Solutions
- Which of the following aqueous solution will exhibit highest boiling point? Answer: 3. 0.01M Na₂SO₄ Key idea: elevation of boiling point depends on i× c . Urea: 1×0.01=0.01 . KNO₃ : 2×0.01=0.02 . Na₂SO₄ : 3×0.01=0.03... 1
- Match List - I with List - IIList-I (Example): A. Humidity B. Alloys C. Amalgams D. SmokeList-II (Type of Solution): I. Solid in solid II. Liquid in gas III. Solid in gas IV. Liquid in solidChoose the correct answer from the options given below : Answer: 2. A-II, B-I, C-IV, D-III Key idea: name the dispersed substance and the medium for each example. Humidity: water droplets/vapour in... 1
- 5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution? Answer: 2. The solution shows negative deviation. Key idea: compare the observed vapour pressure with the Raoult's law value. x_X=5/15=1/3 ,... 1
- The plot of osmotic pressure () vs concentration (mol L^-1) for a solution gives a straight line with slope 25.73 L bar mol^-1. The temperature at which the osmotic pressure measurement is done is:(Use R = 0.083 L bar mol^-1 K^-1) Answer: 2. 37 ^° C Key idea: Π=CRT , so the slope of Π vs C is RT . T=25.73/0.083=310\ K=37^°C Option 2. (310 is in kelvin, not ^° C, so opt... 1
- In one molal solution that contains 0.5 mole of a solute, there is Answer: 3. 500 g of solvent Key idea: molality = moles of solute per kg of solvent. 1\ m=0.5/w with w in kg gives w=0.5 kg =500 g of solvent... 1
- The correct option for the value of vapour pressure of a solution at 45^° C with benzene to octane in molar ratio 3 : 2 is :[At 45^° C vapour pressure of benzene is 280 mm Hg and that of octane is 420 mm Hg. Assume Ideal gas] Answer: 3. 336 mm of Hg Key idea: Raoult's law for an ideal solution: P=x₁P₁^°+x₂P₂^° . x_benzene=3/5=0.6 , x_octane=2/5=0.4 . P=0.6(280)+0.... 1
- The following solutions were prepared by dissolving 10 g of glucose (C_6H_12O_6) in 250 ml of water (P_1), 10 g of urea (CH_4N_2O) in 250 ml of water (P_2) and 10 g of sucrose (C_12H_22O_11) in 250 ml of water (P_3). The right option for the decreasi… Answer: 1. P₂ > P₁ > P₃ Key idea: for equal mass in equal volume, osmotic pressure π=CRT is proportional to moles, i.e. inversely proportion... 1
- The right option for the statement "Tyndall effect is exhibited by", is : Answer: 3. Starch solution Key idea: the Tyndall effect needs colloidal particles large enough (1 to 1000 nm) to scatter light. Starch forms... 1
- The freezing point depression constant (K_f) of benzene is 5.12 K kg mol^-1. The freezing point depression for the solution of molality 0.078 m containing a non-electrolyte solute in benzene is (rounded off upto two decimal places) : Answer: 3. 0.40 K Depression in freezing point: Δ T_f=K_f m . Δ T_f=5.12×0.078=0.399≈0.40\ K Option (3) is correct. 1
- A mixture of N_2 and Ar gases in a cylinder contains 7 g of N_2 and 8 g of Ar. If the total pressure of the mixture of the gases in the cylinder is 27 bar, the partial pressure of N_2 is :[Use atomic masses (in g mol^-1) : N = 14, Ar = 40] Answer: 3. 15 bar Partial pressure p_i=x_i P_total . Moles N₂=7/14=0.25 ; moles Ar =8/40=0.2 . x_(N_2)=0.25/0.45=5/9 . p_(N_2)=5/9×27=15 bar... 1
- The mixture which shows positive deviation from Raoult's law is : Answer: 1. Ethanol + Acetone Positive deviation occurs when A-B attractions are weaker than A-A and B-B. Ethanol has strong hydrogen bonding... 1
- The mixture that forms maximum boiling azeotrope is : Answer: 1. Water + Nitric acid Maximum boiling azeotropes come from solutions with negative deviation from Raoult's law. Nitric acid and wat... 1
- For an ideal solution, the correct option is : Answer: 3. Δ_mixH = 0 at constant T and P For an ideal solution the A-B interactions equal the A-A and B-B interactions. Therefore Δ_mixH =... 1
- If molality of the dilute solution is doubled, the value of molal depression constant (K_f) will be : Answer: 3. unchanged Key idea: K_f is a property of the solvent only. Δ T_f = K_f m . K_f is the depression for a 1 molal solution and depen... 1
- Which of the following is dependent on temperature ? Answer: 1. Molarity Key idea: a concentration term that uses volume changes with temperature, because volume changes. Molarity = moles of so... 1
- The van't Hoff factor (i) for a dilute aqueous solution of the strong electrolyte barium hydroxide is Answer: 3. 3 Key idea: i equals the number of ions per formula unit on complete dissociation. mathrmBa(OH)₂→ Ba²⁺+2OH^- This gives 3 ions, s... 1
- Which one of the following is incorrect for ideal solution? Answer: 3. Δ G_mix=0 Key idea: an ideal solution has no net interaction change on mixing, and mixing is spontaneous. Δ H_mix=0 and Δ U_mix=0... 1
- At 100°C the vapour pressure of a solution of 6.5 g of a solute in 100 g water is 732 mm. If K_b = 0.52, the boiling point of this solution will be : Answer: 1. 101°C Key idea: use the lowering of vapour pressure to get the mole fraction, and then the boiling point elevation. At 100°C pure... 1
- Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct ? Assume that the temperature is constant at 25°C. (Given, Vapour Pressure Data at 25°C, benzene = 12.8 kPa, tol… Answer: 1. The vapour will contain a higher percentage of benzene. Key idea: the component with the higher vapour pressure is more volatile... 1