solution is less than v.p. of pure solute. Explain. Sol. See text. 15. R–COOH dimerises in benzene upto 50% and it ionises upto 10% in water. Determine ratio of van’t Hoff factors in dimerisation versus ionisation.
Sol.
i1 i2
2 ⇒ 1 0.1 2 0.1 1.1 1 0.5
0.5
0.75
i1 i2
0.75 1.1
16. For two solvents Kf is 2 and 8 respectively, which one will be preferred in a depression of freezing point method and why? Sol. Second one, greater the K f easier will be measurement. 17. From 2 L 0.1 M aq. solution of sugar 0.5 L water is evaporated, determine final concentration of solution in molarity. Sol. 2 × 0.1 = 1.5 M
M
0.2 1.5
2 15
18. On dilution or on concentration of a solution what does not change? Sol. Moles of solute 19. As per Dalton's law of partial pressure how to represent vapour pressure of a solution? Sol. psol. = p A + p B 20. A solution with both volatile components is boiled and condensate is collected in another vessel, which component will be major and why? Sol. Component with greater volatility. o 21. If p A 400 mm Hg, pBo 360 mm Hg , x A = 0.8, determine x B and psol.
Sol. xB = 0.2 psol. = 400 × 0.8 + 360 × 0.2 = 80(5 × 0.8 + 0.9) = 80 × 4.9 = 392.0 22. With reference to question 21, determine vapour phase composition in equilibrium with solution. Sol.
x A
400 0.8 392
320 392
0.816 ;
xB = 0.1836
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Solution of Assignment (Set-1)
Solutions
13
23. Henry's law constant for CO2 in water is 1.67 × 10 8 Pa. Calculate amount of CO 2 in a 500 ml soft drinks bottle packed at 2.5 atm pressure of CO 2 at 298 K. Sol. xCO 2
p
KH
2.5 105 1.67 108
nCO in 500 ml 2
2.5 10 3 1.67
2.5 500 10
3
1.67 18
0.042
24. Determine osmotic pressure of an aqueous solution containing 25 g K 2SO4/L at 25°C. 25 39 2 96 0.0821 298 Sol. 3 1
3 25 174
0.0821 298 10.54
atm
25. What happens when a plant cell is placed in a (i) hypertonic solution (ii) hypotonic solution? Sol. (i)
It will shrink
(ii) It will expand
26. Doctors advises patients of high blood pressure to take less quantity of common salt, why? Sol. Osmotic pressure increases. 27. A decimolar solution of K4[Fe(CN)6] is 75% dissociated at 27°C. Determine its osmotic pressure in atmosphere. Sol. = (1 – 0.75 + 5 × 0.75) × 0.1 × 0.0821 × 300 = 4 × 0.1 × 8.21 × 3 = 9.85 atm 28. Determine mass of bi-phenyl dissolved in 100 g benzene if rise in boiling point is 2.3. Kb(benzene) = 2.57 K kg mol –1. m
Sol.
2.3
2.57
77 2 100
2.57
m 77 2
1000 100
1000
m
2.3 77 2 2.57 10
13.78 g
29. Henry's law constant for the solubility of N2 in water at 25°C is 10 5 atm and air is supposed to be 1 : 4 mixture of O2 and N2. Determine the number of moles of air dissolved in 1 mole water at 5 atm pressure. Sol. pN 5 2
xN
2
4 5
xN 105 2
5
4 10
30. Tf for 0.002 m aq. solution of Co(NH 3)5(NO2)Cl is 0.00732°C. Determine number of ions produced per molecule in aq. solution. (Kf = 1.86 K kg mol –1) Sol. 0.00732 = i × 1.86 × 0.002 i = 1.97 2 ions/molecule = 2 Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
14
Solutions
Solution of Assignment (Set-1)
Long Answer Type Questions : 31. What is the need and applicability of van’t Hoff factor? Explain the conditions where Tb = K b m can be used. Sol. See text. 32. Explain the conditions where Tb = i K bm should be used to set correct results. Sol. In case of association or dissociation of solutes. 33. Define and relate the terms volatility, vapour pressure and boiling point. Sol. See text. 34. Give graphical representation for both types of non-ideal solutions. Sol. See text. 35. Give introduction of reverse osmosis, make labelled diagram for purification of water by this method. Sol. See text. 36. 10 g of NaOH is added to 50 mL of 0.1 M aqueous solution and volume is finally made 100 ml. Calculate the molarity of resulting solution. Sol. 2.25 M 37. Mention characteristics of an ideal solution. What causes them to be non-ideal, discuss in detail. Sol. See text. 38. After removing the shell of egg, one is placed in distilled water while the other is placed in saturated solution of NaCl. What will you observed and why? Sol. Egg in water will swell while that in NaCl will shrink because of osmosis. 39. Calculate osmotic pressure of 0.1 M dibasic strong acid of pH = 4 at 27°C. Sol.
H2 A 0.1(1 ) pH = 4
2H A 2
0.2
0.1
–log[H+] = 4 [H+] = 10–4 = 0.2
= 5 × 10–4 = (1 – 5 × 10 –4 + 3 × 5 × 10 –4) × 0.1 × 0.0821 × 300 = (1 + 10 –3) × 0.0821 × 30 = 2.46 atm 40. Calculate boiling point of solution containing 30 g urea and 38 g thiourea in 800 g chloroform. Boiling point of chloroform = 61.2°C, K b = 3.63 K kg mole –1.
30 38 1 1000 60 76 3.63 T 61.2 3.63 Sol. b 1 800 800 1000 Tb = 65.73°C 41. Mention the conditions in which a solute becomes solvent and solvent becomes solute. Sol. Component of greater mass % is solvent. 42. What is molal elevation constant? What are its units? Sol. Molal elevation constant is the elevation in boiling point when molality of solution is 1. Unit of Kb = K . kg mol –1 Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
Solution of Assignment (Set-1)
Solutions
15
43. 1 mole A2 is dissolved in 1 mole solvent (polar), in another case 1 mole A +B– is added to 1 mole same solvent. Determine mole fraction of solvent in both the cases. 1 1 , x(solvent ) 2 3
Sol. (x solvent )1
2
44. In 10 L water 1 mole of Ca(OH)2 is added with 1 mole of H 2SO4. Determine van’t Hoff factor (i) of final solution. Sol. Ca(OH)2 H2 SO4
CaSO4 2H2 O
van’t Hoff factor for CaSO 4 = 2 45. 1 mole urea and 1 mole NaCl are added to water. K f = 1.86, Kb = 0.52 (ln K kg mole –1) determine the ratio of Tb vs Tf for the solution (Urea : NaCl). Sol. Tb Tf
3
0.52
2 3
1.86
2
Tb Tf
0.52
1.86
2
…(i)
w 2
…(ii)
w
26 93
SECTION - B
Model Test Paper Very Short Answer Type Questions : 1.
What is the meaning of 0.1 m solution? 0.1 mole of solute/kg of solvent
Sol. 0.1 m 2.
Under what conditions a solution shows negative deviation?
Sol. When (psol)obs < (psol)cal 3.
What are isotonic solutions?
Sol. For which osmotic pressures are equal. 4.
State Raoult's law for volatile solutes and for non-volatile solutes.
Sol.
psol
poA x A pBo xB (for volatile solute and solvent)
psol
poA x A
5.
(for volatile solvent and non-volatile solute)
Show that relative lowering of vapour pressure is equal to the mole fraction of non-volatile solute.
Sol. Vapour pressure of solution containing non-volatile solute pS = p° and
or
p
S
p
1
solvent pS
1 solvent
p
S
p p p
solvent
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16
Solutions
Solution of Assignment (Set-1)
Short Answer Type Questions : 6.
Distinguish between ideal and non-ideal solutions.
Sol. The solution which obey Raoult’s law at all concentration are called ideal solution.
p
A poA BpBo
S
Solution which do not obey Raoult’s law are called non-ideal solution. These solutions are of two types. (i) Solution showing positive deviation S
p
A poA BpBo
(ii) Solution showing negative deviation S
p
7.
A poA BpBo
Explain azeotropic solutions.
Sol. The solution whose components cannot be separated by fractional distillation are called azeotropic solution. 8.
Why constant boiling mixtures behave like one single component?
Sol. Constant boiling mixture or azeotropic solution have same mole fraction of component in liquid state and in the vapour phase so their composition remain same upon distillation. 9.
Define colligative properties.
Sol. Those properties of dilute solution which depends upon number of particles instead of nature of particles are called colligative properties. 10. Define osmosis and the conditions for isotonic solutions. Sol. Osmosis is spontaneous flow of solvent molecules from a solution of lower concentration to higher concentration, when both are separated through a SPM. Isotonic solutions have same osmotic pressure, it means under similar conditions of temperature and pressure both solution must have similar concentration. Short Answer Type Questions : 11.
Vapour pressure of dilute aq. solution of urea is 740 mm Hg at 373 K. Calculate (i) molality and (ii) x solute. 760 740
Sol.
760
molality
nurea nurea
nH O
xurea
2 76
1 38
2
1 37 18 10
3
1000 37 18
500 333
12. Decimolar solution of K4[Fe(CN)6] dissociates by 60% at 27°C. Determine osmotic pressure in N/m 2. Sol. = iCRT Calculation of i
K H Fe CN 6 1
Fe CN 6 4
4K
4
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Solution of Assignment (Set-1)
Solutions
17
i = 1 – + 4 + = 1 + 4 = 60% = 0.6 i = 1 + 4 × 0.6 = 3.4
= 3.4 ×
1 10
× 0.08 × 300
= 2.82 bar = 2.82 × 10 5 Nm –2 13. What is van’t Hoff factor? Derive it for non-ideal solutions. Sol. Van’t Hoff factor is correction term which is used to calculate number of particle actually present in the solution, if solute is undergoing association or dissociation. i = 0 for non-electrolyte and it is i > 0 for solute undergoing dissociation and i < 0 for solute undergoing association. 14. Why molar mass observed on the basis of colligative properties become abnormal in some cases? Sol. In some cases solute may undergo dissociation or association so number of particles in the solution may be different from ideal value in such cases abnormal molecular masses are observed. 15. Differentiate between the terms molarity and molality. Sol. Molarity is number of moles of solute in one litre solution and can be calculated
M=
nsolute Vol.of solution(L)
Molarity is number of moles of solute in one kg of solvent
m=
nsolute mass of solvent(kg)
16. 200 ml 0.1 M K2SO4 is added with 300 ml 0.2 M KCl. Determine molar concentration of K + in solution. Sol. [K ]
2 0.1 2 00 0.2 300 100 2(0.2 0.3) 0.2 500 100 5
17. 180 g glucose is dissolved in 1 kg water, determine the boiling temperature. (K bH2O = 0.52) Sol.
Tb 100
1 0.52
180 / 180 1
Tb = 100.52°C 18. Arrange the following aq. solutions in increasing order of their freezing points (i)
0.1 M KCN
(ii) 0.2 M Na2SO4
(iii) 0.3 M urea
Sol. (Tf )1 = 2Kf × 0.1, (Tf )2 = 3Kf × 0.2, (Tf )3 = 1 × K f × 0.3 (Tf )1 < (Tf )3 < (Tf )2 (Tf )2 < (Tf )3 < (Tf )1 Aakash Educational Services Pvt. Ltd. - Regd. Office : Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-75 Ph.011-47623456
18
Solutions
Solution of Assignment (Set-1)
Long Answer Type Questions : 19. Solution of A and B with mole % of A as 20 is made. If mole % of A in vapour phase of solution in equilibrium o o with the solution is 60, then calculate p A /pB .
Sol.19. x A
psol
pBo 0.8
xB
o 0.2 p A
psol
o p A o B
p
0.6
0.4
o p A
pBo
0.6 psol 0.2
0.4 psol 0.8
6 1
20. Discuss in detail the solubility of a solid in liquid, also discuss factors influencing the solubility and effect on vapour pressure. Sol. See text
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