F 1 Mark Questions Multiple Choice Questions yo Ti iting point tropic mixture of two liquids has a boiling tater tha either ofthe two Tiquids when it CRSE 2023 (@) shows large negative deviation from Raoult’ law (b)shows no deviation from Raoutt’s law (6) shows large positive deviation from Raoult's law (@obeys Raoult's law 2. 1 mole of liquid A and 2 moles of liquid B make a solution having a total vapour pressure 40 torr. The vapour pressure of pure A and pure B are 45 torr and 30 torr respectively. The above solution CBSE 2023 (a) is an ideal solution () shows positive deviation (©) shows negative deviation (@ is a maximum boiling azeotrope 3. Identify the law which is stated as (CBSE SQP 2021-22 (Term-t) “For any solution, the partial vapour pressure of each ‘volatile component is directly proportional to its mole fraction." (a) Henry's law (©) Dalton's law (&) Raoult's law (@) Gay-Lussac’s law 4, An azeotropic solution of two liquids has a boiling point higher than either of the two when, it (CBSE 2021-22 (Term: (a) shows a negative deviation from Raoult's law (b) shows a positive deviation from Raoult's law (©)is saturated (d) shows no deviation from Raoult's law 5. When | mole of benzene is mixed with I mole of toluene. The vapours will contain (Given : Vapour of benzene = 12.8 kPa and vapour pressure of toluene =3.85 kPa). CBSE SQP 2021 (@) equal amount of benzene and toluene as it forms an ideal solution (b)unequal amount of benzene and toluene as it forms a non-ideal solution (higher percentage of benzene (@)higher percentage of toluene Assertion-Reason 6. Assertion (A) Nitric acid and water form, maximum boiling azeotrope, CBSE SQP 2021, 13, Define azeotropes, Reason (R) Azcotropes are binary mixture havi same composition in liquid and vapour phase. (a) Both (A) and (R) are correct and (R) is the correct explanation of (A). (b) Both (A) and (R) are correct but (R) is not the correct ‘ing the explanation of (A). (©) (A) is correct and (R) is incorrect. (@) (A) is incorrect and (R) is correct. Very Short Questions 7. Define an ideal solution and write one of characteristics. CBSE 2024, 2014 Or Define ideal solution. Ail India 2013, 2012; Del i 2010C 8. Some liquids on mixing form azeotropes. What are azeotropes? Delhi 2014 Or Define the term azeotrope. All india 2013 9. State Raoult’s law. Foreign 2012 Or Define Raoult’s law in its’ general form in reference to solutions. Delhi 2011; All India 2011 Or State Raoult’s law for a solution of volatile liquids. Delhi 2010¢ 2 Marks Questions 10. What type of deviation from Raoult's law is shown by a ture of ethanol and acetone ? Give reason. ‘CBSE 2024, 2023 11. The vapour pressure of pure liquid X’ and pure liquid Y at 25°C are 120 mm Hg and 160 mm Hg respectively. If equal moles of X and Y are mixed to form an ideal solution, calculate the vapour pressure of the solution. CBSE 2023 12. On mixing liquid X and liquid Y, volume of the resulting solution decreases. What type of deviation from Raoult’s law is shown by the resulting solution ? ‘What change in temperature would you observe after mixing liquids X and ¥? CBSE 2023 What type of azeotrope is formed ion from Raoult’s law? Give an Foreign 2015, 2023 Or Define azeotropes. What type of azeotrope is formed by positive deviation from Raoult’s law? Give an example, Delhi 2015 by negative deviati example,solutions 14 State Raoul’s law fora solution containing volatile components: What is the similarity between Raoult’ y's law? Dethi 2020, Dethi 2014 45, What type of azcotropic mixture will be formed by a solution of acetone and chloroform? Justify on the basis of strength of intermolecular interactions that develop in the solution, ‘All india 2019 46, State Raoult’s law for a solution containing volatile components, Write two characteristics of the solution which obeys Raoult’s law at all concentrations. Delhi 2019 417, Write two differences between an i i non-ideal solution. Reeere tana 48, Why a mixture of carbon disulphid tone st positive deviation from Raoult’ Taw? What ype . azeotrope is formed by this mixture? CBSE 2018 ¢ 419, Define the following. (Ideal solution i) Molarity (4) Dethi 2017 20. (i) Gas (A) is more soluble in water than gas (B) at the same temperature. Which one of the two gases will have the higher value of Ky, (Henry's constant) and why? (ii) In non-ideal solution, what type of deviation shows the formation of maximum boiling azeotropes? All India 2016 21, What is meant by negative deviation from Raoult’s law? Give an example. What is the sign of A pax 7 for negative deviation? Foreign 2015 22, What is meant by positive deviation from Raoult’s law? Give an example. What is the sign of A yay 1 for positive deviation? Dethi 2015 23, Non-ideal solutions exhibit either positive or negative deviations from Raoult’s law. What are these deviations and why are they caused? Explain with one example for each type. "Al India 2011, 2010; Delhi 2010; Foreign 2010 24, State Raoult’s law for a solution containing volatile components. How does Raoult’s law become a special cease of Henry's law? All india 2013 25. Explain why a solution of chloroform and acetone shows negative deviation from Raoult’s law? ———_Dethi 2011 3 Marks Question 26, The vapour pressure of pure liquids A and B are 450 mm and 700 mm of Hg respectively at 350K. Find out the composition of the liquid mixture if total vapour pressure is 600 mm of Hg. Also, find the composition in the vapour phase. {At india 20136 5 Marks Question 27. (i) What type of deviation from Raoult's law is expected when phenol and aniline are mixed with ‘each other? What change in the net volume of the mixture is expected? Graphically represent the deviation. (i) The vapour pressure of pure water at a certain temperature is 23.80 mm Hg. If | mole of a non-volatile non-electrolytic solute is dissolved in 100 g water, calculate the resultant vapour pressure of the solution. ese Sar 2024 4. (a) Shows large negative deviation from Raoutt's law. 1 2. (c) The mole fraction of ACY 4)= 755-053 2 0.66 Mole fraction of BG 2) 3 ita + Poke (45 x0.03) +30% 0.66 33 +19.8= 21.13 torr Pr= But the total pressure py=30 torr pr (caleulated) < pr (given) Thus, it shows negative deviation. 3. (b) Given law is Raoult’s law. According to the statement, PEL p°= partial vapour pressure of component in pure state. 4. (a) The solution which shows a large negative deviation from Raoult’s law has lower vapour pressure of each component than the predicted vapour pressure. ‘Also, the total vapour pressure of solution is lower than the total vapour pressure of ideal solution. Hence, theye moos se scantsty two liquids boils at a higher 12, On mixing liquids X and Y, the volume of resulting solution decreases means itis negative deviation from Raoult's law. In this case, the temperature of the solution. tropic mixture of fenparttze than cither of them, is with | mole of ‘hen 1 male of benzene is mixed with Seance vapours wll contain higher percentage of fie co te team Vapo sssure of benzene is greater than Is a rere of te 13, Azcotropes Refer to solution 8. " a, ‘ is Azeotropes showing negative de fr " ; he solution majorly consist of zeotropes showing negative deviation from Rao Soe eae ane law form maximum boiling zeotropes ata speci * palais composition. e.g, Azeotrope formed from nitric ns 6. (b) Nitric acid and water form maximum boiling, rae aaa 8 Pe tic acid azeotropes This solution shows large negative Azstopes shoving postv eit fom Ray — Jaw form minimum boiling azeotropes at a specific Thus, both (A) and (R) are correct and (R) is not the composition, e.g, Ethanolewater mittee. Saale 14, Refer to text on page 7. 15, The mixture of acetone and chloroform is an example of maximum boiling azeotrope. It shows negative deviation from Raoult’s law because of increas increases 0 7. The solutions which obey Raoult’s law over the entire range of concentration are known as ideal solutions. For ideal solutions, AH (mixing) =Oand AV (mixing) =0, e.g. solution of n-hexane and mheptane, intermolecular forces of attraction between acetone bromoethane and chlorocthane, etc. and chloroform, since they form hydrogen bonds In these solutions (binary solutions), A—B_ type (ie. between them. solut-solvent) interactions are nearly equal o the Rei : . Raoull’s law states that, “at a given temperature, 4—A (solute-solute) and B—B type ne een si per : for a solution of volatile liquids, the partial vapour . (solvent-solvent) interactions. pressure of each component of the solution is directly 8. Azeotropes are binary mixtures having the same proportional to its mole fraction present in the composition in liquid and vapour phase and boil at solution”, constant temperatures, @ The solutions which obey Raoult’s law over the entire 9. Raoult’s law For a solution of volatile liquids, the Tange of concentration are known as ideal solutions. (1) Partial vapour pressure of each component of the The important properties of these solutions are solution is directly proportional to its mole fraction present in solution. Thus, for any component, partial * the enthalpy of mixing of pure components to form ba ao the solution is zero, ie. A nig H pet 2+ pay * the volume of mixing is also zero, ie. A mi,¥ =0. (1) where, p°is the vapour pressure of pure component 17. —_____ and 7 is the mole fraction of that component. Heal sotation aca soit 10. The mixture of ethanol and acetone shows positive ces ofthis The components ofthis e deviation from Raoult's law. As in ethanol the Taw ataltenperatuce eqn ion noob Rac imolecules are hydrogen bonded and concentration, pegave devas fos Thus, when acetone is added then its molecule get in Raoult’ aw. between the molecule of ethanol by breaking the ie. Pa # PLA hydrogen bonds, WP #73 o iy droge a aetes_ 11. Given, vapour pressure of pure liquid X = 120 mm Hg (On mixing, there is no On mixing, there is enthalpy a enthalpy and volume and volume change, ie. Narita a Y =160 mm Hg. change. hednie =O ApH #0and dpi #0 (0) foles and Y are equal, And Aix 1 1 — — Pr =5*1204> x160=60+80 18. Refer to text on page 7, o =140mm Hg Carbon disulphide and acetone form minimum boiling azeotropes, oSolutions 19. (i) Ideal solution Refer to solution 7, o Gi) Molarity (Af) Molarity is defined as the number of moles of solute dissolved in one litre or one cubic decimetre of the solution. Moles of solute Volume of solution in Titres €-8. 0.25 mol L~ (or 0.25 M) soluti . ion of NaOH means that 0.25 mole of NaOH has been dissolved in one litre (or one cubic decimetre) of solution. (1) 20. Solubility is inversely proportional i i See amversely proportional to Ky, i Henry's (@ Greater the value of Ky, lower is the solubility of the gas. As gas (4) is more soluble in water than gas (B) at the same temperature, hence the gas (A) has lower value of Ky. In other words, gas (B) has higher value of Ky, than gas (4) at the same temperature. o Gi) In non-ideal solutions, the solutions that show Motatity = large negative deviation from Raoult’s law form maximum boiling azeotropes. e.g. Mixture of nitric acid and water. o 21, Negative deviation Refer to sol. 23. o The plot showing negative deviatior Vapour pressure of solution Vapour —+ preseure noe0. Nolo tigcion t=! mie 2-0 plot for nomial soko showing negthe devon «t) 22. Positive deviation Refer to sol. 23. w ‘The plot for non-ideal solution showing positive deviation is Vapour pressure of solution popitP2 Pt for non-idea! solution showing positive deviation (4) 23, For non-ideal solutions, vapour pressure is either higher or lower than that predicted by Raoult’s law. If it is higher, the solution exhibits positive deviation and if itis lower, it exhibits negative deviation from Raoult’s law. In case of positive deviation, A—B interactions are weaker than A—A and B—B interactions. Due to this, ‘vapour pressure inereases which results in positive deviation, e.g. Ethanol ~ Acetone and Carbon disulphide — Acetone show positive deviation. For positive deviation, AH (mixing) = Positive In case of negative deviation, A—B interactions are stronger than A—A and B—B interactions. Due to this, vapour pressure decreases which results in negative deviation. e.g. Phenol + Aniline and Chloroform + Acetone show negative deviation. For negative deviation, AM (iit 24, Raoult’s law Refer to solution 14. o Raoult’s law as a special case of Henry’s law In the solution of a gas in a liquid, one of the components is so volatile that it exists as a gas and its solubility is given by Henry’s law, which states that, paKyh. partial pressure of the volatile component (gas) is, directly proportional to the mole fraction of that component (gas) in the solution. ‘When the equations of Raoult’s law and Henry's law are compared, it can be seen that the partial pressure of the volatile component or gas is directly proportional to its mole fraction in solution. Only the proportionality constant K,, differs from p® Hence, Raoult’s law and Henry's law has been {identical except that their proportionality constants are different. Therefore, Raoult’s law becomes a special case of Henry’s law in which Ky, becomes equal to vapour pressure of pure component p®. w 25. Negative deviation means A—B interactions are stronger than A—A and B—B interactions. ‘A mixture of chloroform and acetone forms a solution which shows negative deviation from Raoult’s law because chloroform molecule forms H-bonding with acetone molecule. ing) =Negative12> 26. is chloroform and solvent is acetone. Asa Heres ig nteractons becomes stronger than A—Aand B—B interactions, This decreases the Excaning tendency of molecules for each component ‘which leads to the decrease in vapour pressure and Tesulting in negative deviation from Raoult’s law. 5 HCL we * Sto. HC ge HC i, ae SC doen toning Given, p? = 450mm of Hg pep =700 mm of Hg ; Pita: =600mm of Hex « =? According to Raoult’s law, Parta* Pa Pa =Xe* Pe =O-2a)PS Prat = Pa * Pa =Ka* PULA Ps Pat(P'4- P's ha wo (On substituting the given values into the above equation, we get 600 = 700+ (450-700), , 100=250%, => %4 = 040 Thus, the composition of the liquid mixture will be 2X4 =040 Xp =1-040=060 o Calculation of composition in the vapour phase, Pa =%4% p% =040% 450 mm of Hg =180mm of Hg 060 700 mm of Hg = 420mm of Hg Mole fraction of 4 in the vapour phase Pa Pa*Po __180 “180+ 420 Pe =XeP 27. (i) The negative deviation is expected when phenol vw ____— Chopterwise CBSE Question Bonk: CHEMISty Mole fraction of & in the vapour phase =1-030=070 7 and aniline are mixed with each other. The net volume of the mixture will decrease, (AV =0) dye to stronger intermolecular interactions, 'P.1.dlagram for solutions showing negate deviation from Raoutt's low a» Gi) Vapour pressure of pure water =2380 mmHg Amount of non-volatile electrolyte solute =1 mol Amount of water = 100g ‘We know, relative lowering of vapour pressure °—p) =P wy = P * and =n, =01 nm, =100/18=555 i #4 fe ] mtn OL =—— =0018 365, p°=238mmHg Relative lowering of vapour pressure 23.8-p = =0018 238 2380- p=0428 p=238-0.428 =2337 mmHg aw